Vintage Synth Repair

Hi folks! 

Does anyone have info on what sort of replacement transformer I should be looking for? I've got one that's blown here, North American model. It's a CSA T63 but I don't have any specs on its ratio or anything. The schematics don't say anything in this regard (or am I missing something?) 

Thanks :)

>>The schematics don't say anything in this regard (or am I missing something?)<<

the schematic I found by googling dates from 1981, & shows that the synth uses +/- 15V & +/- 12V as well as a couple of other lower voltages, all regulated on the power supply board. elsewhere in the synth there is some local 5V regulation.

http://people.su.se/~viklund/service_manuals/flat/

so..

you need to give it something that will do 15-0-15. a centre tapped iron core trafo that can do 15-0-15, or a dual secondary toroidal with two lots of 15V would do. somewhere on the back of the synth should be a power rating, though I would estimate from the schemos that somewhere around 80VA would be adequate.

you might want to change a few components, speculatively, in the power supply first. if the transformer really has been burned up, then there are other problems, most likely electrolytics or failed regulators.

hth-
duncan.

What kind of troubleshooting have you done so far on the PSU? Are you sure no voltage is coming form the transformer? The PSU isn't very complex. A dead short after one of the regulators could damage the regulator (I've had this happen before)Suspect electrolytic capacitors. 

Looks like there are a couple of fuses on the output of the rectifiers too. 

I've also seen bridge rectifiers fail, which I presumed was from a failed cap.

--- In vintagesynthrepair@yahoogroups.com, "duncan" <ferrograph@...> wrote:

>
> >>The schematics don't say anything in this regard (or am I missing something?)<<
> 
> the schematic I found by googling dates from 1981, & shows that the synth uses +/- 15V & +/- 12V as well as a couple of other lower voltages, all regulated on the power supply board. elsewhere in the synth there is some local 5V regulation.
> 
> http://people.su.se/~viklund/service_manuals/flat/
> 
> so..
> 
> you need to give it something that will do 15-0-15. a centre tapped iron core trafo that can do 15-0-15, or a dual secondary toroidal with two lots of 15V would do. somewhere on the back of the synth should be a power rating, though I would estimate from the schemos that somewhere around 80VA would be adequate.
> 
> you might want to change a few components, speculatively, in the power supply first. if the transformer really has been burned up, then there are other problems, most likely electrolytics or failed regulators.
> 
> hth-
> duncan.
>

The psu board could be faulty but I haven't even got that far. Right now just having the transformer connected to the and power switch (with the rest of the synth disconnected) still blows the fuse. The primary checked out. The secondary show something like 3.5 megaohms. That was it. There may very well be more damage further on but as I said, I haven't got that far yet.

Check the rectifiers and cap's downrange for shorts. I had a similar fault on a power rail on an Otari tape deck. Kept blowing fuse, I replaced both the rectifier and the filter capacitor after it, and that solved the problem. 

--- In vintagesynthrepair@yahoogroups.com, "Boddington" <f115@...> wrote:

>
> The psu board could be faulty but I haven't even got that far. Right now just having the transformer connected to the and power switch (with the rest of the synth disconnected) still blows the fuse. The primary checked out. The secondary show something like 3.5 megaohms. That was it. There may very well be more damage further on but as I said, I haven't got that far yet.
>

The secondary of the transformer should show low ohms not high.  A 15V
winding could well have impedance of an ohm or two if not less.  What you
seem to be measuring is an open circuit secondary!  This however should not
blow input fuses.  This suggests that the transformer has shorted turns on
the primary - hence you will need a replacement.  A previous poster
confirmed that there appears from the schematic that you need +-12V and
+-15V, this does not have to be in a single transformer, you could use two
separate units.  A small 50VA transformer for each would almost certainly
suffice.

To connect two transformers you would parallel the input windings and of the
secondary windings common the centre tap and then take the 12V and 15V
windings to the PCB to their appropriate connections together with the
commoned centre taps.

This is not rocket science!

 

Regards

Brian G3OYU

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Boddington
Sent: 31 May 2011 7:22
To: vintagesynthrepair@yahoogroups.com
Subject: [vintagesynthrepair] Re: Crumart Trilogy replacement power
transformer

 

  

The psu board could be faulty but I haven't even got that far. Right now
just having the transformer connected to the and power switch (with the rest
of the synth disconnected) still blows the fuse. The primary checked out.
The secondary show something like 3.5 megaohms. That was it. There may very
well be more damage further on but as I said, I haven't got that far yet.

I check the transformer's primary using a self-made (lopt) inductance tester running at 19KHz. The primary could have shorted turns due to overheating etc., althought usually there is a thermal fuse incorporated inside the transformer as protection that goes o/c. If it blows the main fuse (verify if this is correct) with the secondary disconnected then it is surely bad.

H9000

The psu board could be faulty but I haven't even got that far. Right now just having the transformer connected to the and power switch (with the rest of the synth disconnected) still blows the fuse. The primary checked out. The secondary show something like 3.5 megaohms. That was it. There may very well be more damage further on but as I said, I haven't got that far yet.

This is misleading very few transformers have built in thermal fuses!

 

Regards

Brian G3OYU

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of HAL9000
Sent: 01 June 2011 8:21
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintagesynthrepair] Re: Crumart Trilogy replacement power
transformer

 

  

 

I check the transformer's primary using a self-made (lopt) inductance tester
running at 19KHz. The primary could have shorted turns due to overheating
etc., althought usually there is a thermal fuse incorporated inside the
transformer as protection that goes o/c. If it blows the main fuse (verify
if this is correct) with the secondary disconnected then it is surely bad.

 

H9000

 

  

The psu board could be faulty but I haven't even got that far. Right now
just having the transformer connected to the and power switch (with the rest
of the synth disconnected) still blows the fuse. The primary checked out.
The secondary show something like 3.5 megaohms. That was it. There may very
well be more damage further on but as I said, I haven't got that far yet.

Sorry I disagree, I have met with many with thermal fuses if not to say most of them. One I'm thinking of at the moment was of a high end Technics Arranger (now operating no more) that was still new at the showroom brought to me dead. In some tropical countries they do go o/c because of insufficient ventilation not like other much colder countries.

I'm not into transformers as I give them to my winder for repair but could be thermal fuses in them are for safety reasons stipulated by law.

H9000

This is misleading very few transformers have built in thermal fuses!

Regards

Brian G3OYU

From: vintagesynthrepair@yahoogroups.com [mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of HAL9000
Sent: 01 June 2011 8:21
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintages ynthrepair] Re: Crumart Trilogy replacement power transformer

I check the transformer's primary using a self-made (lopt) inductance tester running at 19KHz. The primary could have shorted turns due to overheating etc., althought usually there is a thermal fuse incorporated inside the transformer as protection that goes o/c. If it blows the main fuse (verify if this is correct) with the secondary disconnected then it is surely bad.

H9000

The psu board could be faulty but I haven't even got that far. Right now just having the transformer connected to the and power switch (with the rest of the synth disconnected) still blows the fuse. The primary checked out. The secondary show something like 3.5 megaohms. That was it. There may very well be more damage further on but as I said, I haven't got that far yet.

See it can be rocket science! :)

I'll check the PSU board once it's up and running again for sure. But to be clear: even IT wasn't connected. Just a cable, switch, fuse, and trafo. The trafo shows the correct ac voltage on the primary and that wacky megaohm measurement on the secondary.

From what I can tell, it needs to be center tapped with a minimum of 36V split down the middle to handle the needs of both sets of voltage outputs. The reason I inquired is because I didn't want to get a replacement that would put too much or too little load on it at 500mA. Wouldn't 50V be overkill? Also - the schematic also hints at 1A after the secondary but the fuse shows a 500mA limit. See whay I'm asking? :D

Have you looked at the schematic?  If not you are fighting in the dark!  You
need to know precisely what voltages are required.  You make the comment
'from what I can tell', this suggests that you haven't looked at the
schematic.  Correct me if I'm wrong but someone posted a link to the
schematic some time ago and pointed out that you need a 15V +- winding and a
12V +- winding.  This does not tally with you guess that it needs a 36V
centre tapped winding!

 

I haven't looked at the schematic and I no longer have the link so I can't
now check.  However if, as you think, you do only need a 36V minimum centre
tapped then I would suggest a 25V - 0 - 25V secondary.  Most circuits used
something like the 78/79 series voltage regulators, if you check the data
sheets for these you will find that they have a maximum voltage in excess of
30V, speaking from memory absolute maximum is 35V.  Now a 25V winding will
give you an absolute maximum voltage of 25 times root 2 which is 35V so this
will be OK.  I've used a 25V centre tapped transformer to produce a 24V DC
supply many times using the 78 series 24V regulators.

 

Your wacky megohm measurement on the secondary does suggest that the
secondary is open circuit.  However I was under the impression that that
under these conditions the fuse blew so unless I've got that wrong how did
you measure the correct mains voltage at the primary?

 

Post me the link to the schematic and I'll try to help you.  Might I suggest
that you email me off list?

 

Regards

Brian G3OYU

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Boddington
Sent: 02 June 2011 12:01
To: vintagesynthrepair@yahoogroups.com
Subject: [vintagesynthrepair] Re: Crumart Trilogy replacement power
transformer

 

  

See it can be rocket science! :)

I'll check the PSU board once it's up and running again for sure. But to be
clear: even IT wasn't connected. Just a cable, switch, fuse, and trafo. The
trafo shows the correct ac voltage on the primary and that wacky megaohm
measurement on the secondary.

From what I can tell, it needs to be center tapped with a minimum of 36V
split down the middle to handle the needs of both sets of voltage outputs.
The reason I inquired is because I didn't want to get a replacement that
would put too much or too little load on it at 500mA. Wouldn't 50V be
overkill? Also - the schematic also hints at 1A after the secondary but the
fuse shows a 500mA limit. See whay I'm asking? :D

My background on transformers is that I used to design them and I can assure
you that at no time did I ever have the need to put a thermal fuse inside of
them.  Fender use thermal fused transformers a lot but it is not the norm.
The main reason why they use them is to reduce the cost by taking them down
to the minimum size they can get away with but this has the unfortunate
result of raising the temperature they operate at!  Properly designed a
transformer has no need for a thermal fuse.

 

I know of no law that requires thermal fuses, but I'm open to those with
better knowledge than me.

 

Regards

Brian G3OYU

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of HAL9000
Sent: 01 June 2011 5:29
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintagesynthrepair] Re: Crumart Trilogy replacement power
transformer

 

  

 

Sorry I disagree, I have met with many with thermal fuses if not to say most
of them. One I'm thinking of at the moment was of a high end Technics
Arranger (now operating no more) that was still new at the showroom brought
to me dead. In some tropical countries they do go o/c because of
insufficient ventilation not like other much colder countries.

I'm not into transformers as I give them to my winder for repair but could
be thermal fuses in them are for safety reasons stipulated by law.

 

H9000

 

  

This is misleading very few transformers have built in thermal fuses!

Regards

Brian G3OYU

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of HAL9000
Sent: 01 June 2011 8:21
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintages ynthrepair] Re: Crumart Trilogy replacement power
transformer

  

I check the transformer's primary using a self-made (lopt) inductance tester
running at 19KHz. The primary could have shorted turns due to overheating
etc., althought usually there is a thermal fuse incorporated inside the
transformer as protection that goes o/c. If it blows the main fuse (verify
if this is correct) with the secondary disconnected then it is surely bad.

H9000

  

The psu board could be faulty but I haven't even got that far. Right now
just having the transformer connected to the and power switch (with the rest
of the synth disconnected) still blows the fuse. The primary checked out.
The secondary show something like 3.5 megaohms. That was it. There may very
well be more damage further on but as I said, I haven't got that far yet.

I agree with you this time although I've met with many transformers that had/have a thermal fuse.

It could be cost or otherwise like you said but cost is also a factor for the manufacturer. There's a difference between what I would like to design and what I find ready made. No need to remind that the thermal fuse is there should the temperature for some reason exceed that for the enamel to melt-down causing s/c ;primary or both depending on the design of the transformer and possibly catching fire. The fuse temp.rating would usually be chosen appropriately so that it opens before insulation meltdown should the transformer heat-up. In some countries the laws concerning safety for electrical equipment are more restricted than others and this could be a requirement by law should someone fit higher fuses both at prim or sec with the equipment going at fault. Cases were reported in countries of houses etc.. that got burned down due to unattended equipement that went at fault.

Thank you for the information as like this we always keep on learning.

Good luck,

H9000

My background on transformers is that I used to design them and I can assure you that at no time did I ever have the need to put a thermal fuse inside of them. Fender use thermal fused transformers a lot but it is not the norm. The main reason why they use them is to reduce the cost by taking them down to the minimum size they can get away with but this has the unfortunate result of raising the temperature they operate at! Properly designed a transformer has no need for a thermal fuse.

I know of no law that requires thermal fuses, but I’m open to those with better knowledge than me.

Regards

Brian G3OYU

I'm basing it entirely on the schematic.

I don't the believe that the windings are 12 & 15 as the message above suggests. Those are only the outputs after the regulators have done their job. You'll also find 9.1V & 6V as part of the rail. See for yourself. Let me know what you think.

http://manuals.fdiskc.com/flat/Crumar%20Trilogy%20Schematic.pdf

It's pretty simple:

According to the schematic you need +21 volts (unregulated) in front of the
15 volts regulator (after rectification and filtering). This should be
sufficient to calculate the required output of the secondary.
Typical input voltage for the 7815/7915 regulators is 23 volts according to
the datasheet with a minimum voltage of 17.7 volts. So the 21 volts figure
is pretty much in the ballpark.

Now, the question is should a 2x15 volts or 2x18 volts transformer be used?
Anything higher than this is too risky (remember the 21 volts required in
front of the regulator!).
A transformer with 15 volts effective output would give something like
21.21 volts maximum output. Minus the voltage drop across the rectifier we
get about 19.81 volts; this is smoothed by the cap.

HOWEVER: The effective voltage is only correct for full load; the voltage
for no load or partial load is higher! One can usually add about 10% here.
So what we end up is 19.81 volts plus 10%: 21.79 volts.

So I'd stick with a 2x15 volts transformer.

OK I've studied the schematic and agree that only a single centre tapped
secondary winding is required.  As per your other reply a 15V - 0 - 15V
secondary will suffice.  The schematic states 21V at the input to the
regulators, allow 1.5V for the volt drop across TWO rectifiers in series so
the required voltage should be 22.5V.  This is almost exactly .  I'm not
sure that the maths figure will reproduce correctly, but in words it is 15
time the square root of 2.

 

The only other thing you need to know is the power rating.  Given that the
input fuse is rated at 500mA and assuming 230V mains (as it is here in the
UK) the maximum power before the fuse should blow is approximately 115VA, so
a transformer rated at 100VA would be ideal.  It is highly likely that an
80VA unit would suffice.  The cost differential between an 80VA and a 100VA
is likely to be minimal so I'd go for 100VA provided there is sufficient
room in the box.

 

Regards

Brian G3OYU

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Boddington
Sent: 02 June 2011 5:44
To: vintagesynthrepair@yahoogroups.com
Subject: [vintagesynthrepair] Re: Crumart Trilogy replacement power
transformer

 

  

I'm basing it entirely on the schematic.

I don't the believe that the windings are 12 & 15 as the message above
suggests. Those are only the outputs after the regulators have done their
job. You'll also find 9.1V & 6V as part of the rail. See for yourself. Let
me know what you think.

http://manuals.fdiskc.com/flat/Crumar%20Trilogy%20Schematic.pdf

> OK I've studied the schematic and agree that only a single centre tapped
> secondary winding is required.  As per your other reply a 15V - 0 - 15V
> secondary will suffice.

I'd go with two separate 15 volts windings! Contrary to most (but not all)
designs I've seen this power supply has separate bridge rectifiers for the
positive and negative rails. The two "inner" connections of the transformer
secondary are NOT connected to each other and are not on GND potential. It
is obvious that only the outputs of the bridge rectifier connect together
to GND.

I think it also has repercussions for the power rating of the transformer
but I would have to look this up in detail.

I suggest that you look at the schematic again - together with the page on
which the various circuit designations are quoted - you will see that the
ends of both secondary windings ARE in fact common and they are definitely
at ground potential.  It is also obvious that the outputs of the bridge
rectifiers and the transformer centre tap are connected together!

 

I stand by my original statement that a centre tapped transformer is
correct.

 

Regards

Brian G3OYU

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Malte Rogacki
Sent: 03 June 2011 9:01
To: vintagesynthrepair@yahoogroups.com
Subject: RE: [vintagesynthrepair] Re: Crumart Trilogy replacement power
transformer

 

  

> OK I've studied the schematic and agree that only a single centre tapped
> secondary winding is required. As per your other reply a 15V - 0 - 15V
> secondary will suffice.

I'd go with two separate 15 volts windings! Contrary to most (but not all)
designs I've seen this power supply has separate bridge rectifiers for the
positive and negative rails. The two "inner" connections of the transformer
secondary are NOT connected to each other and are not on GND potential. It
is obvious that only the outputs of the bridge rectifier connect together
to GND.

I think it also has repercussions for the power rating of the transformer
but I would have to look this up in detail.

At 13:36 Uhr +0100 03.06.2011, Brian wrote:
> I suggest that you look at the schematic again - together with the page on
> which the various circuit designations are quoted - you will see that the
>ends
> of both secondary windings ARE in fact common and they are definitely at
> ground potential.  It is also obvious that the outputs of the bridge
> rectifiers and the transformer centre tap are connected together!

No, they're not. Just look at the PCB. It's the last page of the manual.

What you are saying is of course correct, unfortunately that is not the
whole story is it?  We don't have the PCB or the transformer here so we
cannot assume that there isn't a wire link added to match the cct diagram,
or the possibility that the manufacturer actually used a transformer where
the centre tap is internally connected.

 

Having said all this if the two rails are in fact isolated from the this
could answer why when checking continuity on the secondary a measured value
of several megohms was found, if the test applied the prods to the outer two
ends of the windings.  The measurement would then be via the diodes of the
rectifier.

 

Whatever we are suggesting the PCB does not match the schematic so I would
be very wary of relying on either.  I'd prefer to rely on fundamental
principles.

 

Regards

Brian G3OYU

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Malte Rogacki
Sent: 03 June 2011 3:10
To: vintagesynthrepair@yahoogroups.com
Subject: RE: [vintagesynthrepair] Re: Crumart Trilogy replacement power
transformer

 

  

At 13:36 Uhr +0100 03.06.2011, Brian wrote:
> I suggest that you look at the schematic again - together with the page on
> which the various circuit designations are quoted - you will see that the
>ends
> of both secondary windings ARE in fact common and they are definitely at
> ground potential. It is also obvious that the outputs of the bridge
> rectifiers and the transformer centre tap are connected together!

No, they're not. Just look at the PCB. It's the last page of the manual.

At 17:08 Uhr +0100 03.06.2011, Brian wrote:
> What you are saying is of course correct, unfortunately that is not the whole
> story is it?

I believe it pretty much is the whole story.

> We don't have the PCB or the transformer here so we cannot assume that there
> isn't a wire link added to match the cct diagram, or the possibility that the
> manufacturer actually used a transformer where the centre tap is internally
> connected.

http://www.pmerecords.com/Keyboards/CrumarTrilogy/CrumarTrilogy11.jpg
http://www.pmerecords.com/Keyboards/CrumarTrilogy/CrumarTrilogy14.jpg

Those pictures show the general vicinity of the power supply, including the
transformer and its connector.
I see clearly two red and two yellow wires connecting the transformer to
the power supply PCB which to me indicates two separate secondaries.

> Having said all this if the two rails are in fact isolated from the this
>could > answer why when checking continuity on the secondary a measured
>value of
> several megohms was found, if the test applied the prods to the outer two
>ends > of the windings.  The measurement would then be via the diodes of
>the
> rectifier.

Indeed. It also should make troubleshooting rather simple: The original
poster should simply unplug the transformer from the PCB and then power up.
If it still blows the main fuse: transformer is definitely at fault. If not
he should measure the AC voltage between red-red and yellow-yellow.

> Whatever we are suggesting the PCB does not match the schematic so I would be
> very wary of relying on either.  I'd prefer to rely on fundamental
>principles.

Actually the PCB matches the schematic perfectly (well, nearly perfectly).
I don't see a connection between the three terminals on the schematic,
either. This is just the "dotted outline" going through the terminals, not
a solid connection. Yes, it's not well drawn. Yes, I don't see the ground
connection on the PCB as well but there are various ways to have this one
implemented.

As far as the fundamental principles go: Your scenario would short out one
of the diodes of each rectifier, wouldn't it?

So far all schematics I've seen (admittedly not too many) with separate
bridge rectifiers use a dedicated secondary for each rectifier:

Crumar Performer
Polymoog
Oberheim OB-X
Kawai SX-210/SX-240

and probably many more.

Having been in the service industry as both a service engineer, test
engineer and design engineer since 1956 I can assure you that many circuits
use commoned secondary's for two bridge rectifiers.

 

Also if the as you say the circuit and the PCB only match 'nearly perfectly'
then you cannot possibly rely on either.

 

I think this thread has gone on too long now.  If you wish to continue it
may I suggest we do it off list?

 

Regards

Brian G3OYU

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Malte Rogacki
Sent: 03 June 2011 6:21
To: vintagesynthrepair@yahoogroups.com
Subject: RE: [vintagesynthrepair] Re: Crumart Trilogy replacement power
transformer

 

  

At 17:08 Uhr +0100 03.06.2011, Brian wrote:
> What you are saying is of course correct, unfortunately that is not the
whole
> story is it?

I believe it pretty much is the whole story.

> We don't have the PCB or the transformer here so we cannot assume that
there
> isn't a wire link added to match the cct diagram, or the possibility that
the
> manufacturer actually used a transformer where the centre tap is
internally
> connected.

http://www.pmerecords.com/Keyboards/CrumarTrilogy/CrumarTrilogy11.jpg
http://www.pmerecords.com/Keyboards/CrumarTrilogy/CrumarTrilogy14.jpg

Those pictures show the general vicinity of the power supply, including the
transformer and its connector.
I see clearly two red and two yellow wires connecting the transformer to
the power supply PCB which to me indicates two separate secondaries.

> Having said all this if the two rails are in fact isolated from the this
>could > answer why when checking continuity on the secondary a measured
>value of
> several megohms was found, if the test applied the prods to the outer two
>ends > of the windings. The measurement would then be via the diodes of
>the
> rectifier.

Indeed. It also should make troubleshooting rather simple: The original
poster should simply unplug the transformer from the PCB and then power up.
If it still blows the main fuse: transformer is definitely at fault. If not
he should measure the AC voltage between red-red and yellow-yellow.

> Whatever we are suggesting the PCB does not match the schematic so I would
be
> very wary of relying on either. I'd prefer to rely on fundamental
>principles.

Actually the PCB matches the schematic perfectly (well, nearly perfectly).
I don't see a connection between the three terminals on the schematic,
either. This is just the "dotted outline" going through the terminals, not
a solid connection. Yes, it's not well drawn. Yes, I don't see the ground
connection on the PCB as well but there are various ways to have this one
implemented.

As far as the fundamental principles go: Your scenario would short out one
of the diodes of each rectifier, wouldn't it?

So far all schematics I've seen (admittedly not too many) with separate
bridge rectifiers use a dedicated secondary for each rectifier:

Crumar Performer
Polymoog
Oberheim OB-X
Kawai SX-210/SX-240

and probably many more.

The upper most section of green jumpers on the left of the board are all ground connections, as are pin 11 & 12 on the second rail of jumpers. What I don't yet see is the ground connection from that center tap. The upper most pin above the two yellow and red wires could be meant for that but I don't have anything connected. It looks like it was never used.

Since this discussion went much further than I expected (thank you!) I'll remove this PSU assembly and snap better pics for you. Despite it being a seemingly fundamental and simple topic, I'm intrigued that it wasn't necessarily a quick and wholly straight forward answer.

On a side note, I'm not sure there's room for two transformers. It's super tight there actually.

From everything I've seen so far this is a single transformer with two
separate secondaries. No need for two transformers; a single torroidal one
would do the job and probably fit the space nicely.

Hi again everyone

I finally posted some pics of the Crumar Transformer and PSU. I also acquired another PSU from a Stratus in the mean time and snapped pics of those. There's plenty more if someone would like a specific angle or detail shot.

The working transformer from the Stratus produces 20V AC off the secondary but note that the PSU, while being the same pcb on paper, has less jumper pins on J1 & J2. The Trilogy's transformer must have produced more voltage on the secondary than this Stratus' does.

At 12:46 Uhr +0000 21.06.2011, Boddington wrote:
> The working transformer from the Stratus produces 20V AC off the
>secondary but
> note that the PSU, while being the same pcb on paper, has less jumper pins on
> J1 & J2. The Trilogy's transformer must have produced more voltage on the
> secondary than this Stratus' does.

Why must the Trilogy's transformer have produced more voltage?

Does the 20V figure apply to both secondaries?

How did the transformer of the Trilogy check out on its own? Does it blow
the fuse?

Yes the Trilogy's transformer was blowing the fuse constantly, even without the PSU board attached. Once I tested the Stratus' secondaries and confirmed that it worked I checked out the PSU board to troubleshoot it. I sourced the problem to a dead tantalum cap for for the 7915. It's finally up and running.

The load on the Trilogy appears to be different though. It needs to produce several more outputs on those jumpers. I still don't know what the value is for the T63 but I suspected it would be at least 20 per winding when factoring in the wave rectification's RMS, etc.

Oh yeah - meant to add - each secondary on the T60 is 20V.

Has anyone got a .pdf of the service manual for the Trilogy? I'm about to get mine looked at cause of a problem with filter triggering in the synth section.

Would be very grateful if anyone can oblige!

Neil Boughey

neilnsheila@...
07590 114633

Hi Neil,
Maybe this will help.

http://thesnowfields.com/manuals.html

Regards.
Miraz
www.mirazmusik.com




________________________________

From: Neil Boughey <neil.n.sheila@...>
To: vintagesynthrepair@yahoogroups.com
Sent: Tue, June 21, 2011 12:51:44 PM
Subject: [vintagesynthrepair] Re: Crumart Trilogy replacement power transformer

  
Has anyone got a .pdf of the service manual for the Trilogy? I'm about to get 
mine looked at cause of a problem with filter triggering in the synth section.

Would be very grateful if anyone can oblige!

Neil Boughey

neilnsheila@btinternet.com
07590 114633

Cheers. You are so welcomed and to the snow fields page host. Hope you get your 
trilogy back up.

Best,
Gary Miraz
www.mirazmusik.com
Los Angeles




________________________________

From: Neil Boughey <neil.n.sheila@...>
To: vintagesynthrepair@yahoogroups.com
Sent: Tue, June 21, 2011 1:23:56 PM
Subject: Re: [vintagesynthrepair] Re: Crumart Trilogy replacement power 
transformer

  
Gary, 

Your an absolute gem, just what i needed!

Many, man thanks


Neil Boughey

neilnsheila@...
07590 114633





On 21 Jun 2011, at 21:20, Gary Miraz wrote:

  
>
>
>Hi Neil,
>Maybe this will help.
>
>http://thesnowfields.com/manuals.html
>
>Regards.
>Miraz
>www.mirazmusik.com
>
>
>
>
________________________________
From: Neil Boughey <neil.n.sheila@...>
>To: vintagesynthrepair@yahoogroups.com
>Sent: Tue, June 21, 2011 12:51:44 PM
>Subject: [vintagesynthrepair] Re: Crumart Trilogy replacement power transformer
>
>  
>Has anyone got a .pdf of the service manual for the Trilogy? I'm about to get 
>mine looked at cause of a problem with filter triggering in the synth section.
>
>Would be very grateful if anyone can oblige!
>
>Neil Boughey
>
>neilnsheila@...
>07590 114633
>
>
>
>

Cheers. Thank you

At 19:43 Uhr +0000 21.06.2011, Boddington wrote:

> The load on the Trilogy appears to be different though.

How do you know that?

> It needs to produce several more outputs on those jumpers.

Which doesn't mean a thing unless you know how much additional power those
outputs draw. The load could even be lighter!

> I still don't know what the value is for the T63 but I suspected it would be
> at least 20 per winding when factoring in the wave rectification's RMS, etc.

There are several misunderstandings here.
If you have a circuit with a higehr load you usually go with  transformer
with a higher wattage, not voltage.
Second, the effective voltage will measure significantly higher without any
load. A 15V transformer with a non-connected secondary will measure around
21 volts.
So what you need to measure is the voltage of the secondary while the
circuit is under its typical load.
While you're at it you could also measure the actual load; this will give
us a good idea what wattage the transformer could be.

From my calculations it should be a 2x15V transformer. Using a transformer
with a too high secondary may kill the regulators because the larger
regulation overhead has to be dissipated into heat.

Hi

 

You make a statement that     <A 15V transformer with a non-connected
secondary will measure around 21 volts>             this is not necessarily
true!

 

It will depend solely upon the design of the transformer.  For example
choose a lower Gauss value, increase the amount of iron, increase the wire
gauge for both primary and secondary and you will have very much improved
regulation and the difference between no load and full load may only be a
volt or two.

 

In terms of regulation a laminated core of Is and Es will generally be
better than a toroidal core.  The reason for this is that you can get larger
wire gauges onto laminated types than on a toroid where you have less space
to play with.

 

In a word it is all down to the impedance.  Lower the impedance and improve
the regulation.

 

Regards

Brian G3OYU

I do see what you both mean. The load is another factor and doesn't necessarily mean it requires more voltage. I was reasonably surprised, however, that the T60 was as high as 20 per secondary. I expected less too.