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Vintage Synth Repair

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Thread

Plugs for Mini Moog mods

Plugs for Mini Moog mods

2009-07-20 by Scott

There are some rip-off people out there charging TOO MUCH
for older connectors.
These two are used for the Mini

Cinch Jones 302( 2 pin)

Switchcraft S260 ( 3 cond) They have the 2 cond as well

Both are available at www.mouser.com

Go there 1st

Prophet rev 2

2009-09-08 by Terje Winther

Hi all,
I have a Prophet 5 rev 2 in for service. Originally the problem was  
that autotune didn´t work.
Now autotune, program saving and retrieving as well as all voices  
works great.
However, I am unable to get the keyboard to scale correctly. The top 3  
octaves is correct, but the bottom two octaves are slightly off  
scaling, enough to sound out of tune. I am able to trim the DAC  
according to spec, and it helped, but not enough. I tried turning the  
trimmer even further (lower than +5.000), and even though it helped,  
it is not enough, and I reach the end of the trimmer. I checked the  
power and it is slightly off (+15.3V and -14.75V). I could start total  
recalibration of the whole synth, but that is a staggering 80+  
trimmers (which are sealed now), and it seems a bit overkill when all  
I need is adjustment of keyboard scaling.
Any hints appreciated.


Terje Winther
terje.winther@...
http://www.wintherstormer.no/

Re: [vintagesynthrepair] Prophet rev 2

2009-09-09 by Stephen Jones

Sounds like the DAC is not getting some bits. I had the same problem with a P-600, scaling fine at the top but not at the bottom. The fault was that a chip had failed in front of the DAC and the DAC was not getting it's last few bits. There was a pair of 4000 series chips and one had failed partially, I will have to check the schematic later today to see what they were. I have a Rev. 2 to service tomorrow, I will take a look at the schemo today.

Show quoted textHide quoted text
From: Terje Winther
To: vintagesynthrepair@yahoogroups.com
Sent: Wednesday, September 9, 2009 7:24:43 AM
Subject: [vintagesynthrepair] Prophet rev 2

Hi all,
I have a Prophet 5 rev 2 in for service. Originally the problem was
that autotune didn´t work.
Now autotune, program saving and retrieving as well as all voices
works great.
However, I am unable to get the keyboard to scale correctly. The top 3
octaves is correct, but the bottom two octaves are slightly off
scaling, enough to sound out of tune. I am able to trim the DAC
according to spec, and it helped, but not enough. I tried turning the
trimmer even further (lower than +5.000), and even though it helped,
it is not enough, and I reach the end of the trimmer. I checked the
power and it is slightly off (+15.3V and -14.75V). I could start total
recalibration of the whole synth, but that is a staggering 80+
trimmers (which are sealed now), and it seems a bit overkill when all
I need is adjustment of keyboard scaling.
Any hints appreciated.

Terje Winther
terje.winther@ wintherstormer. no
http://www.wintherstormer.no/


Re: [vintagesynthrepair] Prophet rev 2

2009-09-11 by Terje Winther

Hi Stephen,
This was very interesting. If you can find anything there, I would be happy to know. I will look into that myself as well.

Terje




Sounds like the DAC is not getting some bits. I had the same problem with a P-600, scaling fine at the top but not at the bottom. The fault was that a chip had failed in front of the DAC and the DAC was not getting it's last few bits. There was a pair of 4000 series chips and one had failed partially, I will have to check the schematic later today to see what they were. I have a Rev. 2 to service tomorrow, I will take a look at the schemo today.

Show quoted textHide quoted text
From: Terje Winther wintherstormer.no>
To: vintagesynthrepair@yahoogroups.com
Sent: Wednesday, September 9, 2009 7:24:43 AM
Subject: [vintagesynthrepair] Prophet rev 2

Hi all,
I have a Prophet 5 rev 2 in for service. Originally the problem was
that autotune didn´t work.
Now autotune, program saving and retrieving as well as all voices
works great.
However, I am unable to get the keyboard to scale correctly. The top 3
octaves is correct, but the bottom two octaves are slightly off
scaling, enough to sound out of tune. I am able to trim the DAC
according to spec, and it helped, but not enough. I tried turning the
trimmer even further (lower than +5.000), and even though it helped,
it is not enough, and I reach the end of the trimmer. I checked the
power and it is slightly off (+15.3V and -14.75V). I could start total
recalibration of the whole synth, but that is a staggering 80+
trimmers (which are sealed now), and it seems a bit overkill when all
I need is adjustment of keyboard scaling.
Any hints appreciated.

Terje Winther
terje.winther@ wintherstormer. no
http://www.wintherstormer.no/





Re: [vintagesynthrepair] Prophet rev 2

2009-09-12 by Stephen Jones

Hi Terje, check the pair of 4042's at the front of the DAC, U335 and U336 with a scope, sounds like one of these may have failed and the DAC is missing it's least significant bits. If you put your scope on the output pins and play up and down the keyboard there should be some action on the pins. If one of the chips has it's outputs latched up or down then it is probably faulty (you can check that there is data on the chip select lines for these two chips as well before you change either of them).

Steve.

Show quoted textHide quoted text
From: Terje Winther
To: vintagesynthrepair@...m
Sent: Saturday, September 12, 2009 1:31:14 AM
Subject: Re: [vintagesynthrepair] Prophet rev 2

Hi Stephen,

This was very interesting. If you can find anything there, I would be happy to know. I will look into that myself as well.

Terje




Sounds like the DAC is not getting some bits. I had the same problem with a P-600, scaling fine at the top but not at the bottom. The fault was that a chip had failed in front of the DAC and the DAC was not getting it's last few bits. There was a pair of 4000 series chips and one had failed partially, I will have to check the schematic later today to see what they were. I have a Rev. 2 to service tomorrow, I will take a look at the schemo today.

From: Terje Winther
To: vintagesynthrepair@ yahoogroups. com
Sent: Wednesday, September 9, 2009 7:24:43 AM
Subject: [vintagesynthrepair ] Prophet rev 2

Hi all,
I have a Prophet 5 rev 2 in for service. Originally the problem was
that autotune didn´t work.
Now autotune, program saving and retrieving as well as all voices
works great.
However, I am unable to get the keyboard to scale correctly. The top 3
octaves is correct, but the bottom two octaves are slightly off
scaling, enough to sound out of tune. I am able to trim the DAC
according to spec, and it helped, but not enough. I tried turning the
trimmer even further (lower than +5.000), and even though it helped,
it is not enough, and I reach the end of the trimmer. I checked the
power and it is slightly off (+15.3V and -14.75V). I could start total
recalibration of the whole synth, but that is a staggering 80+
trimmers (which are sealed now), and it seems a bit overkill when all
I need is adjustment of keyboard scaling.
Any hints appreciated.

Terje Winther
terje.winther@ wintherstormer. no
http://www.wintherstormer.no/






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