Vintage Synth Repair

>>One of the tiny pins on the data bus between the processor and the main memory was lifted due to a bad pick'n'place soldering at the factory.  Looking at the outputs on all of the pins on the bus one-by-one with an oscilloscope, I noticed that the output from the processor was 0-+5V and the input to one of the memory chips for the same trace was +2.5V.  Continuity test with ohmmeter showed broken solder connection.<<

this prompts me to mention that one of the most valuable tools I have in my toolkit is a jeweller's loupe. I had a problem with a yamaha an1x (the analogue modelling synth from 1997) where the bottom octave wouldn't work, but everything else was fine. I too found a pick&place IC (in this instance, the keyboard scanner) with one leg in the air by a fraction of a millimeter. quick dab & everything was ok. the synth had probably been like this since leaving the factory.

duncan.

Great post, much appreciated. 

Of course I vehemently disagree with the statement below. In fact, I think you're joking.

Cheers,

Mu

 
>   Lots of simple things.  Synths, tone modules, and guitar effects are made a lot better now than they were in the 1970s.
>

I picked up a used JV-1010 synth module on eBay that was supposedly 'dead' for US$70 shipped.

Prior to the purchase I asked the seller if he checked the 'wall-wart' supply with a voltmeter - he said he didn't have one and wasn't interested in making the effort himself.

I won the auction and sure enough - bad power supply.

I felt bad for the guy - so I picked up a cheap digital meter ($3) and sent it to him - he now has no excuse not to test his gear.  :-) 

Cheers,
Mike

--- In vintagesynthrepair@yahoogroups.com, "Mu" <anuwup@...> wrote:

>
> Great post, much appreciated. 
> 
> Of course I vehemently disagree with the statement below. In fact, I think you're joking.
> 
> Cheers,
> 
> Mu
> 
>  
> >   Lots of simple things.  Synths, tone modules, and guitar effects are made a lot better now than they were in the 1970s.
> >
>

--- In vintagesynthrepair@yahoogroups.com, "Michael Kirk" <mjkirk12@...> wrote:
>
> I picked up a used JV-1010 synth module on eBay that was supposedly 'dead' for US$70 shipped.
> 
> Prior to the purchase I asked the seller if he checked the 'wall-wart' supply with a voltmeter - he said he didn't have one and wasn't interested in making the effort himself.
> 
> I won the auction and sure enough - bad power supply.
> 
> I felt bad for the guy - so I picked up a cheap digital meter ($3) and sent it to him - he now has no excuse not to test his gear.  :-) 
> 
> Cheers,
> Mike

I bought an ART fx unit off eBay - seller said that the LCD was garbage. It worked fine after a factory reset (!) .. 

I had a Danelectro pedal given to me; its fault was that it needed a new battery .. 

Carlsbro PA amp .. dead .. needed a new HT fuse .. 

Alesis Midiverb .. apparently dead ... wall wart with it was a DC one, unit needed an AC one .. *sigh* ..

Hello,

I don't have any experience with synths made before the mid 1980s. I've studied many guitar stompboxes from the 1970s, however. And I've studied and repaired (to a limited extent) tone modules from the late 1980s on to the early 2000s.

The big difference between the eras is the ICs on the boards. Everything from the mid 80's on is microprocessor-based. Modern stuff is made by pick'n'place robots and 1970s equipment was hand assembled and soldered. The components were a lot bigger and could be repaired easier. The technology for populating and manufacturing the circuit board itself is much more advanced today than it was thirty years ago.

But the boards of today are almost impossible to repair. Even if you knew what the custom chips were and what the programs inside the microprocessors were, you would need expensive special equipment to get the chip off the board without damage to the board, and to put a replacement chip onto the board. Assuming that you could find a replacement chip. So even though the circuit boards are better made today, they are considered disposable and are replaced as a unit instead of tracking down and repairing an individual component.

Guitar stomp boxes are easier to compare. The new ones have cheap phone jacks and really cheap foot switches. Gone are the fat round metal heavy stomp switches of the 70s. Now they would often cost more than the effect. There is a tendency to either stay with 1970s electronic designs (the expensive boutique effects) or to go to digital signal processors. The entire popular Digitech X-series of guitar effects have -exactly- the same circuit board inside the box. There's a big complicated DSP processor, some analog surface-mount signal conditioning components and that's it. All the different effects (phaser, chorus, distortion, delay, etc...) are done by changing the program inside the DSP processor.

>>> I felt bad for the guy - so I picked up a cheap digital meter ($3) and sent it to him - he now has no excuse not to test his gear. :-)<<

I like that story. good karma....


>>The big difference between the eras is the ICs on the boards.  Everything from the mid 80's on is microprocessor-based.  Modern stuff is made by pick'n'place robots and 1970s equipment was hand assembled and soldered.  The components were a lot bigger and could be repaired easier.  The technology for populating and manufacturing the circuit board itself is much more advanced today than it was thirty years ago. 
But the boards of today are almost impossible to repair.<<

I'm inclined to agree, but nevertheless you will sometimes get a rewards for persistence- these expensive multi-layer boards covered in VLSI do occasionally have manufacturing defects like the pick&place bad joints already mentioned. additionally, they can go wrong if airborne contaminants accumulate on the surface & change the electrostatic properties sufficiently (I had a panasonic walkman that would varispeed if the weather was damp- eventually traced this to muck in the servo circuit being electronically activated by humidity). also watch out for simple psu problems (bad bridges, electrolytics, regulators), cracked boards, failed switches, bad joints on sockets, bad opto-isolators on midi gear, this sort of thing can have a non-technical owner writing something off & dumping it for pennies on ebay, while service shops may not have the time or patience to stick with it, & tell the customer it's not worth them even looking for the fault.
besides all this, those of us with engineering in our blood are always up for a challenge, & always looking for the kick that comes from breathing life back into some recalcitrant electronica, especially if it's related to music.

duncan.

Here is my contribution to the movement. I kept a brief database of my repairs in the 80's.  Sorry that it's all uppercase, my knowledge of databases at the time prevented me from using mixed case (I couldn't figure out how to make a search case insensitive).  

Anyway, click on REPAIRS DATABASE:
http://www.MusicTechnologiesGroup.com

GB

Great thread guys.

I've had a few of those -"just needs a fuse or a reset" bargains come  
my way.
Most of the repairs that I've accomplished have been broken traces or  
cold solder joints.
I hit the wall when it comes to testing ICs - any general advice or  
trouble-shooting strategies would be appreciated.
(I guess it depends of what is being tested...)


peace,

jmw

On May 9, 2009, at 6:42 PM, grantpbt wrote:

> Here is my contribution to the movement. I kept a brief database of  
> my repairs in the 80's.  Sorry that it's all uppercase, my knowledge  
> of databases at the time prevented me from using mixed case (I  
> couldn't figure out how to make a search case insensitive).
>
> Anyway, click on REPAIRS DATABASE:
> http://www.MusicTechnologiesGroup.com
>
> GB
>

--- In vintagesynthrepair@yahoogroups.com, John Wieczorek <evening@...> wrote:
>
> Great thread guys.
> 
> I've had a few of those -"just needs a fuse or a reset" bargains come  
> my way.
> Most of the repairs that I've accomplished have been broken traces or  
> cold solder joints.
> I hit the wall when it comes to testing ICs - any general advice or  
> trouble-shooting strategies would be appreciated.
> (I guess it depends of what is being tested...)
> 
> 
> peace,
> 
> jmw
> 

I think you answered your own question .. sometimes I get lucky and look for ICs that are too warm (or cold) for comfort, so I know something is wrong there. Other times, I get a feeling for an output signal not looking right - a chip select decoder that doesn't ever get activated, or maybe a signal doesn't get up to a good voltage .. if the components are socketed, so much the better - substitute known good parts. Oh, and check those power rails to the ICs. I hate to think of the number of times I thought I "knew" that 5v was there, only to find it missing thanks to a nearby track fault. 

I often find with stuff from eBay - especially in the UK - that others have been there before me, trying to repair it. It's fun to try to work out what damage they caused, and what the original fault was. I just sorted out a DX7 keyboard, where one contact spring was bent out of shape. That had caused a note to stick on .. however in trying to fix it (without turning the keyboard over and seeing the bent contact spring) someone had managed to remove the key, and the key next to it, and reassembled them incorrectly so they didn't move .. and then had dropped something onto the power supply board so it had shorted out .. and sometime around then they had put it back together again and put it up for auction ..

>>TOA  	A-912  	10/12/1988  	2322  	7.95  	CALVED<<

is that a technical term? :-)

> >>TOA A-912 10/12/1988 2322 7.95 CALVED<<
>
> is that a technical term? :-)

I don't know.  It might be a typo, but I can't figure out what it should be. 
Otherwise I guess it's just some derisive comment. ;-)

--- In vintagesynthrepair@yahoogroups.com, "GB" <grantbt@...> wrote:
>
> 
> > >>TOA A-912 10/12/1988 2322 7.95 CALVED<<
> >
> > is that a technical term? :-)
> 
> I don't know.  It might be a typo, but I can't figure out what it should be. 
> Otherwise I guess it's just some derisive comment. ;-)
>
TOA makes amplifiers.

Is that it?

> > > >>TOA A-912 10/12/1988 2322 7.95 CALVED<<
> > >
> > > is that a technical term? :-)
> >
> > I don't know. It might be a typo, but I can't figure out what it should 
> > be.
> > Otherwise I guess it's just some derisive comment. ;-)
> >
> TOA makes amplifiers.
>
> Is that it?

I assumed he was referring to "CALVED". Yes TOA make amps, small PA's, etc.

>>I assumed he was referring to "CALVED". Yes TOA make amps, small PA's, etc.<<

correct assumption, shoulda made that clear but these lists don't seem to support italics. 

I was surprised & amused to see "calved" to mean, one presumes, the same as our north-east-england word "raxed" or "smettered", because the entry in the d/b predates bart simpson's "don't have a cow, man!" by some time, implying wider use of bovine references in this area of the US vernacular.

I used to have a toa p.a. amp; it was given to me as a junker & needed a new DC fuse.... 
120W, multiple inputs & outputs (it could drive 4-16 ohm & 70V or 100V line from different taps on the same output trafo), & it could run off mains or 12V battery. wish I still had it.

duncan.

--- In vintagesynthrepair@yahoogroups.com, "duncan" <ferrograph@...> wrote:
>
> >>I assumed he was referring to "CALVED". Yes TOA make amps, small PA's, etc.<<
> 
> correct assumption, shoulda made that clear but these lists don't seem to support italics. 
> 
> I was surprised & amused to see "calved" to mean, one presumes, the same as our north-east-england word "raxed" or "smettered", because the entry in the d/b predates bart simpson's "don't have a cow, man!" by some time, implying wider use of bovine references in this area of the US vernacular.
> 
> I used to have a toa p.a. amp; it was given to me as a junker & needed a new DC fuse.... 
> 120W, multiple inputs & outputs (it could drive 4-16 ohm & 70V or 100V line from different taps on the same output trafo), & it could run off mains or 12V battery. wish I still had it.
> 
> duncan.
>
I have a TOA PA amplifier ..Got it cheap it takes plug-in modules.I have 2 , a phono input and a MIC input.
These are NOT cheap if you buy them new..$1200 or there bouts