Vintage Synth Repair

On 8 Apr, 2013, at 10:07 PM, evening1 wrote:

>
>
> I have successfully used the 24" FSR strip from interllink  
> technologies as a replacement in a Pro DGX.
> It;s a few inches longer than needed but there's room to the left of  
> the keyboard for the excess.
> It's been a few years since I did this but I don't recall having to  
> modify the circuit.
>
> It may be possible to cut the sensor to make it fit specific  
> situations but I haven't had the need to use one since.
>
> http://www.digikey.com/product-detail/en/30-61710/1027-1003-ND/2476472
>

On 8 Apr, 2013, at 11:32 PM, Alexis V. Rogers wrote:

>
>
> Tantalums were used due to size and lower ESR. You can get low ESR  
> electrolytics these days. The problem with tantalums is that they  
> close (short) when they fail. When used in a power supply situation,  
> I've seen tantalums burst into flame and end up looking like burnt  
> marshmallows.
>
> I've never added capacitors to the IC power lines unless I was  
> replacing with a different IC whose datasheet called for it.
>
> And, I get my can caps through http://www.tubesandmore.com/.

>
> Thanks for your explanation and the link. So can I take it as a rule  
> of thumb and change all tantalum (in PSU, logic circuits or audio  
> circuits) for low ESR electrolytic? Or is there some case where to  
> change just old tantalum for new one? Could for example using of  
> tantalum rated for higher voltage serve as a sort of better protection  
> against possible fail?
> 
> I had this fire problem with two ceramic disk caps in the PSU of one  
> old Russian instrument which was not in use for few years. Fortunately  
> I could see the fire, it started immediately after switching on, so I  
> just switched off. It was enough to change those caps and instrument  
> is OK, but I will do complete recapping.
> 
> Daniel Forro
> 
> 
> On 8 Apr, 2013, at 11:32 PM, Alexis V. Rogers wrote:
> 
> >
> >
> > Tantalums were used due to size and lower ESR. You can get low ESR  
> > electrolytics these days. The problem with tantalums is that they  
> > close (short) when they fail. When used in a power supply situation,  
> > I've seen tantalums burst into flame and end up looking like burnt  
> > marshmallows.
> >
> > I've never added capacitors to the IC power lines unless I was  
> > replacing with a different IC whose datasheet called for it.
> >
> > And, I get my can caps through http://www.tubesandmore.com/.
>

On 9 Apr, 2013, at 5:00 AM, shupac800 wrote:

> Alexis has it right -- tantalums were used because they pack a lot  
> of capacitance into a very small package.  (Low ESR is good too.)   
> Tantalums are used a lot in cell phones now for the same reason.   
> Now electrolytics in the 1-22 uF range can also be made very small,  
> which was not the case in 1980.
>
> I have seen lots of early 80's units in which the power supply was  
> damaged because of a shorted tantalum cap.  When I work on a  
> synthesizer of this vintage, replacing all tantalums with  
> electrolytics is the first thing I do.  Pay attention to polarity --  
> both tantalums and electrolytics are polarized, so make sure the (+)  
> end of the new electrolytic goes where the (+) leg of the tantalum  
> was.
>
> I wouldn't bother adding capacitors across the power inputs of IC's.
>
> Regarding multiple capacitors -- as far as I know, multiple  
> capacitors (i.e. multiple capacitors in one can) aren't made  
> anymore, so I would wager that any you find are old and no longer  
> "fresh."  Whenever I've had to replace a multiple capacitor, I  
> replace the single multiple cap with individual capacitors of the  
> correct voltages and values.
>
> If space is a problem, get creative -- you can place the new caps  
> somewhere near the original cap location and run wires from their  
> legs to the holes in the PCB where they connect.  (Obviously, the  
> shorter the wires, the better.)  Insulate the solder joints on the  
> cap legs with electrical tape or, better, heat-shrink tubing.  Zip  
> ties or hot glue are useful for holding capacitors in place when  
> they aren't soldered directly to the board.
>
> Remember when replacing electrolytic capacitors that it's always OK  
> to replace them with same value, higher voltage rating.  Also, since  
> most electrolytics are used as ripple/spike filters, their  
> capacitance value is not critical above a certain minimum, meaning  
> that you can replace them with higher value, same voltage rating caps.
>
> --
> David Shuman

From: Daniel Forró

To: vintagesynthrepair@yahoogroups.com

Sent: Monday, April 08, 2013 11:47 PM

Subject: Re: [vintagesynthrepair] Yamaha CS40m problem

Recently I tried to switch on my two CS40m synths which I have used
for the last time about 7 years ago. Main fuse on both machines was
blown after one second.

So I have recapped both PSU, and tried to switch on again. On one
machine big two resistors connected in series to output rails +15 and
-15 V became so hot that their textile envelope (yes, they were
covered by some textile pipe) started to smoke. (On the other machine
not so bad, but again main fuse and another one in the secondary
circuit was blown.) I have immediately switch off, put both PSU out of
the instrument, switched on without a load, and both PSU are OK,
everything works. So I could set all four voltages to their spec
levels (+15, -15, +5, -10).

Am I right to suppose there's a short circuit on some board? I wonder
how it could happen when the instrument was not at all used for years.
In one instrument there was small leakage of RAM battery (as they use
standard 2 AA size batteries in battery compartment, no damage was
caused by this). Otherwise everything looks well.

Has somebody any advice how I should continue and where to find the
source of this problem? Could it be some shorted tantalum capacitor? I
can't use PSU and switch on the instrument. I plan to recap, clean and
check all boards, clean connectors... usual stuff. Then try again to
switch on... If it will work without blowing the fuses or burning
components, then I can check voltages and signals. I have Service
manual.

Thanks in advance for any hint.

Daniel Forro

>
> On the DM board, check the capacitors on the ±15 volt power rails (connector C60. See if they're tantalums and shorted.
> 
> There's two by the connector, but two others elsewhere on the board, so track them down. I'd replace with electrolytics in this case, simple power rails.
> 
> Also, there's a couple on the 5 volt rail too (connector C12), might as well replace those while you're in there.
> 
> Scott in Ohio
> 
> ----- Original Message ----- 
>   From: Daniel Forró 
>   To: vintagesynthrepair@yahoogroups.com 
>   Sent: Monday, April 08, 2013 11:47 PM
>   Subject: Re: [vintagesynthrepair] Yamaha CS40m problem
> 
> 
>     
>   Recently I tried to switch on my two CS40m synths which I have used 
>   for the last time about 7 years ago. Main fuse on both machines was 
>   blown after one second.
> 
>   So I have recapped both PSU, and tried to switch on again. On one 
>   machine big two resistors connected in series to output rails +15 and 
>   -15 V became so hot that their textile envelope (yes, they were 
>   covered by some textile pipe) started to smoke. (On the other machine 
>   not so bad, but again main fuse and another one in the secondary 
>   circuit was blown.) I have immediately switch off, put both PSU out of 
>   the instrument, switched on without a load, and both PSU are OK, 
>   everything works. So I could set all four voltages to their spec 
>   levels (+15, -15, +5, -10).
> 
>   Am I right to suppose there's a short circuit on some board? I wonder 
>   how it could happen when the instrument was not at all used for years. 
>   In one instrument there was small leakage of RAM battery (as they use 
>   standard 2 AA size batteries in battery compartment, no damage was 
>   caused by this). Otherwise everything looks well.
> 
>   Has somebody any advice how I should continue and where to find the 
>   source of this problem? Could it be some shorted tantalum capacitor? I 
>   can't use PSU and switch on the instrument. I plan to recap, clean and 
>   check all boards, clean connectors... usual stuff. Then try again to 
>   switch on... If it will work without blowing the fuses or burning 
>   components, then I can check voltages and signals. I have Service 
>   manual.
> 
>   Thanks in advance for any hint.
> 
>   Daniel Forro
>