Emulator 1 - burned capacitor

[rkfaulhaber]

Just fired up my Emulator 1 this weekend to see how it was doing.  It hasn't been out of storage in probably 5-10 years.  When I turned it on, it seemed to start to boot but then immediately stopped and began to smell bad.  A puff of smoke rose from between the keys.  I unplugged it immediately.

When I opened it up, I found that one capacitor on the output board was fried.  An adjacent capacitor felt slightly soft like it was close to melting, too.  Does anyone know what value capacitors these are?  Is there a service manual available for this..  or, if someone has one, could they take a look and see what values are written on them.
Find a photo here:

http://www.flickr.com/photos/11020728@N07/6186663423/
See the burned capacitor in the center bottom of the photo.
The rear of the instrument is to the left.

Thanks a lot. 
-Richard

[Futureman]

Tantalum capacitor.. It will be the same value as the one next to it.

Aim for one with the same value capacitance (prob 10uF or 1uF) but a higher voltage rating, say 35v instead of 25v etc..

Replace em all if you feel like it.. Def the one next to the charred one..

They are polarized.. So make sure you put em in the right way.. The the + symbol lines up.

[rkfaulhaber]

Hi,
Thank you very much for that tip. 
Before I saw your reply to my message I found this board:
 http://www.oldcrows.net/~oldcrow/synth/tips.txt

Which makes this suggestion regarding tantalum capacitors:
"  For places where tantalum polarized capacitors were used (The Prophet-5
had lots of these), replace them with aluminum electrolytic parts of the
same value.  Tantalum capacitors have a very low WVDC and are the first
parts to die if voltage spikes make it past the power supply defeneses. In
general, replace old aluminum electrolytics with new ones.  Modern
capacitor manufacturing techniques have yielded much better parts, so take
advantage of this. For power supply decoupling on circuit boards, replace
the usually 0.1uF ceramic disc capacitors with monolithic dipped-ceramic
parts.  Do the same for other values of decoupling capacitors in the
circuit."

Do you concur, or should I definitely go with tantalum? 

Thanks for your help!
-Richard

[Futureman]

On my E1, I replaced the few dead (and dying) tantalums with electrolytic caps..

Best of luck.

[Futureman]

Oh ... And note that tantalums only have the positive lead marked with a '+' while electrolytic only have the '-' lead marked.

[rkfaulhaber]

Yesterday, I successfully replaced those two capacitors with electrolyte ones (rated at 35 volts instead of 25 volts).  When I first turned it on, it appeared to be non-functional, with random lights lit up.  The third time I flipped the power switch, the disk drive fired up and it loaded sounds from disk (great!).  When I played it, though, the sound was garbled though I could tell it was definitely playing the sounds as they would ring out and stop with each key press.  I'm not sure if this would have to do with:

1. The capacitors I put in are different from the ones I took out ( the voltage rating is higher).  Are there possibly other parameters of electrolyte caps that I should be mindful of?  When I went looking for them online, I found there is also a tolerance rating.  Do I need to be mindful of this?

or

2. Other components failing as well.

I'm inclined to think it's #2 as within about a minute of the thing being on, another wisp of smoke came out from between the keys.  This time, the cap that's blown (I'm pretty sure it's a cap) is somewhere behind the control panel.  I didn't realize there's a circuit board back there but there is.

Have you had any experience pulling these boards out?  It looks like I need to take out the keyboard first in order to get to them. 

Also, taking your advice to replace all the tantalum caps, I notice there are what appear to be small, blue caps alongside IC packages on the motherboard.  They have codes written on them but apparently no capacitance rating.  Are these caps, or something else?  Should I replace the ceramic caps as well, failing or not? 

Again, thank you Futureman for your advice and help with this. 
I'm curious to know how you use your Emulator 1.  Do you have music available online?  Let me know as I'd like to support a fellow working artist.

-Richard

[EdGs]

The smaller caps alongside the IC's are decoupling caps I believe. Unfortunaately, My E1 is packed away at the moment so I can't physically look at it.

The decoupler caps are usually .1uf though. The only markings on them will be 104 for the value and maybe a code like Z5U. Those are generally pretty reliable.

As for the top board behind the controls, It does take a bit of doing to get it out. the knobs have setscrews the hold them to the shafts of the pots, the slider caps have to be popped off, and then there are 12-14 screws holding the boards in. It has been awhile since I looked at those boards, but I believe there are more tantalum caps on those also (actually, there are 2 circuit boards connected by a short ribbon wire). If you try to remove it, take p[ics and mark your ribbon cables if necessary.

I took all of the boards out of mine beccause I had heavy oxidation/moisture/sticky foam throughout the unit. I haven't been able to work on it in awhile, because we are in the process of moving.

http://www.vintagesynth.com/forum/viewtopic.php?t=58600

Sorry I can't be of more help. Best of luck to you and keep us posted.

[Futureman]

On mine, there was a toasted tant on the control section that went up in smoke.

Tantalum capacitors generally look like a water drop, but upside down.
They also have a tendency to fail over time, and go short circuit. The E1's power supply is so beefy that any tant that fails and goes short circuit promptly gets about 5amps dumped through it, and goes up in smoke.

Replacing the tantalums with electrolytics is fine and would not cause the garbled sound.

I would first replace that burnt one in the control section (as mentioned, it's a bit of a pain to get out.. Dont forget locknuts on the pots)

I'd then reseat every IC in the E1.
Do not remove the IC's
Just pry them up a mm or so, then press em back in.
Obviously do this while power is disconnected.
If no joy after doing that, I'd start thinking about where the fault is occurring.

Generally, from my experience.. If some ram was dud, the sample would be fine, then it may have a bit of garbage, then fine again.

Maybe it's the IC that indexes the ram.

Maybe it's the drive, but seem as it loads the OS it seems unlikely.

D-A conversion? Doubt it as the E1 has 8 individual converters.. So it's not that.

Is the distortion analogue or digital? Maybe the analogue power rails have been pulled out of spec by a dud tantalum capacitor? Measure the voltages on an opamp (after you google where to look) and see if they are correct

These are the things that would cross my mind.