Re-capped the power board on my OB-8, now frozen! Help

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WhinyLittleRunt
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Re-capped the power board on my OB-8, now frozen! Help

Post by WhinyLittleRunt » Sun Jan 10, 2016 2:38 am

Boy do I feel stupid...

I have had no issues recapping anything lately, and I decided to do the power supply/power board on the OB-8 to try getting rid of this weird noise issue, and I replaced the filter caps plus any other electrolytics on the board (15uf, 1uf, 6.8uf) - not too many. But anyway, I boot it up, I get no audio and all the lights flash, and if I hit a key everything freezes...

I went back and retouched everything, checked for trace damage etc but everything honestly looks fine... Stupid me should have stopped at the filter caps before just diving in. I dunno... If any of the tech guys can chime in and see if there is something that needs to be done afterward... I also have the factory midi interface installed...
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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by garranimal » Sun Jan 10, 2016 5:11 am

Did you re-calibrate?

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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by WhinyLittleRunt » Sun Jan 10, 2016 5:26 am

No... Actually my test switches don't even work...

Edit: I went ahead and calibrated for +15v and verified the other voltage as stated in the service manual. when I fire it up it freezes in different places each time... Press a key and all 8 voices light simultaneously... No output...
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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by garranimal » Sun Jan 10, 2016 5:56 am

Be sure to check the +15V and -5V and trim those in first. The -15 and +5 should automatically adjust, but verify them anyway.

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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by WhinyLittleRunt » Sun Jan 10, 2016 6:04 am

Sorry I edited my post before - I did do the power supply calibration. Was within spec anyway before I nudged it right to 15 and 5...
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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by synthRodriguez » Sun Jan 10, 2016 3:35 pm

Have you checked the ripple and overall integrity of the DC lines with an oscilloscope?

Maybe you got a bad cap out of the box or lost one leg of a rectifier.

At a minimum, click your DVM to AC and see what you get.

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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by WhinyLittleRunt » Mon Jan 11, 2016 12:35 am

I'm sure the rectifiers are fine, those weren't touched. They had been changed out sometime over the life of the instrument...

That being said, is there anything to be said for "incompatible" rectifiers with higher-rated filter caps? I mean, this is all complete dum-dum speculation...

I don't have a scope. I can check with the DVM but as I mentioned before, at the connectors I and J that link up to the voice boards, I'm getting a solid 15/5v..

What about the chances I damaged the microprocessor somehow? It's on the factory midi interface... I did bend a pin slightly when I took it off but I straightened that out with no problem...

And don't worry - I already regret touching it in the first place...
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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by Reginator » Mon Jan 11, 2016 5:37 am

Hi Runt.
Since you've verified correct voltage try checking that you're getting good ground to the rest of the boards (no high resistance grounds). Check all connectors for proper orientation and seated correctly (maybe one got knocked loose while upgrading the caps).

Microprocessors (chips), transistors and FETs are susceptible to static discharge from your fingers. You should probably get an ESD wrist strap if you don't already have one. Also verify proper orientation of any chip that was removed.

I hope this helps.

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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by synthRodriguez » Thu Jan 14, 2016 1:53 am

WhinyLittleRunt wrote:I can check with the DVM but as I mentioned before, at the connectors I and J that link up to the voice boards, I'm getting a solid 15/5v.
I'm talking about measuring the values with the meter on an AC setting, not DC.

Anything over 15 mV of ripple on the DC lines, when measuring them in AC, is a reason to dig deeper.

Say you have 150 mV of ripple when reading with the meter in AC mode on a line that is reading 15 VDC fine in when reading in DC mode on the meter. You have a problem. You need to read the lines with both meter settings, AC and DC.

DC should be 15/5 VDC;, with an AC setting the value should be close to zero. It's a rudimentary check.

Just trying to help.

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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by madtheory » Thu Jan 14, 2016 3:15 pm

Ya Scottrod is spot on. Ripple would make the microprocessor misbehave.

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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by WhinyLittleRunt » Thu Jan 14, 2016 10:56 pm

Appreciate it, guys.

I'll check this tonight.
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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by WhinyLittleRunt » Fri Jan 15, 2016 12:38 am

madtheory wrote:Ya Scottrod is spot on. Ripple would make the microprocessor misbehave.
Ok, I checked with AC at the pins and it fluctuates from overload to 233v (basically it's just dancing around and doing it in a continuous cycle) - so definitely ripple. Wonder now what I broke...
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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by WhinyLittleRunt » Fri Jan 15, 2016 12:47 am

You know, would it make sense to put the old filter caps back in? My immediate assumption is that I got a bad cap or something....
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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by EdGs » Fri Jan 15, 2016 1:37 am

Definately likely that there is a dodgy cap in the mix. I changed out the styrene s/h caps on my P5 a while back due to corrosion from moisture (Anvil case foam + humidity + years of storage in Florida) and immediately after lost a voice. One of the brand new caps was bad. Thankfully, that's all it was.

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Re: Re-capped the power board on my OB-8, now frozen! Help

Post by WhinyLittleRunt » Fri Jan 15, 2016 2:51 pm

That's scary... I really regret messing with this now because I didn't think it would open a can of worms...

I put the 3 large filter caps back in, left the 470uf in place that I replaced (because I apparently threw the old one out...) and the issue persists, although this time the board isn't frozen, it's doing that thing where a certain set of parameters are lit on patch A1, and then you hit A2 and they change to a different set, and then when you go A3, A4 etc, they just cycle back and forth to the same sequence as the first two... still no audio output. Previously this happened when I disconnected either the bender board or the voice boards from the power board. Still getting weird AC on the DC line.

Oh well - I'm done messing with it. Probably doing more damage than good.
I like vintage synths....

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