smoking prophet600! fire?!

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smoking prophet600! fire?!

Postby Algorithm » Mon Jun 30, 2014 2:53 pm

I got a prophet 600 here that smoked the place up, looked like it lit a cigarette up after passionate love proving.
The smoke was coming straight from the voltage regulator area. I looked closely after the smoke cleared, I saw that 1 of the ??? 2.2µ (according to schematic) was black, looked like bubbly tar, compared to the others that are blue.
After looking at the board / schematic, there are differences that I do not get. I must have a different rev. of board...
It also appears someone replaced things in the troublesome area before I got it. the solder does not look factory done.

The difference is the regulators have no label, except a number of 1 through 4, the schematic has numbers correlated with where the transformer enters the header, but 1 of those numbers (4) is NC ? & 1 of the regulators has 4... so that cant be right.

also, my board just has c021 printed for every one, where the schematic shows the 2.2µ c301-304...

any ideas?

could anybody take a picture of heatsink/regulator/tinycaps?

thanks
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Re: smoking prophet600! fire?!

Postby Algorithm » Mon Jul 07, 2014 4:09 pm

Figured out the mislabeled board, there is a key in the service manual that cross references the different board rev. labels.

replaced all the 2.2µf tantalums, and all the bad regulators (7805, 7815, 7905).

Powered it on, after a few seconds, heard sizzling, opened it up and saw smoking coming from the heatsink again, but not the same place. It was smoking where the 7815 was this time, left it looking grey.
It also burned up 1 of the 2.2µfs... a different place compared to before again.
the first time the tantalum in the middle of the 4 went, this time it was the 1 closest to the 7805.

Any idea what would cause this?
the 2.2µf I got was 35v. Should these be 50v?
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Re: smoking prophet600! fire?!

Postby Dr. Phibes » Tue Jul 08, 2014 4:37 pm

Sounds suspiciously like the short circuit somewhere on the board that's allowing way too much current to flow. I had a P600 but had little need to open it up so I'm familiar with its internal workings unfortunately. Finding it will be the difficult part
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Re: smoking prophet600! fire?!

Postby Bitexion » Tue Jul 08, 2014 5:53 pm

The wonders of ancient electronics...
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Re: smoking prophet600! fire?!

Postby Algorithm » Tue Jul 08, 2014 6:10 pm

Cool, thank you!

hahaha

Looking at the schematic it shows just a diode bridge and caps between what got smoked up.
I get confused trying to test a bridge made of diodes opposed to a bridge rectifier with 4 legs, theres 8 legs with diodes.

There is 48v coming from the transformer.

If that was making it to the 2.2uf 35v tantalums, that might smoke.

my esr meter turned up 0.1Ω on the 3300uf 16v cap.
that means it is BAD right?

looking for similar nichicon datasheet, it said something like 0.035?
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Re: smoking prophet600! fire?!

Postby Dr. Phibes » Tue Jul 08, 2014 10:06 pm

48v doesn't sound right. On the schematic I'm looking at here one tap should read 36V and the other 15V. I wouldn't be happy seeing 48V where 36V should be and I certainly wouldn't be happy seeing it on the 15V tap.

Just check the rectifiers with a simple diode test.

I wouldn't be too worried about the ESR reading - it increases gradually with time by a small amount. Worse would be a cap that has completely failed and is showing a dead short across its leads
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Re: smoking prophet600! fire?!

Postby Algorithm » Tue Jul 08, 2014 10:44 pm

I should have worded that differently. collectively the taps from the transformer are at around 48v.

the 3300µf cap is 16v...

:oops:

The diode bridge seemed to be working correctly.

I noticed a trace directly connected to that 3300µf cap from where the transformer plug meets the board.
Not sure how the bridge works with that...

Ok, cool. Thanks!
What if it gradually decreased to 0.1 from higher numbers?


Thanks again for the advice. :D

EDIT: I need to go turn this thing on and test the transformer again...
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Re: smoking prophet600! fire?!

Postby Algorithm » Wed Jul 09, 2014 8:09 pm

getting 24v and 48v from the transformer.

I cant read schematics... Looking at the board though?
Looks like a trace goes directly from the transformer to the 16v 3300µf cap.
EDIT: that trace is ground.

Just found out that the ESR meter is probably reading a bunch of other things in circuit...
EDIT: took the caps out, they were all good.

now all I can think of is a cold joint on something replaced, or the bridge.
although the diodes seemed good...

might have to give this board the shotgun approach.
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Re: smoking prophet600! fire?!

Postby Algorithm » Fri Jul 11, 2014 5:05 am

replaced the bridge of diodes, it seemed to fix everything nearly. testing regulators showed that 3 of the 4 were working/outputting +5/-5/-15.
turned it off, turned it back on to do another test on what voltage is going where, then got nothing on the voltage regulators.

I also noticed this thing has a chip in it from 1997.
has 2 boards added on. I have never seen a picture of these mods anywhere else.

EDIT: place your bets
is it the caps?
thermal shutdown?
broken trace?
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Re: smoking prophet600! fire?!

Postby Dr. Phibes » Sat Jul 12, 2014 1:15 am

Mod boards? See if you can whip those out and then check the power supply. I bet theres a short on one of them that burning out everything
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Re: smoking prophet600! fire?!

Postby Algorithm » Sat Jul 12, 2014 4:51 am

Yeah, there is a board with what looks to be an opamp, a few caps... right by the output jack.
there is a board near where the recently marketed firmware update would be also...
Im going to try something else before removing the boards, they look good from both sides.
just interesting I cant find any information about either 1 or pictures.
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Re: smoking prophet600! fire?!

Postby Dr. Phibes » Sat Jul 12, 2014 5:11 am

On the occasion I did open up the P600 I recall it being quite tidy - 3 pcbs and that's about it.

Could you upload a few pictures?
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Re: smoking prophet600! fire?!

Postby Algorithm » Sat Jul 12, 2014 5:44 am

speaking of smoke, maybe there was some holy smoke in this thing...
this came from nippon!

according to fiveG

Ver.6E3.1にアップグレードすることで、プリセット・メモリーが2倍になりMIDIチャンネルの指定ができるようになります。
また、音源にノイズが追加されます。
費用は26,250円です。ご購入と同時なら改造費は10%OFFです。

or

pre-set it by upgrading it with Ver.6E3.1, and memory doubles and comes to be able to appoint the MIDI channel.
In addition, a noise is added to a sound source.
The expense is 26,250 yen. The remodeling costs are 10%OFF if simultaneous with the purchase.

so this thing has a noise generator?! O: (((:

Yeah, I will try to upload some pictures!
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Re: smoking prophet600! fire?!

Postby Algorithm » Wed Jul 16, 2014 11:43 pm

Never got around to taking pictures, but it is definitely the fiveG ver.6E3.1 with noise, etc.

I am surprised that there is not many gaijin mentioning that upgrade...

I am thinking about how I can redesign the PSU section to trim some voltage.

Since the transformer is rated for 100v and not switchable, there is just too much getting sent to the regulators.
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Re: smoking prophet600! fire?!

Postby Algorithm » Fri Aug 08, 2014 10:06 pm

fixed the PSU, now all that is dandy. I used a bucking transformer just to see if the voltage would correspond, and it did. Now this beautiful thing is working, nearly.
The prophet600 has some intermittent keys.
I swapped all voice CEM's around, but still having a random troublesome key/note here or there.
Judging from the looks of it, someone previously tried to replace a few of the cems already. I could tell from the stamp on them, some (the originals) were a dull brown, about 3 or 4 had a completely different font and were white.

This thing sounds amazing when I dodge the dodgy keys. Im not sure how the noise mod circuit works exactly.
Im going to have to translate the instruction manual to know more about it.
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