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Transcendent 2000 Powertran PCB diagram

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Transcendent 2000 Powertran PCB diagram

Postby midierror » Fri Jan 09, 2015 8:14 pm

Hello,
So I have one of these babies in immaculate condition - but with (it would seem) a broken oscillator. The envelopes, LFO and Filter can all be tested using the Audio Input and function perfectly.

With all the shoddy scans of the PCB around, I decided to `take one for the team` and redraw all the correct components on one picture. Please feel free to share it!

https://midierror.wordpress.com/2015/01/07/transcendent-powertran-2000-pcb-schematic/

I would appreciate any assistance with getting the oscillator working. Replacing all of the ICs has done nothing.
midierror
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Re: Transcendent 2000 Powertran PCB diagram

Postby Wonks » Fri Jan 09, 2015 8:31 pm

I have one as well, (which has stopped working properly since I obtained it and needs looking at too) but I have the full set of original instructions if that is of any help to you. I don't know what's already out there but I'm happy to get the scanner out and do some decent copies for you.
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Re: Transcendent 2000 Powertran PCB diagram

Postby midierror » Sun Jan 11, 2015 10:01 am

Thanks for the offer, maybe we can assist each other in getting them working? I would love to see scans of the diagram to confirm I havent mis-read anything. I`ll send you my email address now.
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Re: Transcendent 2000 Powertran PCB diagram

Postby Wonks » Sun Jan 11, 2015 12:06 pm

I'll get the scanner out. Most likely suspects would be the electrolytic caps. Probably 35 years old now and liable to have dried out, and if not, to have significantly lower values than they used to.
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Re: Transcendent 2000 Powertran PCB diagram

Postby OneWorld » Sun Jan 11, 2015 1:00 pm

I lament when I read threads like this. I used ot be the proud owner of an ETI4600, built by myself, it became an all consuming passion soldering it all together, great sounding machines but came into being just when anything to do with synths became naff and the guitar took precedence yet again. There again thinking of the nurturing it needed, Oscillators drifting out of tune, no MIDI, maybe am reminiscing. But good luck to you in your search.
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Re: Transcendent 2000 Powertran PCB diagram

Postby Wonks » Sun Jan 11, 2015 3:13 pm

Pdf of the scanned manual pages can be found Here.
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Re: Transcendent 2000 Powertran PCB diagram

Postby Wonks » Sun Jan 11, 2015 3:17 pm

Unfortunately the original manual was just photocopies of the original ETI article, so it didn't start out at the highest resolution to begin with. Very much in the DIY ethos!
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Re: Transcendent 2000 Powertran PCB diagram

Postby Hugh Robjohns » Sun Jan 11, 2015 3:28 pm

midierror wrote:I would appreciate any assistance with getting the oscillator working. Replacing all of the ICs has done nothing.
midierror

The first thing to check is that the power supply is generating the right DC rail voltages because low volts could well stop the oscillator oscillating. High volts could have damaged the opamps, (and the replacements, too). After that, it's a case of checking the voltages around the feedback FET and control transistors. The only electrolytic cap I can see in the Osc circuit is in the ramp/triangle generator. It might have dried out, but that won't stop the oscillator, just alter the shape of the ramp output.

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Re: Transcendent 2000 Powertran PCB diagram

Postby Folderol » Sun Jan 11, 2015 7:56 pm

Interesting - we likes drawings, we does :)

As Hugh said, the PSU voltages have to be the first test. If they are OK my next suggestion would be to set all controls about their mid position then measure the DC voltage on pin 6 of IC11 it should be very a proximately +2.5V.

Another point worth checking, pin 6 of IC 10 should be -0.6V. This provides the bias for Q7, the voltage control transistor.

HTH
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Re: Transcendent 2000 Powertran PCB diagram

Postby midierror » Mon Jan 12, 2015 12:25 pm

Thanks for all of the advice - I`m used to simple synth stuff [pots, sockets, switches etc] so this is a little more advanced, but I`m enthusiastic to learn about it.

*Wonks - thanks for the scans!
*Folderol - thanks for the dual-thread support

Is this something I can check with a multimeter?
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Re: Transcendent 2000 Powertran PCB diagram

Postby Hugh Robjohns » Mon Jan 12, 2015 12:29 pm

midierror wrote:Is this something I can check with a multimeter?

For all the static DC voltages on power rails and bias points, yes, a digital multimeter would be the perfect tool for the job.

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Re: Transcendent 2000 Powertran PCB diagram

Postby midierror » Mon Jan 12, 2015 8:59 pm

I would like to make sure I know exactly where the rails are before I test/my untimely death. Can you point me in the right direction? I realise this makes me sound like an idiot - but I want to be sure of not frying anything!

With the other parts mentioned - multimeter set to DC, black probe on ground (before) red probe on said point?
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Re: Transcendent 2000 Powertran PCB diagram

Postby Folderol » Mon Jan 12, 2015 9:53 pm

Find the powers supply board - it is separate from the rest, and is next to the mains transformer. There are a couple of quite sizeable caps C3 & C4 at the transformer end. On the other edge of the board near C7 and C8 are the three DC rail terminals. +12V, 0V & -12V Bear in mind that 0V is not directly connected to the metal chassis so you shouldn't use that as a convenient connection point!

There is a small adjustment preset on the board, but that should only be used for fine trimming of the v+12V output. If it is significantly wrong, or if the -12V one is, the problem is there.
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Re: Transcendent 2000 Powertran PCB diagram

Postby midierror » Tue Jan 13, 2015 10:24 am

So the power rails are loitering around 15V at these points. Should they be 12V?

The values of the ICs seem to fluctuate alot..

IC10 reads 0.01-0.2
IC11 reads around 0.1



:?
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Re: Transcendent 2000 Powertran PCB diagram

Postby Folderol » Tue Jan 13, 2015 5:12 pm

That's definitely too high - not dangerously, but could upset all sorts of things. Maybe someone has been messing about with RV1 (on the power board). See if you can adjust it down to 12V, as close as possible.

With virtually no voltage on the emitter of Q7 (IC10 output) there will be no charge current for IC11, which could be the problem!

What is the voltage on pin3 of IC10? That is derived from Q9 acting as an 'amplified' diode and should be about -0.6V.
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