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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.
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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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Re: Transcendent 2000 Powertran PCB diagram

Postby midierror » Thu Jan 15, 2015 8:33 pm

Well, I bought it from a church who had it for god knows how long. No-one has messed around with any of it...I`m sure its just the aging process in some way. Having altered RV1 I`ve discovered that it makes no difference to the voltage - really one end to the other does nothing. I`ve used contact cleaner on it too!

Any thoughts?
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Re: Transcendent 2000 Powertran PCB diagram

Postby Folderol » Thu Jan 15, 2015 9:29 pm

Hmm.

First suspect is Q1. With your -probe on IC1 pin 2 what is the voltage on pin 10? This goes across the base-emitter junction of the transistor and should be about 0.6V. Also, what is the voltage from pin 2 to pin 11. This should be around 8 volts, but with your fault is probably a lot lower. If either of these is around 0V it's likely the transistor has failed.

After that it's down to cold (unpowered) checks. You need to ensure there is a path from pin 3 of IC1 round to pin 4, going via R5 and RV1. don't just go across the components as there might be a bad joint or broken track. So, start with everything unpowered and time for all caps to discharge, and go directly across those IC1 pins. With the pot wound round towards R5 you should read about 6k, and with it fully the other way anything from about 8k to 15k (depending on what other hidden resistances there are in the whole unit).
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Re: Transcendent 2000 Powertran PCB diagram

Postby midierror » Thu Jan 15, 2015 10:56 pm

I decided to check my multimeter on some batteries, and it turns out its batteries needed changing. Schoolboy error indeed. So now the power rails are actually running around 17V - but again, the RV3 alterations do nothing...

On IC1 pins 1->10 = 0 and pins 2->11 = 2

IC10
Pin 3: 0V
Pin 6: 6V

IC11
Pin 6: Flying around between 0.01 and 0.2V

I`m flummoxed!? You`ll have shares in this synth by the end of this, thank you so much.

You mentioned not using the 0V for ground as its not connected to the chassis; where should I take it from?
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Re: Transcendent 2000 Powertran PCB diagram

Postby Folderol » Thu Jan 15, 2015 11:32 pm

OK, A couple of mixups here.

What I meant is that you shouldn't use the chassis metalwork for 0V. You should use the actual 0V terminal for most measurements.


You measured between 1 & 10 of IC1 but what I meant was 2 & 10, however the reading you get from 2 & 11 tells me that the transistor is OK, and along with the output voltage of 17V it is being told to give that output.

What is the voltage (to 0V) on pin 4 of IC1 and does it change when you move the pot?



With pin 3 of IC10 being at 0V, either Q9 has gone short circuit (most unlikely) or R39 has gone open circuit or is not getting its -12V supply for some reason (could be a bad joint on the resistor). That would definitely stop the oscillator.

Are you sure pin6 of IC10 is +6V? D12 is a 'clamp' diode and should hold it at no more than +0.6V (when running correctly it should be -0.6V). I wonder, is there any sign of corrosion on this board?
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Re: Transcendent 2000 Powertran PCB diagram

Postby midierror » Fri Jan 16, 2015 1:47 pm

Hello again,

IC1 pin 4 changes between 7-14V when moving the RV...so that indicates it does actually work.

And yes...pin 6 on IC10 does indeed read 0.68V - my apologies. I realise how important these things are, so that won`t happen again! I appreciate your help, I know how much more difficult it is to come to conclusions when the kit is not in front of you.

Are there any components you would advise me buying as replacements?
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