Synth-DIY Yahoo! Groups Archives

Dead voice and too fast EG

2014-06-04 by dtonthept@yahoo.com

Hi folks,

I'm wondering if anyone might be able to chip in with regards to the below coupla problems I'm still having on the Polysix I picked up recently (and just successfully switched to the Kiwisix including psu mods). The below's behaviour has been consistent before and after installation of the Kiwisix.

Firstly, voice two isn't sounding. The LED is not lighting, and that's about all I can tell you at this stage. From the threads I've trawled there seems to be a pretty systematic way to troubleshoot this but I haven't been able to locate that information, including what the significance is of the LED not lighting (I've seen threads where a voice isn't sounding but the LED does light....). Can anyone point me in the direction of a step-by-step or otherwise hold my hand for a bit?

Secondly, very strange behaviour from the EG. The AD and R make no change from a value of 0 till roughly 6 (staying as they would at 0) then there's a small change till 8.5 or 9 or so (by which time they sound as you'd imagine they might around 3 or 4) then no change for the remainder of the travel till 10. It's the same with all three of these pots. I tried adjusting VR12 but this just applies an offset to this time for each voice, and doesn't change the fundamental behaviour. I'm totally lost on this one!

Any wisdom, humour, advice, direction, or even solutions most welcome.

Thanks a million,

D :-)

Re: [PolySix] Dead voice and too fast EG

2014-06-04 by Bob Grieb

The voices are enabled by the six gate signals,

which come from IC4 and 5 on the KLM366 board.

The Polysix doesn't check for bad voices or anything

that I am aware of. Check the gate signal for that voice.

If it's not turning on, then maybe change out the 4175 chip.

On the EG testing, I would monitor the voltages at IC10-1,

IC10-7 and IC11-7 in manual mode as you adjust each

front panel control. See if the voltages follow the controls

smoothly, or if they jump to match what you are seeing.

If the behavior is the same for all voices, then it seems it

must be some issue with these voltages, not an EG chip.

If the voltages jump, then I would replace the 4051 (IC18),

assuming the other controls are working OK (DAC is OK).

You may also want to buzz out the connections from IC22 and IC23

to pins 6,9,10, and 11 on IC18. If there is a problem with one of those

signals, it could cause strange behavior on the outputs of that chip.

You should grab a copy of the service manual if you don't already

have it, so that you can check the schematic.

Let us know what you find.

Bob

From: "dtonthept@yahoo.com [PolySix]" <PolySix@yahoogroups.com>
To: PolySix@yahoogroups.com
Sent: Tuesday, June 3, 2014 11:33 PM
Subject: [PolySix] Dead voice and too fast EG

Hi folks,

I'm wondering if anyone might be able to chip in with regards to the below coupla problems I'm still having on the Polysix I picked up recently (and just successfully switched to the Kiwisix including psu mods). The below's behaviour has been consistent before and after installation of the Kiwisix.

Firstly, voice two isn't sounding. The LED is not lighting, and that's about all I can tell you at this stage. From the threads I've trawled there seems to be a pretty systematic way to troubleshoot this but I haven't been able to locate that information, including what the significance is of the LED not lighting (I've seen threads where a voice isn't sounding but the LED does light....). Can anyone point me in the direction of a step-by-step or otherwise hold my hand for a bit?

Secondly, very strange behaviour from the EG. The AD and R make no change from a value of 0 till roughly 6 (staying as they would at 0) then there's a small change till 8.5 or 9 or so (by which time they sound as you'd imagine they might around 3 or 4) then no change for the remainder of the travel till 10. It's the same with all three of these pots. I tried adjusting VR12 but this just applies an offset to this time for each voice, and doesn't change the fundamental behaviour. I'm totally lost on this one!

Any wisdom, humour, advice, direction, or even solutions most welcome.

Thanks a million,

D :-)

Re: Dead voice and too fast EG

2014-06-05 by dtonthept@yahoo.com

Hi Bob,

Thanks so much for the reply, hugely appreciated. I've got a friend popping by soon who is much cleverer than I, I'll let you know what we discover. Great to have some clear direction from you on what to check out.

More soon,

D :-)

Re: Dead voice and too fast EG

2014-06-06 by dtonthept@yahoo.com

Hi Bob,

Okay so we've had a bit of a poke around... Thanks a million for the pointers, VERY useful.

The dead voice does indeed stem from a lack of voltage from the appropriate pin on a 4175 so we'll need to replace that. I had a look on Syntaur and they don't have 4175s, indeed an ebay search turned up nothing as well, however they do have a 4174 flip flop - are these interchangeable?

IC, MC14174B Flip-Flop

IC, MC14174B flip-flop.

View on www.syntaur.com

Preview by Yahoo

Otherwise would you have any suggestions for a replacement?

Secondly, we were trying to get voltages for IC10 and IC11. These voltages didn't change when I adjusted the controls, but they did move as the envelope cycled.

What's interesting is that when we were probing pin1 of IC11, suddenly the envelopes (which were set to maximum ADR) began playing exactly as you'd expect! It was a sudden miracle, which, unfortunately, only lasted for maybe 20 or so seconds before the behaviour reverted back to its normal problematic self.

We spent a bit of time prodding the board to see if we could recreate the normal behaviour but didn't have any luck.

We ran out of time just as we were trying to figure out the last bit of your instructions, by "buzz out" do you mean monitor the voltage the whole way along the signal path between those points?

Let me know if the sudden "correct" behaviour triggers any other suggestions, and otherwise please accept my sincere thanks for your help so far.

Best wishes,

D :-)

Re: [PolySix] Re: Dead voice and too fast EG

2014-06-06 by eidorian@aladan.net

On 2014-06-05 20:00, dtonthept@yahoo.com [PolySix] wrote:

> The dead voice does indeed stem from a lack of voltage from the
> appropriate pin on a 4175 so we'll need to replace that. I had a look
> on Syntaur and they don't have 4175s, indeed an ebay search turned up
> nothing as well, however they do have a 4174 flip flop - are these
> interchangeable?

Definitely not - different pinout, different number of flip-flops.
It's a 14175 you want - it's a bit hard to see on the schematics. This
is a reasonably run-of-the-mill IC, not a synth special. Try a bigger
company like Farnell?

http://au.element14.com/on-semiconductor/mc14175bcpg/flip-flop-type-d/dp/1607714

Cheers,
A.

Re: [PolySix] Re: Dead voice and too fast EG

2014-06-06 by Bob Grieb

74C175 should also be OK.

Maybe try flexing the board near where you were probing to

see if that's what made it work. Maybe you have a flaky connection

somewhere?

Buzzing out means using an ohmmeter to check continuity between

the different chips that should connect together. You can't monitor

the digital signals without an oscilloscope.

Bob

From: "dtonthept@yahoo.com [PolySix]" <PolySix@yahoogroups.com>
To: PolySix@yahoogroups.com
Sent: Thursday, June 5, 2014 11:00 PM
Subject: [PolySix] Re: Dead voice and too fast EG

Hi Bob,

Okay so we've had a bit of a poke around... Thanks a million for the pointers, VERY useful.

The dead voice does indeed stem from a lack of voltage from the appropriate pin on a 4175 so we'll need to replace that. I had a look on Syntaur and they don't have 4175s, indeed an ebay search turned up nothing as well, however they do have a 4174 flip flop - are these interchangeable?

IC, MC14174B Flip-Flop

IC, MC14174B flip-flop.

View on www.syntaur.com

Preview by Yahoo

Otherwise would you have any suggestions for a replacement?

Secondly, we were trying to get voltages for IC10 and IC11. These voltages didn't change when I adjusted the controls, but they did move as the envelope cycled.

What's interesting is that when we were probing pin1 of IC11, suddenly the envelopes (which were set to maximum ADR) began playing exactly as you'd expect! It was a sudden miracle, which, unfortunately, only lasted for maybe 20 or so seconds before the behaviour reverted back to its normal problematic self.

We spent a bit of time prodding the board to see if we could recreate the normal behaviour but didn't have any luck.

We ran out of time just as we were trying to figure out the last bit of your instructions, by "buzz out" do you mean monitor the voltage the whole way along the signal path between those points?

Let me know if the sudden "correct" behaviour triggers any other suggestions, and otherwise please accept my sincere thanks for your help so far.

Best wishes,

D :-)

Re: Dead voice and too fast EG

2014-06-07 by dtonthept@yahoo.com

Okay cool thanks guys, I've got the replacement chip you recommended on the way, plus a decent oscilloscope to try to nail that EG gremlin.

Might be a few days before I report back, thanks a million till then!

D :-)

Re: [PolySix] Re: Dead voice and too fast EG

2014-06-07 by Bob Grieb

Hi,

I uploaded some scope photos for comparison when you get things

set up to look at your waveforms.

Let me know if there are other signals I should capture.

Bob

From: "dtonthept@yahoo.com [PolySix]" <PolySix@yahoogroups.com>
To: PolySix@yahoogroups.com
Sent: Thursday, June 5, 2014 11:00 PM
Subject: [PolySix] Re: Dead voice and too fast EG

Hi Bob,

Okay so we've had a bit of a poke around... Thanks a million for the pointers, VERY useful.

The dead voice does indeed stem from a lack of voltage from the appropriate pin on a 4175 so we'll need to replace that. I had a look on Syntaur and they don't have 4175s, indeed an ebay search turned up nothing as well, however they do have a 4174 flip flop - are these interchangeable?

IC, MC14174B Flip-Flop

IC, MC14174B flip-flop.

View on www.syntaur.com

Preview by Yahoo

Otherwise would you have any suggestions for a replacement?

Secondly, we were trying to get voltages for IC10 and IC11. These voltages didn't change when I adjusted the controls, but they did move as the envelope cycled.

What's interesting is that when we were probing pin1 of IC11, suddenly the envelopes (which were set to maximum ADR) began playing exactly as you'd expect! It was a sudden miracle, which, unfortunately, only lasted for maybe 20 or so seconds before the behaviour reverted back to its normal problematic self.

We spent a bit of time prodding the board to see if we could recreate the normal behaviour but didn't have any luck.

We ran out of time just as we were trying to figure out the last bit of your instructions, by "buzz out" do you mean monitor the voltage the whole way along the signal path between those points?

Let me know if the sudden "correct" behaviour triggers any other suggestions, and otherwise please accept my sincere thanks for your help so far.

Best wishes,

D :-)