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Buchla 208r V2.1 (Blue) Build Thread
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page Previous  1, 2, 3 ... , 20, 21, 22  Next [all]
Author Buchla 208r V2.1 (Blue) Build Thread
trimix
I'm working on a few issues... but before I get into those, I wonder if I'm connecting my scope incorrectly...
- I have the probe connected to the output jack leads at the top of the motherboard.
- Output knob all the way CW, Headphones all the way CCW, Preamp level sliders all up, Output channel pots A and B both CW, preamp switches to VCA


The first 5 cards are working really well, Mod oscillator is responding to inputs, but only on AM modulation... and I don't seem to get anything from there on. I do hear a low level output from the mod oscillator, so I'm fairly sure card 5 and 6 are good, but 7/8/9 are (maybe) not outputting. Working on that.

But I want to make sure there isn't a better way to read the output. I would clip the scope to the output pins of the card directly, but because these boards are so interdependent, that wouldn't help
wedaman
wedaman wrote:
Hello everyone.
I need help.

I removed the flux. And I confirmed soldering with a loupe.

I can not hear anything from card 6. Which pin of molex is the MO output of card 6?

And there is sound from card 7. However, moving the FINE TUNING knob and the PITCH slide does not change the sound.
Where is pitch adjustment on card 7?

I used pA726.


I found the schematic. I try to solve it myself.
Thanks. lol
papz
Hi

Are your pA726 good working ? The 3046 should warm up.
The MO is not audible if in low frequency or not properly routed to the LPG2 (signal routing switch in the middle position). Does it modulate the CO when you push the index slider up with the modulation switch set to am of fm ?

The trimmers location is on https://modularsynthesis.com/roman/buchla208v2/208spss.htm
The pA726 calibration instructions on http://www.portabellabz.be/images/pa726/pa726-208.pdf
The schematics on http://www.portabellabz.be/images/208/schemas_208.zip
The 208 calibration instructions and build notes on http://www.portabellabz.be/images/208/208%20build%20notes_final.pdf

Monitoring at the output jacks is ok and what I do but don't do it with all levels all the way up to avoid distortion.
trimix
papz wrote:


Are your pA726 good working ? The 3046 should warm up.
.

Thanks for responding, Papz

I have 4 of the pa726 boards assembled. One is working in Board 6, although I get very little change with the trimmer. I'm not fully satisfied with that, but the 3046 on card 6 is heating up. (seems at one end only however). That's what I thought was a problem at first. I used a TL071 instead of TL061 on all boards

Ive tried the remaining 3 pa726 on card 7, which just stays cold. Trimmer does nothing. I've also swapped the 3046 onto/from the working (?) pa726 and no change, but card 6 still seems to be working the same. I've taken 3046 from the unused boards and swapped them around too. I get different readings at the T* but again the calibration procedure is ineffective so far. So I don't think it's to do with the pa726.
I was very careful to check every joint on Card 7 - no shorts... clean pads; every component is oriented correctly and in the right place. I lifted legs and checked resistors (all 1% or better) and all caps. I swapped the 4136's for new ones, changed the tranny. Molex pin #18 gives me -15v and #17 shows +15v... of course #16 for Q ground and #15 for Noisy ground. The other ones going between boards I have no idea what should be the readings.

The exception to the overall build is the LM301's - no dip8 was available, so I have an SOIC8 on an adapter board in its place throughout the build, including on card 6. That can't be the problem could it? Orientation and contacts have been checked.

So I'm kinda stumped at this point - I've did my due diligence before reaching out for help, but help is welcome. Until the pa726 issue is confidently resolved, I don't feel I should continue the remaining calibrations. It's like card 7 is just dead. I even sprayed cold canned air onto the card to see if there were any warm spots - it just stayed frosty all over!

I'm going to dive into the motherboard tonight, but don't expect to see anything there, because I'm getting voltages on the Molex pins in every position.

I've looked thru all the links you provided, and I'm up with all the changes you suggested , along with those of Dave Brown and Don T.
papz
DIP8 LM301's are easy to find. I got some from this seller which are ok https://www.befr.ebay.be/itm/LM301AN-Amplificateur-operationnel-DIP-8- National-RoHS-Lot-de-5/181746393780?hash=item2a50ede2b4:g:XIsAAOSwFO5a FtRu
I'd replace the SOIC8 ones with these to exclude this as a possible cause.

TL061, TL071, TL081 work on the pA726.
To exclude the pA726 as a cause, you can replace it with a pair of NPN such as 2N3904 (check the µA726 datasheet for pinout) or the SSM2212 adapter for test purpose.
trimix
Will do - thanks. It will take a couple weeks for all the replacements to arrive (also ordered more cd3046) and in the meantime I have another set of PCBs to assemble. I'll see if the second batch have the same problems
Sammus
I got a rare parts kit from boops a little while ago and finally have just opened to use. My kit contains two "7994659 SGS 17026" in place of the MC846P.



I can't anything on the internet at all about that part number - just checking, is it an equivalent part? (and not an error in packing)?

Cheers

Edit: confirmed by boops to be the mil spec version
dingebre
Question re: 218r power. Is the ground on the V2 PCB connected to clean or noisy ground? Or, more likely, am I missing the painfully obvious again...

David
wedaman
Please someone give me some advice.

I have problems with MO.

When the routing switch is centered, the sound of CO can be heard from the output, but the sound of MO is very small at output.

The MO signal reaches the Molex pin 9 of the card 11 from the Molex pin 4 of the card 6 via R 84 (120 K ohm) of the mother board.

I confirmed with the scope that the signal was coming up to R 84. However, the signal becomes weak after R 84 and the waveform is also very small.

Are these correct? What is the function of R84?
papz
Does the MO work as a modulation source ? You can check it with the index section and the mod CV out.
If it works, the problem is likely not in the MO but in the LPG2, on card 11, or in the modulator, on card 5.
You can check the LPG2 with another source : external signal patched to the preamp, with the routing switch in top position, or LPG1 output with the routing switch in bottom position.
wedaman
papz wrote:
Does the MO work as a modulation source ? You can check it with the index section and the mod CV out.
If it works, the problem is likely not in the MO but in the LPG2, on card 11, or in the modulator, on card 5.
You can check the LPG2 with another source : external signal patched to the preamp, with the routing switch in top position, or LPG1 output with the routing switch in bottom position.


Thanks, papz.

I confirmed the mod CV out (pin 11) of card 6 with the scope.
The voltage of pin 11 is DC 4.93 V.
And the voltage of pin 4 is AC 0.668 v.
Card 6 does not seem to work well.

The pA 726 has been calibrated. The soldering has been reconfirmed and the value of the part has been reconfirmed.
Do you have any advice?
papz
I meant the mod CV out banana socket in the top right of the panel.
Can you patch it to a CV input, such as CO pitch or other, and check if it modulates ?

Can you also check if pushing the MO index sliders up modulates the CO pitch (FM) or amplitude (AM) depending on the modulation switch position ?

Also if there's signal on the channel B with the signal routing switch in the lowest position, both LPG1 and LPG2 sliders to 10 and channel A pot to 0 ?
wedaman
papz wrote:
I meant the mod CV out banana socket in the top right of the panel.
Can you patch it to a CV input, such as CO pitch or other, and check if it modulates ?

Can you also check if pushing the MO index sliders up modulates the CO pitch (FM) or amplitude (AM) depending on the modulation switch position ?

Also if there's signal on the channel B with the signal routing switch in the lowest position, both LPG1 and LPG2 sliders to 10 and channel A pot to 0 ?



Thanks for your advice, papz !
I tried it in your way.

I connected a patch from the CV out at the top right of the panel to the CO pitch input.


This is the result.

<balanced external>
I moved MO index sliders up, but it does not change.

<a.m.osc>
I moved the MO index sliders up. The sound of CO gradually became smaller. It is not completely quiet.

<f.m.osc>
I moved the MO index sliders up. The pitch of CO gradually down.


Also, when the routing switch is in the lowest position, both LPG1 and LPG2 sliders to 10.
The sound of channel A becomes smaller, but it does not quiet completely. And channel B became completely quiet.

What is wrong?
Peake
Balanced External is the vactrol "ring modulator" which requires an external signal into the Preamp Aux In jack and the Gate 2 Source switch all the way up and Gate 2's level up as well...
papz
The MO seems working. If you increase the MO frequency, does the CO pitch and amplitude modulation well get faster ?

The issue is probably related to LPG2.
Does the LED light up if you push the LPG2 right slider up ?

You don't seem very familiar with how the 208 works or should work. Do you have the manual ? https://drive.google.com/file/d/0BwtXQvT4dT5hVkpqeDJCMS1fYmM/view?usp= sharing
Sammus
I also have a potential issue with my MO I haven't managed to track down yet.

The MO output looks perfect and seems to modulate as expected, but when I look at it on a scope the CV output and the main output through the LPG looks very different. With MO set to square, the CV out is a nice perfect square wave. Through the LPG (fully open), the voltages decay toward zero, so they're kind of slopey looking squares. At high frequency it looks like a square still, but as the frequency drops the decay becomes very apparent.

I haven't done much troubleshooting at all, and start poking around when I get a chance, but any pointers would be much appreciated.
tarandfeathers
Sammus wrote:
I also have a potential issue with my MO I haven't managed to track down yet.

The MO output looks perfect and seems to modulate as expected, but when I look at it on a scope the CV output and the main output through the LPG looks very different. With MO set to square, the CV out is a nice perfect square wave. Through the LPG (fully open), the voltages decay toward zero, so they're kind of slopey looking squares. At high frequency it looks like a square still, but as the frequency drops the decay becomes very apparent.

I haven't done much troubleshooting at all, and start poking around when I get a chance, but any pointers would be much appreciated.


This is normal behaviour. The audio output amplifiers are capacitively coupled so they will not pass the DC components of the square wave.
Sammus
tarandfeathers wrote:
Sammus wrote:
I also have a potential issue with my MO I haven't managed to track down yet.

The MO output looks perfect and seems to modulate as expected, but when I look at it on a scope the CV output and the main output through the LPG looks very different. With MO set to square, the CV out is a nice perfect square wave. Through the LPG (fully open), the voltages decay toward zero, so they're kind of slopey looking squares. At high frequency it looks like a square still, but as the frequency drops the decay becomes very apparent.

I haven't done much troubleshooting at all, and start poking around when I get a chance, but any pointers would be much appreciated.


This is normal behaviour. The audio output amplifiers are capacitively coupled so they will not pass the DC components of the square wave.


Sweet, I had a slight inkling that may be the case, but not confident enough to make any assumptions. Everything seems fine, in that case smile thanks for putting my mind at ease.
wedaman
papz wrote:
The MO seems working. If you increase the MO frequency, does the CO pitch and amplitude modulation well get faster ?

The issue is probably related to LPG2.
Does the LED light up if you push the LPG2 right slider up ?

You don't seem very familiar with how the 208 works or should work. Do you have the manual ? https://drive.google.com/file/d/0BwtXQvT4dT5hVkpqeDJCMS1fYmM/view?usp= sharing



When I increase the MO frequency, the CO pitch did't amplitude modulation well get faster.

The LED light up when I pushed the LPG2 right slider up.

Thank you for letting me know the link of the manual.

I will check LPG 2 (card 11) again.

I know that it is important that vactrols values match.
What do you think about the resistance value of vactrols? Which is the higher or lower resistance value recommended?
papz
The vactrols matching is not related to this issue.
Vactrols faults are rare and since the panel LED lights up I wouldn't suspect a dead one at first.
Their resistance should be infinite or very high (several Mohms) with the slider to 0 and between around 1K and 1.5K with the slider to 10, measured installed on the board, with the module powered.

Check or replace ICs on board 11 and IC3 on board 5.
4016 and 4136 are usual suspects.
If this doesn't help, check Q1 2N4340 on board 11.

And of course double check the solder joints for a bad one or a bridge, components values and orientation, headers solder joints...
wedaman
papz wrote:
The vactrols matching is not related to this issue.
Vactrols faults are rare and since the panel LED lights up I wouldn't suspect a dead one at first.
Their resistance should be infinite or very high (several Mohms) with the slider to 0 and between around 1K and 1.5K with the slider to 10, measured installed on the board, with the module powered.

Check or replace ICs on board 11 and IC3 on board 5.
4016 and 4136 are usual suspects.
If this doesn't help, check Q1 2N4340 on board 11.

And of course double check the solder joints for a bad one or a bridge, components values and orientation, headers solder joints...



I checked, but vactrols had no problem.

I replaced ICs on board 11 (4066 and 4136), IC 3 (4066) on board 5 and Q 1 2N4340 on board 11.

But there was not any change. Probably this condition will be normal for my 208.
I will calibrate next.

By the way, I am reading the Easel manual in Google Translate. There are many pages!

Papz, thank you for your support.
papz
You're welcome.

If the LPG2 / channel B outputs no signal, I'm afraid this condition is not normal, definitely. wink
wedaman
I'm asking about 5 pots of 208 mother board.
I am using the following pots.

CHANNEL B (A100K)
CHANNEL A (A100K)
REVERB LEVEL (B100K)
MONITOR LEVEL (A100K)
OUTPUT LEVEL (A100K)

However, I noticed it when I saw the DAVE's site. https://modularsynthesis.com/roman/buchla208v2/208%20Motherboard%20fro nt.png
The 50K pots is used.
Please tell me the value of your POT.
Is 100K OK?
papz
Any value from 10k to 100k is ok but a faulty channel B pot could also be a cause.
With a signal routed to LPG2 fully open, you can check for signal with the scope from card 11 pin 3 and trace it untill card 12 pin 11 via the pot and R71 33k resistor on the MB.
wedaman
papz wrote:
Any value from 10k to 100k is ok but a faulty channel B pot could also be a cause.
With a signal routed to LPG2 fully open, you can check for signal with the scope from card 11 pin 3 and trace it untill card 12 pin 11 via the pot and R71 33k resistor on the MB.


I checked, but the above case is no problem.


There seems to be a problem with IC 2 (4066) of card 5.
When I checked by the scope, the signal of MO is coming up to pin 8 of IC 2. However, the waveshapes from pin 9, pin 10, and pin 13 of IC 2 are small and distorted.
I replaced the IC 2, but it was not improved.

Any advice is welcome.
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