Musitronics Bi-Phase LFO troubles. Voltages posted!!!!

[moogatroid2000]

Hello folks,

I need some assistance if possible.
Here is the numbered run down...

1) I had everything working sans the sine waveform LFO, squarewave was working fine for both LFO and for all intents and purposes it was phasing nicely though a bit choppy do to waveform shape. While trying to suss the issue with the sinewave the square waveform also stopped working. Now it just simply sounds like it is engaged but not pahsing or moving. So in a nutshell I have square waveform only for a short spell and now have neither square nor sine waveform working...
2) Musitronics Bi-Phase, this is an original, not a DIY build.
3) I cannot find the original posting of this schematic and I know it is frowned on to repost but I hope it will be ok in this instance.
http://img293.echo.cx/img293/9890/bp7bg.gif
This is just the schematic for the LFO's. I will be taking voltages for the other areas later tonight if this isn't enough to find the trouble..
4) I have done no mods myself. I did find two ceramic caps soldered between some header pins that looks tacked on. When I couldn't get sine waveform I tried clipping one end of each to see if dumb luck might help. It did not work but I still have square waveforms for at least 10 minutes after I removed the caps, so i kinda doubt they are the cause but maybe someone knows better..Other than this it al looks original to me. I have been inside a few and nothing other than these caps look replaced or out of the oridinary. I had also replaced a 2.2uf cap and a 47uf cap again in the hopes that dumb luck would assist me. Again it did not help but I still had working square waveform after the replacing.
I should mention that my sqaurewave died kinda slowly. I was toggling back and forth and I may have even thought I heard the sine kick in for a second, die, then I switched to square and heard it slowly fade away or out. It was late but I recalled it took a few short seconds and it was gone for good.
5) No part substitutions at all, I did replace two cpas as mentioned above.
6) NA
7) I don't think one applies either as it is powered via transformer, though if there is a similer test I will glady perform it.

OK here are the voltages for this section. I also have some for the input, output and bypass but will wait to post those if needed.

U1:
1- 16.75V-
2- 5.2mv-
3- .744-.780V- fluctuactes
4- 18.42V-
5- 5.1mv-
6- 10.92V-
7- 10.15V+
8- 10.86V+

U2:
1- 5.41V-
2- 5.41V-
3- 5.38V-
4- 18.49V-
5- 17.5mv-
6- 17.5mv-
7- 4.90V+
8- 11.44V-

U3:
1-  38.4mv+
2- 39.5mv+
3- 38.4mv+
4- 18.46V-
5- 17.6mv+
6- 17.2mv+
7- 3.667V-
8- 11.44V+

U5:
1-  16.91V-
2-  0.4mv-
3- .750mv-
4- 18.51V-
5- 3.7mv-
6- 200mv-
7- 10.01V+
8- 10.75V+

U6:
1- 275.1mv-
2- 0.8mv-
3- 0.2mv-
4- 18.53V-
5- 3.7mv-
6- 2.9mv-
7- 269.7mv+
8- 10.75V+


D1:
A- 11.49V+
K- 10.84V+

D2:
A- 1.5mv-
K- 0.7mv+

D3:
A- 16.91V-
K-274 mv-

D4:
A- 16.23V-
K- 16.92V-

D5:
A- 200mv-
K- 275mv-

D6:
A- 200mv-
K- 16.35V-

D7:
A- 30.1mv-
K- 274mv-

D8:
A- 11.49V+
K- 10.76V+


Please let me know if anything looks unusual or if I should start any specific testing of things. Next I aam going to probe voltages on the electrolytics of the LFO section, then onto the phase stage section after a lunchbreak. I will check back her before starting up again in hopes of some guidance.
Thank you all very much.
Jas'

[moogatroid2000]

Here is part 2.

The following is in relation to this schematic covering Input, output and bypass circuits.


U4:
1- 3.2V+
2-  3.1V+
3- 3.1mv+
4- 19.00V-
5- 4.2mv+
6- 4.4mv+
7- 4.1mv+
8 - 11.56V+

U7:
1- 5.2mv+
2- 5.2mv+
3- 3.4mv+
4- 19.10V-
5- 4.2mv+
6- 6.1mv+
7- 6.7mv+
8 - 11.55V+

U8:
1- 2.5mv+
2- 22.6mv+
3- 22.0mv+
4- 19.15V+
5- 4.5mv+
6- 4.3mv+
7- 5.7mv+
8 - 11.55V+

U9:
1- 2.9mv+
2- 20.0mv+
3- 19.7mv+
4- 19.15V-
5- 4.8mv+
6- 6.0mv+
7- 9.0mv+
8 - 11.55V+



I think the polarity of voltage on pin4 of U8 is wrong but will double check them all shortly.

[moogatroid2000]

Part 3.
This is in relation to this schematic and covers the phaser stages.


U1:
1- 22.3mv+
2- 14.7mv+
3- 12.2mv+
4- 18.95V-
5- 12.3mv+
6- 2.9mv+
7- 10.8mv-
8- 11.78V+

U2:
1- 16.2mv+
2- 4.3mv-
3- 11.5mv+
4- 18.95V-
5- 11.4mv+
6- 00.0-00.1mv+
7- 10.6mv-
8- 11.82V+

U3:
1- 11.2mv+
2- 2.8mv+
3- 11.5mv+
4- 18.91V-
5- 11.5mv
6- 4.1mv+
7- 5.4mv+
8- 11.79V+

U4:
1- 2.145V+
2- 37.0mv+
3- 36.3mv+
4- 118.88V-
5- 78.4mv-
6- 75.9mv-
7- 9.65V-
8- 11.75V+

U5:
1- 22.7mv+
2- 17.5mv+
3- 15.3mv+
4- 18.95V-
5- 15.0mv+
6- 8.9mv+
7- 0.06mv-
8- 11.70V+

U6:
1- 21.1mv+
2- 6.4mv+
3- 15.6mv+
4- 19.16V-
5- 15.9mv+
6- 8.6mv+
7- 2.2mv-
8- 11.56V+

U7:
1- 16.1mv+
2- 3.5mv+
3- 15.3mv+
4- 19.14V-
5- 15.4mv+
6- 12.5mv+
7- 7.1mv+
8- 11.55V+

Q1:
E- 1.455V+
B- 2.020V+
C- 11.5V+

Q2:
E- .998V-
B- 9.74V-
C- 11.51V+

D1:
A- 64-67mv+
K- 1.43-1.30V+

D2:
A- 18.2-18.9mv+
K- 2.2mv+

D3:
A- 98.5mv-
K- 2.2mv+

D4:
A- .423mv-
K- .983-.989V-

LED1:
A- 1.001V-
K- .439V-

LED2:
A- 1.1-1.3V+
K- 46-49mv+


Off to double check these voltages and to check the caps. ANyone see somethign amiss? I think I may but I think I will wait until tomorrow before poking around too deeply. Any assistance glady accepted.  

[moogatroid2000]

I am sure I have made some errors in my readings, and will double check them all tomorrow and correct and mistakes I find.

[gez]

Which generator is working, albeit for a short time, No 1 or No2?

All the pin8s have a positive voltage of greater (edit: should have been lesser) magnitude than all the pin4's negative voltage.  Assuming the amps are dual and standard layout, there's a bit of a mismatch there, you'd expect the swing to be even in both directions for a bipolar supply.  Might not mean anything, but something to look at anyway.  I take it this is powered from a wallwart?

Still trying to get my head round some of the schematic, but I take it the 'manual sweep' is a wah type pedal (don't know anything about this effect)?

When the LFO works what happens when you slow it down using the rate pot, does it crap out then?  If you set the rate high and power it up from being off, does it work ok then?

[gez]

PS  Do you have a scope?

[puretube]

THE original:
http://m.bareille.free.fr/biphase/the_vintage.htm
from the page you didn`t find:
http://m.bareille.free.fr/biphase/biphase.htm

[gez]

Thanks for the links Ton.

Looks like one of the caps (C51, the 47u, on schematic 1) might be leaky.

Probably best to replace all the electrolytics seeing as it's an old effect, post your voltages after.

[moogatroid2000]

Groan... I just spent the past hour (here and there inbetween other tasks) replying and sure enough I was asked to log back in and it ate my response.
....Well ok the short version is first a huge thank you for all the help.
I think you mean C5 Gez?
I also think I yanked that cap, did not mark polarity first, convinced myself that all caps negative lead MUST go to ground..... I can't be sure for another couple few hours when I can get to the bench but I think your right and that is where my problem is.
I have a foot to chew on and some egg to remove from my face but I iwll report back asap with findings. If that doesn't do the trick I iwll replay in depth again.
In short both generators were doing ok with square, then they both lost it altogether, as one thing failed and left both gens stranded.
I did note the power voltgae differnces but was unsure what, if anything that meant. I seem to never have truly even bi-polar voltgaes in effetcs, though I suppose the ones I have seen were closer than this one..

Manual sweep is indeed a wah type setup. I think it uses optocouplers but I have doen it with a wah pot and it does sweep. I did not test this function though and was sure the selector was set for LFO sweeping.

I did not test it in that fasion. I did power it many time with the rate nearly all the way up and noticed nothign odd. When trying to use the sinewave on the B generator I could get it to phase by turning it all the way up and then shorting the CCW and wiper. The rate was very fast though and I couldn't make much of it. It would do the same thing if I set the rate to the lowest setting and shorted the CW and wiper. If I tried to turn it, it would give a small amount of play and then the LFO would seem to stop.

I do have a scope, though I have not used it very often, or rather really at all. I always seem to be able to fix things easier than schooling myself with the scope. Though right about now I wish I had learned long ago...

Ok let me post this before I time out again and I will report back asap.

Thanks again to everyone and especially RG for template and procedure to gathering this info, and to Gez who muct have to carry his brain to gigs ina separate case because it is so big!!! Honestly I am in awe that you guys can look at such a thing and see so much more than I. I am learning but at a turtles pace. Anyway thanks everyone again and I'll post back and report asap.
Jas'

[gez]

I think you mean C5 Gez?

C51 in this schematic:

http://m.bareille.free.fr/biphase/vintage/mutron_biphase_sch1.gif

If it's leaky then the current draw through R118 is going to be more than it should be, which would drop some of the supply voltage and might be the cause of the lower V+ reading.

Thanks again to everyone and especially RG for template and procedure to gathering this info, and to Gez who muct have to carry his brain to gigs ina separate case because it is so big!!!

Nah, that's just my head (the brain bit rattles)  

Besides, the thing isn't fixed yet!

[puretube]

:oops:  I would have mentioned electrolytics, too
hadn`t he written in 1st post, that he already swapped them..

and btw: I thought the "automatic log-out"-problem had been solved
in this forum?
(I remember ~2 years ago, there was ~1 minute to reply, and then woopey...)

[moogatroid2000]

Ok I went ahead and replaced all the elctros on all boards save the output caps and also the large 470 uf caps on the supply. I don't have any that large. Before I had only replaced the electros on the main board where I thought the generators were located. I tested each with cap meter and all were good. Also the one I had suspected was in backwards wasn't after all, though I replaced it all the same.
Voltages are still off but a little different. I have about 19V- and 10V+ on pins 4 and 8 of the opamps. I have not gone throught the entire reading again yet. Wanted to report more here and ask if I shoudl use the other schematic to make things easier?

Also I tried to put the rates at full and power the unit on and off and sure enough it will phase for a breif moment and then it's gone again. This works for both square and sinewave. Also if I have one or the other rate at full up and I short out the CCW lug and the wipwer I will get a fast rate phasing that will go away if either the pot is turned slighty or I remove the short. The same will happen if I lower the rate and short the wiper to the CW lug.

Ok I guess I am somewhat stuck again. What should I do next? I guess I will try to test the caps as RG suggests while I wait for a reply.
Also should I use the schematic Ton posted for futher reference?

Thanks again all.

[gez]

I'm off to bed.  Will sleep on it and post tomorrow.  

Time to crack open the scope and dust off the manual?

[gez]

if I have one or the other rate at full up and I short out the CCW lug and the wipwer I will get a fast rate phasing that will go away if either the pot is turned slighty or I remove the short.

So the LFO runs constantly and doesn't crap out with the short?  Try reflowing the joints to the pot and give it a clean.

The same will happen if I lower the rate and short the wiper to the CW lug.

That I'd expect, you're applying more of the square wave's output to the inegrator's input so the rate would increase.

Need to get the scope out and see what's happening at pins 1 and 7 of the amps used for 'generator 1' and 'generator 2'.

[puretube]

or wipe the dust out of the pot...  good night, gez!

mooga...: grab the scope!

[gez]

Whoops, you got in just as I was editing Ton.  Schlaf gut!

[moogatroid2000]

My scope is dusted off, just needs to warm up the tubes. It's a techtronix 615A model with dual trace, and I have two probes with 1X, 10X and ref (I assume for reference?) ready to go. I even have a function generator.
I do not have a maual for the scope but have fooled with it enough that I could put it to use with just a little help setting it properly.
I'll see what I can see on my own and reflow the joints on the pots and clean them up. I'll check back ina few minutes in case anyone is still reading and post what I find.

[moogatroid2000]

Well not too sure what I am looking at yet. I still need to clean and reflow the pots. In retrospect I maybe should have done that first. Anyway I seem to have a more or less sinewave happening at those pins of all opamps on that board. I am unsure which one exactly are just for the gens.  :oops:
Anyway it was fun to fire it up and look at the pretty phospor color.
Off I go to clean pots and reflow joints. Get some rest Gez and thank you for the assitance.

[moogatroid2000]

OK, well I was bored last night so I did some upgrading.
New jrc4558 have replaced all the opamps on the generator, audio in/out, bypass board.
I replaced the large 470 filtering caps on the supply (dug around and found I had two new ones).
I replaced 4 decoupling caps, but there are still at least two near the main power supply board and likely others I have not replaced.
I went ahead and replaced all the diodes on that main board.
All that and nothing has changed.
I put my scope on and I get triangle waveforms on pins 7 of a couple of ICs when first powering up. Then it disappears.
Also I see a square waveform when the switch is set to square but only on one IC.
I am going in to take notes on how my scope is set. Exactly which pins give me what when powering on, etc.
Also reflowed the pots and cleaned them. No change.
I hope you guys haven't given up on me. I know I am in way beyond my skills but I know this problem can be fixed with a little help.
If I am doing anything wrong or have missed and steps of the procedure please let me know.
Back soon,
Jas'

[gez]

Unless I've misunderstood, one of the LFOs works with the rate pot shorted?  In which case the pot is your problem.

Is it PCB mount or wired up?