Author Topic: maestro mps2 ..... where to start?  (Read 1958 times)

iainpunk

Re: maestro mps2 ..... where to start?
« Reply #40 on: June 01, 2022, 10:11:22 AM »
071's might work as well. preforming quite the generic function here.
probably the LM308 would as well, given accommodation for the comp cap is jerry-rigged on. would give the phaser that ''slew rate smoothness'' haha

cheers
« Last Edit: June 01, 2022, 10:12:54 AM by iainpunk »
friendly reminder: all holes are positive and have negative weight, despite not being there.

cheers

Strategy

Re: maestro mps2 ..... where to start?
« Reply #41 on: August 20, 2022, 10:59:31 PM »
Hi all, back with the Oberheim P-100, "almost" the same circuit as Jimi's MPS. I've had progress, following RG's "how to trouble shoot pedals fried by overvoltage" thread, and also thanks to wiring photos from Jimi, I have this gem passing dry signal and phased. BUT, no sweep, have tried all manner of trimmer tweaks and it's like playing the phaser manually, can't find the sweep. I'm bumping up agai st the edge of my troubleshooting experience, can anyone share some suggestions?  Measure voltages on those first two 741's perhaps?
...can a potentiometer get damaged in a "catastrophic" overvoltage event? The owner of this pedal said it was on a pedal board that had a "power surge" in which every pedal died. I had to replace all ICs, electro's, and transistors to get it this far.
Thanks all!
Strategy


Rob Strand

Re: maestro mps2 ..... where to start?
« Reply #42 on: August 20, 2022, 11:54:40 PM »
Quote
BUT, no sweep, have tried all manner of trimmer tweaks and it's like playing the phaser manually, can't find the sweep. I'm bumping up agai st the edge of my troubleshooting experience, can anyone share some suggestions?  Measure voltages on those first two 741's perhaps?

It would be a good idea to make sure the LFO IC5+IC6 is working.
If you set the speed to low you might be able to see IC6 pin 6 going on and off.
Increase the speed and see if it increases.

If that's too hard to see, wire a 10k resistor and a RED LED and connect it from IC6 pin 6 to ground.
The LED should go off and on with the speed.



IC5 pin 2 about 4V
IC5 pin 3 about 4V
IC5 pin 6 will have triangle wave (centered around 4V) you might be able to measure that.

IC6 pin 2 about 4V
IC6 pin 3 will bobble up and down (maybe 3V to 5V, something around 4V anyway)

If the LFO isn't working then there's no way you will get any sweep, regardless of the trimpots.

If your LFO is working progress to the trimpots and perhaps check your JFET orientations.
« Last Edit: August 21, 2022, 12:25:45 AM by Rob Strand »
Send:     . .- .-. - .... / - --- / --. --- .-. -

Strategy

Re: maestro mps2 ..... where to start?
« Reply #43 on: September 13, 2022, 07:19:15 PM »
Ok, a covid reinfection had me off track for a few weeks but I'm back and tested ICs 5 and 6. The LFO is not O'ing, and i get way higher voltages across the IC pins, up around supply voltage:
IC5
1 - 8.35
2 - 8.13
3 - 8.34
4 - 8.36
5 - 8.36
6 - 8.29
7 - 8.29
8-  0

IC6 -
1 - 8.36
2 - 8.35
3 - 8.29
4 - 8.36
5 - 8.36
6 -8.26
7 - 7.96
8 - 0
 There's not a lot upstream of these ICs, so I feel there's a potential to hone in here but I'm puzzled. Advice sincerely appreciated!


Rob Strand

Re: maestro mps2 ..... where to start?
« Reply #44 on: September 13, 2022, 10:36:10 PM »
Those voltages look totally whacked.

Upfront: Are you sure the IC's are inserted correctly?  Are you sure you are reporting the IC pins correctly?
This is the pinout when viewing from the top of the IC (not the solder side of the PCB).


You should be able to use your DMM continuity beeper to confirm pin 4 is connected to ground and pin 7 is going to +7V.  In fact pin 4 of all ICs should connect together and to ground and Pin 7 of all ICs should connect together and go to +7V.

If that's not the case check the IC orientations.    If you want to check further follow some of the IC pins and make sure each pin connects a part that matches the schematic.

It might also help to check the voltages on the other IC's. That might highlight an error, or a problem on a larger scale eg. a wiring error, broken track, bad solder joint.

« Last Edit: September 13, 2022, 10:45:37 PM by Rob Strand »
Send:     . .- .-. - .... / - --- / --. --- .-. -

Strategy

Re: maestro mps2 ..... where to start?
« Reply #45 on: September 13, 2022, 11:38:25 PM »
Thanks Rob!
I counted the IC pins on the correct order.
They are correctly oriented.
I will try the other troubleshooting you recommend.
As I mentioned before as well, effected signal passes and I can modulate phase by turning the trimpot - it sounds really nice. So I believe the issue is confined to the LFO.
So, the 741s I used for IC5 and IC6 are from a different source and batch from the ones in the ohasor section. Could bad ICs turn up a result like i'm seeing? Sadly Im all out of 741s, so I'd need to order more to test
Thanks again for all the help!

Rob Strand

Re: maestro mps2 ..... where to start?
« Reply #46 on: September 13, 2022, 11:46:01 PM »
Thanks Rob!
I counted the IC pins on the correct order.
They are correctly oriented.
I will try the other troubleshooting you recommend.
As I mentioned before as well, effected signal passes and I can modulate phase by turning the trimpot - it sounds really nice. So I believe the issue is confined to the LFO.
So, the 741s I used for IC5 and IC6 are from a different source and batch from the ones in the ohasor section. Could bad ICs turn up a result like i'm seeing? Sadly Im all out of 741s, so I'd need to order more to test
Thanks again for all the help!

The fact pin 4 doesn't have 0V is a sure sign of a large scale problem.    If the ground/0V isn't getting to the ICs then the circuit has no hope of working.   Check the continuity of 0V everywhere, jacks, DC inlet, pots.  Something isn't right there!
Send:     . .- .-. - .... / - --- / --. --- .-. -

pinkjimiphoton

Re: maestro mps2 ..... where to start?
« Reply #47 on: September 22, 2022, 10:38:07 AM »
071's might work as well. preforming quite the generic function here.
probably the LM308 would as well, given accommodation for the comp cap is jerry-rigged on. would give the phaser that ''slew rate smoothness'' haha

cheers

308 would work fine. i don't use tl0xx for anything, i don't care for the sound of jfets personally
  • SUPPORTER
"When the power of love overcomes the love of power the world will know peace."
Slava Ukraini!

pinkjimiphoton

Re: maestro mps2 ..... where to start?
« Reply #48 on: September 22, 2022, 10:39:41 AM »
i know your prob, strat... replace the trimmers. they're hosed.
  • SUPPORTER
"When the power of love overcomes the love of power the world will know peace."
Slava Ukraini!

Strategy

Re: maestro mps2 ..... where to start?
« Reply #49 on: September 22, 2022, 11:56:13 AM »
woah, really? one of 'em gives me phasing when I turn it. did you have to replace the trimmers on yours?