ADA MP-1 Original - No Display

[MarshallJMP]

Ok it seems it doesn't start up.This can be caused by a lot of things.
Could be the diodes D38,D39
No clock signal (bad crystal,bad C143,149,bad U41)
Bad reset circuit
Voltage too low
No interupt pulses at pin 16 of U29
Check pin26 of U29,should be 5V.If it's low it will keep the Z80 cpu in reset mode.

Also try to start it up without the tubes and see what happends.
Measure the voltage over C131 (3300µF/16V)

[napynap]

Ok it seems it doesn't start up.This can be caused by a lot of things....

Thank you, I numbered your items for easier reference. I don't know with certainty how to check items 1 to 5, but I have answers for items 6 to 8, which I achieved with the unit powered on, and the MIDI board cable connected (the attached photo of what I think is C131 has the MIDI board cable removed for clarity). Maybe these answers will help to narrow the possibilities.

1) Could be the diodes D38,D39
2) No clock signal (bad crystal,bad C143,149,bad U41)
3) Bad reset circuit
4) Voltage too low
5) No interupt pulses at pin 16 of U29
6) Check pin26 of U29,should be 5V.If it's low it will keep the Z80 cpu in reset mode.
   ANSWER=5.07V

7) Also try to start it up without the tubes and see what happends.
   ANSWER= All of the LEDs to the right of the display cycled once extremely quickly and then went out, nothing more.
   ANSWER= I'm noticing now this is randomly happening on several power cycles whether the tubes are in or out.

8) Measure the voltage over C131 (3300µF/16V)
   ANSWER= 11.87V (with Tubes)
   ANSWER= 13.50V (without Tubes)

[MarshallJMP]

Can you post a pic of the tranny and the components right to C131?

[napynap]

Can you post a pic of the tranny and the components right to C131?

Sure, I think this photo has what you ask for...

[MarshallJMP]

Ok that seems to be a B rev,that's an oldie.

Check out these

http://www.marshalljmpmodshop.net/ADA-MP1-startup-problem-check-procedure.pdf
http://www.marshalljmpmodshop.net/ADA-MP1-troubleshooting-tips-1992.pdf

[napynap]

Ok that seems to be a B rev,that's an oldie...

Thank you, now that we seem to know what the real issue is, I'll start researching and troubleshooting everything on start up procedure, and report back here.

[MarshallJMP]

Since you're mp-1 is a B rev model the cpu schematic is different (look at the NMI input of the cpu).

[napynap]

Since you're mp-1 is a B rev model the cpu schematic is different (look at the NMI input of the cpu).

Thank you for the schematic.

Also, I'm getting ready to test the capacitors. Just in case, I decided to first check on availability of replacements. The Mouser parts listed in the Noise Mod are end of life cycle parts, listed as obsolete, non-stocked. I contacted customer service, and they were able to suggest the following replacements, each is about $1.

Nichicon Aluminum Electrolytic Capacitors - Leaded
ADA C129 and C130 - 35volts 2200uF, Mouser part# 647-UVR1V222MHD
ADA C131 - 16volts 3300uF, Mouser part# 647-UVR1C332MHD

[MarshallJMP]

These are not the correct types,you axial leaded not radial leaded.

You can change the 3300 with a 4700

75-30D478M016GK2A

and the 2200

594-2222-138-17222

Now changing these won't solve your problem.

[napynap]

Thanks for the info about those parts, still working on this, but had to delay for holidays/family, etc.. will pick it back up.

[MarshallJMP]

Ok keep us updated.