Let's Get Technical > Troubleshooting Problems
MP-1 no display or LED's
andtimebegins:
I recently got an MP-1 (rev B, 1.38 eprom) which is not working from a friend who pointed me in this direction for help.
The screen flashes on for about a second when I power on. LED's cycle on as well, but completely dissappear after about a second.
Wall voltage: 118v
1. C131 reads 11.9 volts with tubes in, with tubes out 13.2v.
2. Pins 11, 17, 24 and 25 of u29 reads 5.1v with tubes in or out.
3. Pin 16 of u29 reads 3.2v with tubes in or out.
4. Pin 6 of u29 reads 0.65v with tubes in or out
5. Pin 27 and 28 of the u30 reads 5.1v with or without tubes
6. VR4 reads 5.1v
I'm not sure how to test for pulses on pin 16 of u29. Its voltage is consistent with or without tubes.
I swapped out D38 and 39 with new ones.
Swapped out c136 for a new .047 cap.
No changes...
I'm starting to think it could possibly be the crystal? I have a new one on order(hope it's the right one, 12MHz). Should be here in a few days.
I'm wondering if these readings stand out as anything obvious? I don't own an oscilloscope.. but if need be, I could pick one up.
Thank you in advance for any help on this.
andtimebegins:
So, I got the new crystal installed... still no go. Same results as with the old crystal.
hmmm....
andtimebegins:
Figured I'd drop a picture of the power section.
Iperfungus:
Hi!
The unit seems to have the battery mod...
Has it any other mod inside?
It could be a problem related to failing Z80 CPU or EPROM, maybe.
Such failures can originate issues like that (I had a similar experience with another preamp, where the CPU broke and I had to change it: once the job was done, the unit came back 100% healthy).
You definitely need the help of MJMP.
Let's wait for him.
MarshallJMP:
So the leds in the buttons go on from left to right (one by one)?
If so then the display should show 8 from left to right, and then in your case 1.38, this does not happen?
BTW if you could get a scope that would be great -, this way we can troubleshoot it better.
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