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A pair of MP-1 Preamps with issues needing assistance.

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kissfan113:
I have a pair of ADA MP-1 preamps that I’m making repairs to. One is a unit that functions well but has the rear input jack and headphone Jack broken and needing replacement. It is a version 1 unit with the top mounted input switch. The second unit is brand new to me, just came in the mail today and I’m having a few problems diagnosing the issues it has. It is a version 2 model without the top input switch. Upon arrival the unit was apparently doa, wouldn’t power up at all. I cycled the switch several times and the unit now comes online and goes directly to the clean indicator lit and the numeral 0 on the display, no self check, no ada or model or program information, no leds on the panel light during startup or with buttons. Preset buttons do nothing, I can however press combinations of buttons like the arrow keys, treble, and one or 2 other buttons and it will illuminate several leds along the strip above the buttons but does nothing to change presets or other parameters. I don’t seem to be getting audio out of the unit either. The battery is stone dead (original soldered in unit) and I plan to replace it with the battery mod during repair just trying to see where I stand before going in depth on other issues. EPROMM chip is version 2.01. Voltage through my Furman pl-plus dmc reads a solid 125 volts. Any help you can provide me in troubleshooting these issues is greatly appreciated.

rnolan:
Hey Kevin, ok your eprom is the last MP-1 version made (v2.01) which added some more factory presets and midi/sysex dump & load basically.  The battery just keeps the RAM powered between power cycles, obviously needs changing but won't be causing the other issues, it should still work when powered on just won't remember any program changes after you turn it off.  So since it's DoA, should you not send it back? or did you know that before you bought it?  One thing you could try which is relatively cheap to do is replace the Z80 CPU, I think I paid $1.50 for one on ebay a while ago, cost more in postage...  Now this won't hurt anything and "should" force a full diagnostic (as will removing the current CPU and re inserting so you can also try that).  MJMP can help you out with the jacks for your working unit (http://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm) and also hopefully help get your new one sorted.

kissfan113:
I knew it was broken going in, took it on as a project based on a description stating it was working but something happened during a previous sale shipping or otherwise so I figured it had to be something somewhat simplistic to repair. The seller did provide me with screenshots of his prior sale complaint and has photos of 3 error codes from the prior buyer, shows err1, err2, err3. He said the prior buyer got those codes then the unit refused to start back up, I just got those photos this morning, after my power cycle I got the condition I posted in my first post.

kissfan113:
Tried a few things today, pulled both tubes and tried to start, no change in condition, tried pulling the cpu, epromm, and memory chips with no change in condition or startup either. The unit almost acts as though the memory has been completely flashed and it holds no original operating data, is that even a possibility?

MarshallJMP:
So you pulled the RAM too? (6264 next to the eprom)

The err1,2,3 codes followed by the counting of C1 to C128 usually mean you had a dead battery. Since you have another mp-1 you could try to swap the eprom and RAM chip. But this will erase the presets from the other MP-1.

Me personally never saw a busted Z80 but that doesn't mean it can't happen. And BTW you can still buy them new.

First thing I would check is that you have a good 5V. On the left side of the Z80 is a small capacitor just next to it. If you measure over it you should be able to measure the 5V. Voltage should be 5V +- 5% (4.75-5.25V)

On the back near the transformer you have 4 voltage regulators, the one on the far right is the 5V regulator for the logic, is it a 78M05?

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