Let's Get Technical > All PREAMP Tech Tips & Support
A pair of MP-1 Preamps with issues needing assistance.
kissfan113:
MarshallJMP, I will have to give that a shot, I’ll check the 5v first and try chips next, I don’t have any presets in the second unit and it’s down for my uses until I get replacement jacks for it anyway. (Rear input and headphones) I did pull the cpu chip and the ram chip one on each side of the epromm chip earlier today in the V2 unit with no change in condition or startup process upon restarting the unit. I just ordered some 2032 battery holders and am awaiting their arrival to replace batteries in both units as they both have the original soldered in batteries. I had seen those were the replacement used in the mod, not sure if it’s worth getting the holders for the original battery number or not but if there is a benefit I’ll order them and install the original size battery instead. Still shows an immediate clean indicator and the number 0 button presses don’t change anything, combinations of buttons give another 0 in a different part of the screen and several top leds light but nothing changes in the program. I will update once I get a chance to test the 5v and try the other chips.
Thanks
Kevin
kissfan113:
I will also check that regulator for the proper part number when I get in there.
MarshallJMP:
ADA used different 7805 5V regulators but the 78M05's can fail sometimes at startup (when the current is at it's peak).
It seems it wants to start but can't. Sometimes either U41 or U44 fail, these control the select lines for the RAM and Eprom. Then you can have some strange beheviour too.
Do you have any electronics knowledge? Do you have a oscilloscope?
kissfan113:
I took 3 years into an electronics engineering program, but that was over a decade ago so my skills are pretty rusty, and I’ve forgotten probably as much as I’ve retained. I have a scope but I don’t know that it would do much good it’s an old Simpson model 466 and isn’t in the greatest condition. I could potentially borrow a fluke 196 off my dad long enough to test a few things if it becomes necessary.
kissfan113:
I read 5.0v even across the capacitor next to the z80, 5.0v on pin 14 of U41, 4.4v on pin 14 of U44, the 7805 is labeled (9006, LM340T5, 7805 P) it also resides on a heatsink
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