ADA Depot - A Forum To Support Users of ADA Amplification Gear
Let's Get Technical => All PREAMP Tech Tips & Support => Topic started by: kissfan113 on September 08, 2022, 02:43:24 PM
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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.
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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.
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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.
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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?
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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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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
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I will also check that regulator for the proper part number when I get in there.
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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?
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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.
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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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Replaced all 3 chips (one at a time ram, epromm, z80) with chips from my working mp-1 again no change in startup or function same display, noticed the clip leds dimly light at initial power up sometimes od1 gets brighter but it’s intermittent when it comes on
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Ok, got to thinking a possible dirty connection may be the cause of my issues on the v2 model, I took the ribbon cable connection on and off several times and low and behold the unit fires up in a normal manner, sound output is normal now, all functions work great, I still get error 1,2,3 but I am attributing that to the dead battery and should be solved as soon as the 2032 battery holders come in. That leaves me with battery mods to do on both units and rear input and headphone jacks on the v1 model. MarshallJMP do you know a source for the jacks I need? Thank you to everyone who has helped me along while I’ve been poking at this problem.
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Ok good thinking, strange though, usually if you unplug the connector to the midi board nothing happends, didn't think about this since you had some activity.
7805 is good. Maybe you can find those jacks on Mouser. Are you going to use the rear input? If so this is a line in not a guitar input. It's not the same as with V2 MP-1's.
BTW it's normal that the clip leds go on briefly at startup.
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I’ll check Mouser for the jacks, I know they have a huge catalog so it may take a little while to find what I’m looking for, im planning to leave the V1 as originally built where I have the v2 with the guitar input on both ends just to add some flexibility to my system and have a line input if need arises at some point until then it will probably be in my studio rack where things get plugged into the front input anyway. As best I can tell the jacks I need are 4 pin Jalco jacks.
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Got the batteries replaced today, cleared all errors and working like a new one, all I lack is finding the proper jacks for the V1 unit and all is good in my world.
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Hey Kevin, hey good news re V2 unit :whoohoo!: .
You could do the rear jack mod on the V1 unit, MJMP sells this with all the bits ready to go. It will change the rear jack input to inst instead of line level and while I understand keeping the rear input line level just in case you ever have a need, I struggle to think of a use case (I have thought of 1 or 2 e.g. use the MP-1 as an insert on a mixer channel) that needs it. The mod also changes the front input to a normal jack style (albeit IIRC with slightly longer shank to mount through the front plate) rather than the PCB mounted sockets. (http://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm)
@MJMP, don't you have the headphone jacks in stock again? Your web site says "in stock again".
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rnolan, I think I have located some jacks that match and meet original spec, they’re shipping from denmark so it’ll be a hot minute before I have them in hand, hopefully they work for me. If they fail I’ll likely do the rear input mod and find the proper jack for the headphones, if I can keep both units stock sans battery mod for ease of upkeep I hope to, but that’s a bridge I’ll have to cross when it comes time. I appreciate everyone’s help and I’ll keep updating this post until both units are 100% tip top shape.
Kevin
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Hey Kevin, no worries, :thumb-up:
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Yes I have them in stock, it was the return jack that was out of stock for a while.
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Got the new jacks in the mail and got them installed today, the V1 unit is a working great now, have to track down one case screw and the nut and screw for one side of the transformer and it is 100% good as new. Don’t know how I managed to overlook the missing transformer mounting hardware before but it became very apparent to me today, the case screw I don’t remember losing as I laid all my screws in one spot on the work table but it has certainly disappeared so I’ll have to find a replacement.
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Cool, great news :thumb-up: , yes those little screws can be elusive :dunno: . All my 2nd hand MP-2s are missing a few, but they came like that. You can buy the screws, MJMP posted the specs ages ago, not sure what thread (no pun intended) it was in. You can also get very slightly larger thread for if/when the case screw holes get to loose.
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The screws that holds the lids are 4-40 x 1/4
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Marshall would you happen to know the specs on the transformer screws and nuts for a V1 unit, it has one screw and a nylon nut I wasn’t sure if that was the factory or someone else’s doings
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Do you mean a complete nylon nut or a locknut? Now I never seen either in a MP-1.
For what I can can see these are 6-32 x 1/4 and the nuts have a external tooth washer on them.
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It’s a full nylon nut which I thought was an odd choice for the application, I’ll aim to find the proper hardware
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That's not original for sure.