ADA Depot - A Forum To Support Users of ADA Amplification Gear
ADA Preamps => Original MP-1 => Topic started by: napynap on September 30, 2015, 03:11:30 PM
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Hi team!
After many years of collecting dust, I fired up my original ADA MP-1 Classic, but to my horror, the front panel display never lights up. When power cycling the unit, occasionally, I can catch the main LED area (above the MP-1 text) show a program number for a millisecond, but then it goes out. Because of this, nothing happens when I press any of the front buttons. Therefore, I cannot adjust the tone. When plugging a guitar in the front panel jack, I can get the small EQ clip to light up, but that's it. I can hear by guitar through the Left and Right rear output jacks, and the headphone jack. The tubes are nice and amber. I removed the top cover and cleaned it all with air pressure. I discovered it has the original battery soldered to the board (I saw the posts on how to resolve that, which I will). Any ideas why the display won't work, and how I can resolve? Thank you!
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Problem is that could be a LOT of things.How good are you with electronics?Do you have a meter,a scoope?
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Problem is that could be a LOT of things.How good are you with electronics?Do you have a meter,a scoope?
I've taken apart plenty of electronic equipment like VCRs, DVRs, Game systems, Keyboards, Footpedals, etc.. for advanced maintenance or to replace a part.
I'm not afraid to get in and solder stuff, replace components, etc.. (except for dangerous stuff like bias power tubes)
I have an Digital Multimeter by Ideal #61-310, but no scope.
I'm looking at this issue as a project I can learn from, and I'm patient. No rush.
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Just to make sure,do you have an MP-1 or an MP-1 classic?
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Just to make sure,do you have an MP-1 or an MP-1 classic?
It's an original MP-1 with the switch on top, stereo line outputs on rear, does not have the 'classic' writing on the front, just MP-1.
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Ok start by pulling out the grey ribbon cable going from the main board to the midi board.
Then check if you have your +5V,best way to do this is measure it on one of the 74LSxx ic's,pin 1 is 5V,pin 9 is ground.
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Ok start by pulling out the grey ribbon cable going from the main board to the midi board.
Then check if you have your +5V,best way to do this is measure it on one of the 74LSxx ic's,pin 1 is 5V,pin 9 is ground.
Thank you,
OK, I unplugged that big ribbon cable going to where the MIDI ports are (easy). I turned the MP1 ON and measured all the IC 74LSxx on the right side. I put the Red lead(V) on pin 1 (marked by a dot on the ICs), and Black lead(COM) to pin 9, but the chips varied where pin 9 is, and I obtained different voltages for some chips. In the photo, I marked where I thought pin 9 was, and the results below the chip. Awaiting next step...
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As an aside I notice a few resistors and diodes? with lots of flux on the solder joins (compare to others with none), seems to imply some component changes ?
Anyway thought I'd throw it it in case it helped shine some light.
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My bad gave you the wrong info ;for the 74LS26 pin7 is ground pin 14 is 5V.
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You can plug in the connector again,else it won't start.
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As an aside I notice a few resistors and diodes? with lots of flux on the solder joins (compare to others with none), seems to imply some component changes ?
Anyway thought I'd throw it it in case it helped shine some light.
Good eye, I've never made any changes to it, but clearly someone has. I looked at some of the original schematics and general troubleshooting notes that indicate ADA had trouble with some parts in early units and recommended replacing them. Maybe they did it before it was released?
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This was done in ADA factory,they had to use up the old board and changed it the next batch of pcb's.
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My bad gave you the wrong info ;for the 74LS26 pin7 is ground pin 14 is 5V.
OK, back on track, I retested the only 74LS26 chip I found, (second to the right of the battery in my previous photo). Testing the corrected pins is now 5.09v. Awaiting next step...
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Okay 5V seems to be okay,if you power it up does it sequence the leds in the switches?
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Okay 5V seems to be okay,if you power it up does it sequence the leds in the switches?
With the top off, in a completely dark room, I power it up while looking at the front display and the circuit board. The ONLY thing that emits light are the two 12AX7 tubes that begin to glow amber. I never see anything light up at all on the front panel.
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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)
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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)
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Can you post a pic of the tranny and the components right to C131?
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Can you post a pic of the tranny and the components right to C131?
Sure, I think this photo has what you ask for...
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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
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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.
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Since you're mp-1 is a B rev model the cpu schematic is different (look at the NMI input of the cpu).
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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
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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.
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Thanks for the info about those parts, still working on this, but had to delay for holidays/family, etc.. will pick it back up.
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Ok keep us updated. :thumb-up: