ADA MP-1 Original - No Display

[napynap]

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!

[MarshallJMP]

Problem is that could be a LOT of things.How good are you with electronics?Do you have a meter,a scoope?

[napynap]

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.

[MarshallJMP]

Just to make sure,do you have an MP-1 or an MP-1 classic?

[napynap]

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.

[MarshallJMP]

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.

[napynap]

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...

[rnolan]

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.

[MarshallJMP]

My bad gave you the wrong info ;for the 74LS26 pin7 is ground pin 14 is 5V.

[MarshallJMP]

You can plug in the connector again,else it won't start.

[napynap]

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?

[MarshallJMP]

This was done in ADA factory,they had to use up the old board and changed it the next batch of pcb's.

[napynap]

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...

[MarshallJMP]

Okay 5V seems to be okay,if you power it up does it sequence the leds in the switches?

[napynap]

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.