ADA MP-1 Extreme Restoration

[SteveFuzz]

Hello.

I've just bought an ADA MP-1 in a flea market.
For 10 Euro I decided to give it a try.

The unit is in real bad shape but I'm gonna restore it just for fun.

The transformer is no more present, diode D38 is burnt.
The 12AX7 tubes are missing.
The led segment display is totally gone, no one of the leds are working.

I pulled out all the diodes from psu and slowly gave 8V DC, with a bench power supply, at the cathodes of D38 and D39.
The voltage regulators are working ok, giving me steady 4,9V at their outputs.
The current draw is at 550mA with a pair of new tubes in their sockets.
I saw, from the original ADA drawing, that the original transformer can give a maximum of 650mA. Is this current consumption right, in your opinion or Experience?

The clock signal is present:     12MHz    2,5Vpp (sine)   at the crystal
                                           1MHz     6Vpp  (square) at pin3 of U37
                                           2KHz     5vPP  (square) at pin12 of U36
                                         
The first thing I'm going to do is building a new display, since the original one is no longer available.
Does anybody know if the display is a common cathode or anode?

I'm more into vintage tube amp rstoration than digital units, so i will need a little help.

[Iperfungus]

Hi mate!
Welcome to The Depot.  :wave:

This is going to be a very interesting thread!  :thumb-up:
A very good start!  :bow:

I think you need MJMP's help here: he knows everything about these units and also has some original spare parts.

I will just sit down and watch with a bowl of pop-corn.  :banana:

PS. I just saw you're from Italy like me!  :lol:

[GuitarBuilder]

MarshallJMP will be your friend... :banana-rasta:

[MarshallJMP]

I just measured it and at 8V it draws 362 mA with NO tubes. The mp-1 I was testing had no tubeboard (it's in for repair).

The display is a common anode.But are you sure the display is busted? I never had a totally busted display. My guess is that the cpu doesn't start up. Do any of the leds in switches work?

Also the midi board has to be connected to the mainboard with that grey flatcable else it won't start. Then check if you have a 6 MHz clock signal on pin 6 of U29 (Z80) and that you get pulses on pin 16 (the interupt input of the Z80).Do you have movement on the data and address bus of U29?

[Iperfungus]

This thread is for DJC!!!

Hey bro...have a look...
There's a MP-1 in very, very poor shape here (= DEAD)...and someone will bring it back to life!
Never loose Faith!  :lol:

[SteveFuzz]

Hello MJMP, nice to meet you.

The one of mine draws 320mA with no tubes in the sockets.

Yes, the display is totally busted.
I've tested every segment with the multimeter and then, to be absolutely sure, with the ATLAS DCA75, semiconductor analyzer. Dead!

With the grey flatcable connected  I have 6MHz at pin6 of U29 and I  have pulses at pin16.

The leds on the front don't light up when I press a Button.

"Do you have movement on the data and address bus of U29?"
This is quite obsure for me at the moment :)

[MarshallJMP]

Ok current draw seems okay since your display doesn't work the current will be less then what I measured.

But I have my doubts that the whole display won't work. How did you test it with the atlas, did you desolder out of the mp-1?

[SteveFuzz]

Hello

I forgot to mention that the display were connected to the board with single wires and not with the two original flat cables.
This made me suspicious, someone has messed with the display before!
So I traced down all the pins, unsoldered all the wires and tested all the led segments one by one. With the multimeter in diode position all the segments show infinity in both ways.
Same results with the atlas DCA.

[SteveFuzz]

Here is the matrix of the original MP-1 display.

[MarshallJMP]

Well I never would use my atlas or a diode tester to test a display.I do it the old fashion way and put some voltage on it  ;D

BTW thanks for making the pdf file of the display.

[SteveFuzz]

Hello

I took advantage of being at home with the flu for designing the PCB for the new display and reading somenthing about the Z80 microprocessor. I've learned a little bit more about it.

Just few questions before I go on.
How do I check movements on the data and address bus, as MJMP asked me?

Should the front leds light up even with the display out of the circuit?

[MarshallJMP]

https://commons.wikimedia.org/wiki/File:Z80_pinout.svg     Here's a pinout of the Z80, A0 to A15 is the address bus, D0 to D7 is the data bus.There should be a lot of movement on those pins.You can also check the outputs of U42 and U43.These drive the display, the leds and the front panel switches.

[Dante]

I'm just sittin here like...

[Griphook]

+1  :o ;D

[Iperfungus]

What about this???  :dunno:

:banana-upsidedown: