No lights, no display, no sound

[emunstar]

I've got a MP-1 that died on me a few years ago. I had it at a gig when the singer inadvertently killed the stage power while hanging a backdrop. The unit was on at the time but once the power was switched back on my MP-1 had no display, no light, and passed no audio. Looking inside I can hear the transformer hum and the tubes are glowing so there is at least power up to the tubes. Any ideas? The power was shut off and rapidly turned back on in a matter of seconds so my best guess is something on the unit has blown. Nothing inside appears burnt, there are no swollen capacitors or other visible signs of component failure.

[MarshallJMP]

If you have a backup of your presets you could try to pull the RAM chip out and back in,sometimes with a brown out the RAM can become corrupt,not always but i've seen it before.

But first can you measure the voltage over the 3 big caps near the power supply?

[emunstar]

Thankfully there are not any presets that I would mind erasing. I'll try pulling the chip. What are the voltages I should be seeing at the caps?

[MarshallJMP]

The 3300 µF cap should have 8 to 9 Vdc,the 2200µF caps should have around 20-22 Vdc

[emunstar]

The 3300 µF cap should have 8 to 9 Vdc,the 2200µF caps should have around 20-22 Vdc

To revive an ancient thread, I fianally got to test the caps and the results are

3300µF is 7.4vdc
2200µF were 23.2vdc and 22.9vdc......

[vansinn]

Wow.. talk about combined deja vous / flashback..

[MarshallJMP]

7.4V is quite weak, a 7805 5V regulator needs a 2.5V difference on the input.

[emunstar]

7.4V is quite weak, a 7805 5V regulator needs a 2.5V difference on the input.

Would you suggest changing the 3300µF cap?

Additionally, does anyone know the appropriate crystal to use should it need replaced? I attempted to measure its frequency and got nothing. I'm not sure if its faulty or my DMM just can't read it. If I'm reading the crystal right its 12mHz.

[MarshallJMP]

Well if the 3300µF cap is leaking then you should change it. Does it get warm?

Yes it's a 12MHz crystal. DMM's usally go up to 100kHz so best way to measure it is a scope. Also you could try to measure the voltage on pin 6 of the Z80, in theory you should measure 2.5Vdc (maybe less).

Try to fire the unit up without the tubes in it, see if it will start.

[emunstar]

I have tried to fire it up with the tubes in it and it did not start up. I've also tried to get it to start by rapidly switching the power on and off to no avail.

I'll feel the cap and see if it gets warm.

Funny thing, I just noticed that there isn't a battery in the unit either.

Question on the crystal, will any 12mHz crystal work our is it like a capacitor in that you need a few parameters matching like farad and voltage?

[bunkyloo]

I have a unit with the same issue exactly. Where is this crystal located?  I tried to fire up both ways . The tubes do glow . Looks like same issue possibly. Thanks Steve

[emunstar]

I have a unit with the same issue exactly. Where is this crystal located?  I tried to fire up both ways . The tubes do glow . Looks like same issue possibly. Thanks Steve

It's circled in yellow on the attached picture. Right side of the main board.

[MarshallJMP]

Check if you have 5V on pin 26 of the Z80.

[bunkyloo]

I did manage to check my caps the 3300 was 11.25 vdc and the 2200's were22.3 vdc and 22.7 vdc.
Pin 26 on the z80 was 5.11 vdc and pin 6 was 1.6 vdc. I should also mention I see a quick ADA logo and sometimes version text  only for a split second when I power off and it looks like a September of 87. I guess anything could be wrong.
Any thoughts ? Thanks Steve.

[bunkyloo]

Emunstar any luck with you're findings ?