Peavey DPM 3se power problem

[gizmouk]

My friend asked me to take a look at his Peavey DPM 3se Keyboard. All that happens is the lcd lights up and that's it. Peavey very kindly sent me all the schematics for the keyboard. I checked voltages on the power board at first and they read ok. But after taking a few components out and testing them, then putting them back in something has happened.
Before, the lcd looked clear so you could see the actual pixels. Now it looks kind of blurred. I have checked voltages and there is no +5V. I have attached the schematic of the power board with my notes on it. As you can see i trace the voltage at each component. Everything goes into a component called 'L296VR - U100). Could this could be the problem as output 2 is the rail to the +5v but it's outputting 0.13v.
Can anyone help and let me know if I've done the readings correct and where I should be checking?
Thank you.
p.s. I've also attached a photo of the top of the power board.

[stj]

Re: Peavey DPM 3se power problem

check if Q100 is shorted out.
and consider relpacing all the ancient small electrolytic capacitors - that chip is a switching regulator - they are fussy about such things.

[R_J]

Re: Peavey DPM 3se power problem

Check the components you removed, you may have either damaged them or maybe have shorted solder connections on a component you re-installed, The +5 volt line may be shorted somewhere loading down the regulator ic.

[gizmouk]

Re: Peavey DPM 3se power problem

Thanks for the replies.
I did a test on Q100 (SAC187) and attached the results.
I'll check the components I removed later tonight.
Thanks.

[gizmouk]

Re: Peavey DPM 3se power problem

I checked everything and I had diode CR100 the wrong way, doh!!!
The display is back to being clear but still no letters etc on the LCD, no sound. I'm leaving it on over night as I've read a few times when putting in a new battery it gives a blank LCD. So overnight charges up and then you reset the keyboard. So lets see what happens tomorrow

[gizmouk]

Re: Peavey DPM 3se power problem

Next morning is here and still the LCD is blank. I looked at the rest process and it asks to press 'multi' but that is on the display so I can't reset it. I'm next looking at another board by the outputs. I noticed that when I power off it does send a signal through the headphones.
Question. How hot should capacitors get? Should they roughly be the same as one of them is hotter than the rest. Thanks

[stj]

Re: Peavey DPM 3se power problem

do you have full schematics and not just the psu?

[gizmouk]

Re: Peavey DPM 3se power problem

Yes, Peavey sent me all of them.

[stj]

Re: Peavey DPM 3se power problem

well sharing would help.

[gizmouk]

Re: Peavey DPM 3se power problem

I did think that I replied on my phone and it wouldn't let me attach the pdf's, sorry. I'm home now and on the computer so here they are

I've noticed if I pull out chips the power transformer starts to humm and the lcd goes blurry again. The lcd is now clear but there is no text at all. As though the power is on but then the keyboard for its first stage but then stage 2 it does nothing.
I appreciate any help given. THank you.

[stj]

Re: Peavey DPM 3se power problem

hm...
2 processors combined with crap schems that you cant read properly.

i'll start by saying this: if you dont own a high-speed logic probe or a scope your limited to recapping the psu.

that said, the psu looks like something from the 70's and this system is going to be power-fussy.
so re-cap the psu with panasonic FR series, and also maybe anything on the logic boards.

thee are reset circuits for the cpu's somewhere, and they wil use a small cap to kickstart the system.

[clearchris]

Re: Peavey DPM 3se power problem

The peavey equipment from the 70s were built like tanks, and the company is a joy to work with. I had a cap go out in one of my 70s rackmount amps. Peavey actually stocks repair parts, and ships them out pretty quick.

If it turns out to be an obscure part that busted, dont hesitate to call and ask about buying a replacement part.

[stj]

Re: Peavey DPM 3se power problem

this is late 80's - early 90's because it has a 68000 16bit main cpu.

[Longbow]

Re: Peavey DPM 3se power problem

Would someone kindly point out which part of the schematic shows the LCD? Sorry I could not pick it out of the maze. Given the complexity of this unit, my approach would be to identify a problem area before throwing parts at it for no reason. Fix the problem first, then decide if you want to restore it completely.

[gizmouk]

Re: Peavey DPM 3se power problem

Thanks clearchris for the info.
I now have an intermittent blurring of the LCD. Somewhere on the memory board must be something loose as one day its fine then another day after pressing some chips in its not. Also when I disconnect the leads from the power board to it the LCD is clear. The voltage output drops too when the blurring occurs. I think I pushed a chip in too hard so will take the board out and check the solder joints.
I'm looking at the micro board at the moment, the board just before the LCD. There are lots of zener diodes and a few capacitors. The capacitors are all axial, do I need to get axial or will radial be OK. The thing that worries me is the height.
As mentioned above the kick start isn't happening. I've disconnected both memory boards and still nothing.

[stj]

Re: Peavey DPM 3se power problem

radial caps are fine - it's only the shape that is different.

[Longbow]

Re: Peavey DPM 3se power problem

Well, if you are missing +5, then I guess the first step is obvious. Most likely things will come to life again. My thought was that in the absence of a clear problem, your LCD should at least display a cursor or an all-segment test pattern. I see the supply uses a protective crowbar on the +5 - you don't see that very often. I suppose every IC in the unit would be smoked if that voltage happened to rise.