prophet 5 common problems

[mother_fox]

Hi, I bought a dead Prophet 5 and I want to restore it. Where do i look first? what is the most common problem for a Prophet 5 faliure?

[cornutt]

I'm far from a P5 expert, but I understand a lot of them had iffy power supplies.

[Steve Jones]

Can you be more specific? Do you mean that you plug it in, turn it on and there is no light on the front panel or on the power switch? Does the "tune" LED come on at all?

[Maschinengeist]

Pretty vague.

Sure thing, the power supply is always to be checked. Same with the outputs for hisses, hums, distortions. Calibration too.

It'l be far more easier to know the issues that to dress you up a dress of what could possibly be wrong.

[mother_fox]

Nothing happens, no leds, nothing, except that the back of it where the power supply is mounted gets realy warm and alot of noice is coming from the out put. so it's probably the supply.
appart from that, do you think i will encounter any other form of common problem, once i've find out what's wrong with the power?

[hfinn]

Shrug. I would worry about the Power supply first. Disconnect all the boards from the PSU and then test it and see if you are getting the proper voltages out of it.

[Steve Jones]

I would start by checking to see if there are any short circuit tantalum capacitors in the machine, particularly in the power supply. I would recommend replacing the PSU tantalums anyway.

[sussmayr]

Okay,

First off, as recomended, Power Supply issues first. Check the 15 v and 5 v outputs and adjust the 15v

2nd - If this is a Rev2 or older the LEDs will not kick on if the analog section cannot be tuned. That is: if a VCO is so whacked out, or dead, you will not get LEDs.
Now there is a technique where a steady tone is fed to the input of a comparator stage to fool the P5 into thinking it is tuned succesfully, then the oscillators can be dealt with. The service manual outlines the theory of this. SCI techs also used a jumber jig to run the computer without the analog board attached to troubleshoot CPU Board issues.

3rd - If the computer logic or a ROM is dead. hhmmmmm.... Older P5's have the OS sread across 3 ROMS! A friend of mine recompiled this code to fit on one more modern device. You would need a ROM burner if this is the issue.

I have a Rev2 on the bench now and I am living this reality. I will post some advice as I cross several bridges and have more clear answers to life's little problems.

[Steve Jones]

Also be VERY careful to make sure that you have the correct version of the manual for your machine when you work on the PSU. Although it was a bigger problem with the Prophet 10, some of the supply voltages screened onto the PCB may not be what is actually meant to be there, so refer to the service manual.

[mother_fox]

So if I have to change the supply I need to get one with output 15v/5v?

I've got one manual for rev3, is ther anything else apart from the PSU that's different?

[rjd2]

REPLACING the PSU would be 10x harder than fixing the old one. as you have already switched it on with all the circuits connected, the odds you are JUST NOW going to fry any chips is low.

im assuming the PSU is +/-15V and a +5V rail for LED's. i could be wrong. i do remember that it has a massive screw-in capacitor, i was able to order this from mouser.

1st thing you need to do is to measure those 3 rails and see what they are putting out.

lastly, if all of this talk in this thread is sounding like greek, it'll get fixed quicker at a tech, for sure. im not discouraging you from taking it on, just saying that if all you want is a synth that works, you're better off dropping 300-500 on repairs than spending months getting acclimated to this s**t.

[carbon111]

Besides the power supply, IIRC, The DAC and MUX have a tendency to go wrong on the P5. Worth checking at least.

They're hard to find replacements for too.

Vintage Planet carries some hard to find parts...