Faulty Pioneer PX-7

Supporter (1)

15-12-2011, 17:45

hi guys

I've had this Pioneer PX-7 up in my loft for a few years. I picked it up at a car boot sale a while back, and it has never worked. I'm having a big clear out and so I thought I'd give it another chance, now that there are so many more people online that might be able to help.

Basically the unit powers up, but the video output just gives a black screen with a small amount of snow.

My knowledge is limited, but here is what else I know / tried

- pressing the video output switch, the machine makes a 'click' sound, which is presumably some kind of small mechanism that re-routes the video. So power is getting to this.
- I've tried connecting the video to the standard composite out, and also running wires from the monitor output (both give the same thing, the black screen with a touch of snow)
- I've plugged in a game cartridge which I know works, and this has no effect
- I've left the unit switched on for a number of hours, then powered off and felt the caps and chips on the top half of the board for areas of heat, and there are none, other than a bit of warmth on the shielding near the power supply, which I would think was normal.

So I'm pretty much at a loss. Anyone got any ideas? I'm in the London, UK area if anyone is closeby that might be interested / able to help.

thanks in advance - I could take pics of any area if it helps - the board seems clean though, no signs of spillage or areas of heat damage or anything like that.

Personally I think it might be one of the chips, but I'm no expert.

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Por Oscar

Guardian (587)

15-12-2011, 19:57

What version do you have? Japanese or european one? Because video and power are different. Do you have sound if you type something or when you put a game? I don´t know if there is an audio out connector, but if yes, you can test audio. If you have audio maybe there is a problem with video connector or cable. You can check the power suppy, under the pcb, because sometimes there is broken solder-pins and some voltage lines don´t work. Two days ago I have repaired a MSX that powers up, lights on but nothing more and was just this problem, easy in this case.

Por cklayman

Champion (294)

15-12-2011, 21:35

There is a somewhat similar discussion going on right now here: http://www.msx.org/forumtopic13837.html They have some suggestions there on how to establish what could be wrong with the computer.

Por RetroTechie

Paragon (1563)

16-12-2011, 00:12

Welcome at MSX.org, highrise!

Indeed check out the other thread, and (as far as you can) try diagnostic checks suggested in there. When I repair an old machine, basic procedure is:

Thorough optical inspection of power supply / mainboard, looking for things that have obviously blown up, cracks in circuit board traces, unplugged connectors etc, anything that doesn't look right. For things that come as "condition unknown" from eBay etc, this is standard procedure for me. First check inside, then try to power it up.
Measure supply voltages - any plain voltmeter will do.
Check if clock signal(s) are present. This is easy or near impossible depending on available tools.
Try to find out whether CPU is doing something. Again, available tools / knowledge helps a lot.
Do simple checks like those in above thread.
Plug in external RAM cartridge & repeat.

At this point I often have some good clues as to what the problem might be, and exchanging 1 or 2 parts usually does the trick. Only then I move onto video output, run test programs etc.

Por kwilting

Expert (80)

16-12-2011, 09:31

I had the same problem with my PX-7. It also made a buzzing sound when I powered it up. The problem was the big capacitor that had come loose. You might want to check this on your computer. Just open it up and look for the biggest capacitor in the middle. Normally it's glued to the board and soldered and the connectors. Good luck !

Por Oscar

Guardian (587)

22-12-2011, 21:32

For one strange reason I had more or less the same black-screen problem when I tested again my PX-7 (today). The computer video was not working but there was the relé noise. I have opened and I have resoldered the big capacitor (thanx kwilting) and the power line pins (the ones connected to the main board). Some resoldering from power button to main board too. Now is working ok. I have not seen any visible problem like solder-pin cracks but the capacitor had a strange and little dirty solder.