Pioneer RPTV SMPS

Don't have the model # handy, but for quite a few years these things stayed pretty similar. This one seems like it is right before the PRO series.

The question is more about the Pioneer SMPS in general.I'm wrestling with two of them right now. The one puts out about 20 volts instead of

135. That one can go by the wayside, it is older and not in as good condition, the other one is among the Pioneers we dubbed "precious". The ones with the high gloss black ( laquer ? ) finish. People love them.

The thing is blowing the chopper transistor immediately, within =BD a second. I found that if I jump the relays and bring the AC up slow on a variac it will not start.

So I am in a bit of a spot. No print of course, and I only have one

2SC3451(?) left.

Anyone who successfully troubleshoots this type of power supply; if you had one burning down immediately how would you proceed ? Is there a lightbulb trick or something for these ?

I have done a ton of cold checking of components in the circuit. Nothing pans out. Usually pretty good at flying by the seat of my pants, this one is proving to be a coorva. I thought I was onto something when I measured 119 ohms across a 100 volt electrolytic, but that was caused by resistors, not a fault.

This cold checking was also done before the parts were replaced the first time, the chopper, the two .33 ohm emitter resistors and a TO220 transistor which appears to be a current limiter. In the circuit the other transistor is near the 47uf/100 volt lytic so at this point I am thinking that since they have two 240 ohm resistors across it, it has something to do with slow start.

I am normally pretty good at working without prints, but Pioneers are a bit harder due to the way they mark the PC boards. What's more this condition destroys components. Is there a way to make this thing start on low AC so I can troubleshoot the feedback loop and cop a waveform off the chopper collector, things like that ? Or should it start on low AC but the last chopper shorting blew the drive circuitry ? As I said I have checked just about all the components in the area ohmmeter wise.

If nobody has any ideas, my next step will be to bring in the old Wavetek generator and drive the chopper myself. With the variac I should be able to go through the feedback circuit, or conversely if the thing won't get to 135 V output without blowing I can check for an insidious short not showing up during static tests.

Insidentally there is actually a fuse blown on the secondary side, but it is not involved in the feedback loop, only the 135 V line is. At this point I proceed on the assumption that it went overvoltage and caused that fuse to blow, and hopefully not much else. But I figure I'll deal with that once the PS is up and running.

I remember once I asked a question about a Pioneer and got an answer in hours, a 110K resistor open. I don't expect that here, I suppose it could happen but I don't expect it. If I can get a few specifics about this SMPS I can use it. Are they supposed to run on low AC ? If they have current limiting why did they bother to fuse almost all the secondaries ? If it doesn't have current limiting why the two .33 ohm emitter resistors ? It is certainly not class A.

Any info that might help would be greatly appreciated. I am not looking for someone to simply give me the answer, that might not be possible. Just something in the way of troubleshooting techniques would be fine. Someone must fix these. How ?

Another question that has burned in my mind ever since I worked on my first Pioneer, why do they install jumpers across a piece of foil on the PCB ? They have a foil an inch wide and have like four jumpers on it, not to anything else, just jumping the foil.

Logically this can only be some sort of EMI/RFI issue. As cheap as jumpers are, still why put them in if not needed ? And if it is an EMI/RFI issue, why don't other manufacturers have to do it ? Then, if they really have strived for the best design, the least emitting and most efficient, why do they fuse it so high that the .33 emitter resistors blow instead of the fuse ? I know, inrush, but that is easily solved. Let's face it, the only reason they put fuses in TVs is to prevent lawsuits, and once in a while to aid ASCs in troubleshooting. Look at Sonys, you used to be able to just short the HOT out with a screwdriver and when you removed it the TV would resume operating normally. Of course nobody liked those power supplies but they were relatively trouble free.

So I do understand why a manufacturer would like to have their product expensive to service, no problem. That still doesn't explain all those jumpers in the Pioneers.

You have a plane of copper conducting, four jumpers don't do shit.

Perhaps I need someone who understands EM wave propogation to explain it. Perhaps I need a Russian tech. They have been ahead of us for decades in the field, but I am not so sure it is in the design of antennae, IIRC it was other factors that gave them the edge. Things having to do with topography etc., dunno.

Whatever it is I would like to know. I simply don't see how four jumpers about 3/32 of an inch away from a copper conductor can do much good, unless we are approaching UHF frequencies. If the thing is chopping that hard to put out harmonics that high, perhaps a bit of inductance in the collector line would be better, or even a ferrite bead.

I just don't see it. It makes no sense.

Let's put it this way, yall bitch when someone comes in here saying "it keep blowin da fuse", well this is quite the opposite.

I am hungry for food for thought on both these issues, feed me !

I'll send beer if that'll help.

Thanks.

JURB