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 ½ 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 ****.

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

OK, I have made a few discoveries. This is a PRO-76.

I beat it, the set is up and running. As usual for a Pioneer this age
it was in video mode and I had to put the two caps in the IF assy. Then
to boot it has no sound. Blown 4280 and a 4 amp fuse. Plus the green
tube is a bit soft.

I am really starting to think these sets are a bit too old. Next we'll
be looking for a greem tube. That's OK, especially if we can find one.

But people fall in love with them, the shiny black cabinet, the style
etc.

The 2.2s off the PNP transistor to the left. I swear I checked them.
Paerhaps the first 3451 I had was bad. This would not be the first
time. The .33s were replaced with a higher wattage. There is nothing
unsafe about this if something is designed on this planet. Hmm, perhaps
I should go back and, oh screw it.

Pioneer has certainly pioneered in wierd designs.

JURB

PS, still want to know about those jumpers.

JURB