I haven't had time to check the raster as of yet since I have been
working 7/12. I have adjusted the B+ voltage back down to 135V, which
you were dead on about, since it says "135V adj". This has brought the
voltage down on the Hot collector to 101V, from 119V. The darlington
reads 135V on it's collector, and 101V on both emitter and base
(crossed by a small diode). Looks like this darlington is supplied by
135V from another winding on the flyback. The darlington emitter ends
up at the Hot collector via low ohm resistors and a diode.

There are two test points on the board. Both say "PD 135V". I traced
this all the way to an 8 pin socket that says PD at this terminal.
Other terminals are labeled +25, -25, gnd, etc. I'm not sure what "PD"
stands for, but both test points read 0V. Both points are electrically
connected and tie to either the base or emitter of a small transistor.
The other two legs read right at 135V.

This may be normal since I have the power board on my dining room
table out of circuit. The rest of the set is about 15 miles away. I'm
not sure I mentioned this in the original post. You are exactly right
in this being a real mother to figure out. I have only been working on
sets for a couple years (self taught) and with this groups help, and
have never seen a power supply like this. I try to stay away from big
screens because of the hassle of going back and forth to the set. I
already have a 46" Mits in my kitchen that is trash since I can't get
a replacement tube.

Again, I will post follow ups as I get info. This set belongs to
friends that have seen better financial times, and I would love to get
this thing going for them since they can no way replace it. I'm
willing to bite the bullet on the majority of parts costs. My time
will be free as usual. Thank you for your input and interest.

Hmmmm, what model of Mits and which tube ? We've had a couple with
really bad coolant leaks and the tubes are just fine.

Thing is, on the Pioneer, 101V might be right, you need other
observations to determine that. Can you determine if it has seperate
HOT and HVOT ? Look at the yoke plugs. Where the red wires went they
are all hooked together. Do they go to the flyback or not ? Sometimes
they go to a somewhat smaller transformer.

Now lemme tellya something about electronic design. They do not use a
darlington because they want to feed it with a high current source.

When you start finding your way around that board, in the PS there is
a darlington, and it breaks the rules. It is fed with a low impedance
source. But that is the exception. Normally darlingtons are used
because of lower drive current requirements. That means usually, if
your DVM reads 0.468 E to B forward, something is wrong. Pioneer has a
habit of using these 2SD12 somethings, and in some cases you can just
throw a 2SD401 in there, and in others you can't. And it is very
difficult to tell without a print.

Also, inspect that board very carefully for bad solder joints. More
than one have been fixed by simply resoldering them. Of course it is
still $300 because it is such a bitch to do, but actually those sets
are relatively reliable.

JURB

On Jul 23, 10:00 pm, wrote:
Hmmmm, what model of Mits and which tube ? We've had a couple with
really bad coolant leaks and the tubes are just fine.

Thing is, on the Pioneer, 101V might be right, you need other
observations to determine that. Can you determine if it has seperate
HOT and HVOT ? Look at the yoke plugs. Where the red wires went they
are all hooked together. Do they go to the flyback or not ? Sometimes
they go to a somewhat smaller transformer.

Now lemme tellya something about electronic design. They do not use a
darlington because they want to feed it with a high current source.

When you start finding your way around that board, in the PS there is
a darlington, and it breaks the rules. It is fed with a low impedance
source. But that is the exception. Normally darlingtons are used
because of lower drive current requirements. That means usually, if
your DVM reads 0.468 E to B forward, something is wrong. Pioneer has a
habit of using these 2SD12 somethings, and in some cases you can just
throw a 2SD401 in there, and in others you can't. And it is very
difficult to tell without a print.

Also, inspect that board very carefully for bad solder joints. More
than one have been fixed by simply resoldering them. Of course it is
still $300 because it is such a bitch to do, but actually those sets
are relatively reliable.

JURB

Thankyou again for your help. As far as the Mits, model #WT-46807.
Kept going into shutdown at power up. Can hear and see sparks flying
inside the neck of the red tube. Disconnected the anode and the set
stays powered up fine. No evidence of coolant leak that I can see. I'm
assuming a crack or something in the tube, but if a coolant leak could
still be the culprit, I would be really interested in how to fix this.
So would my buddy who is without it now! Either way, no big loss since
he got it free from a friend who was going to trash it (set was dead,
replaced pico fuse in vertical? supply), and worked perfect for about
a year until now.

Now the MOFO, the three tube yokes go to another component (trippler?)
and from this to the flyback. I checked the darlington that I
replaced, got 0.90 drop E to B. I'm again assuming this was probably
good, but not knowing I replaced with a sub - NTE2547. Of course got
the exact same readings and results.

I have seen numerous suspect solder joints under the magnifying glass
and hit them all. Haven't finished the entire board yet, but did flex
it in circuit with no effect to the tubes (raster) brightness. I
figure I am getting a clue to the problem when I touch a particular
diode off the flyback (with positive lead of my fluke) and can make
the raster brightness flicker brighter on all 3 tubes. I resoldered
and checked this diode good, but get the same results.

If you are looking for more clues or have other questions, please feel
free. If I don't hear from you, I will do as said and post updates as
I get them. Just don't know how long I will be stuck working these
damn 7/12's. Thanks a ton.