WG 19K7601 Will not "fill-in" green pixels, green drive and cutoff has affect

[Mauzy]

I have a 7601 that I recently did a tube swap on. Prior to the swap, I had a relatively decent picture (balanced color levels) but the tube was HEAVILY burnt-in. It was a Philips tube, so I bought a cheap used philips tv. I plugged it in in the store and got a nice, clear white snow and the green menu stuff showed up perfectly fine. After the swap, I have a ridiculously sharp picture, but NO green signal seems to be "drawn" I can turn up the green drive and cutoff to form a completely green screen, but no amount of adjustments can be made to get an evenly colored picture. The monitor was just capped by myself, I have tested all my wiring and even used an entirely different harness, and I have tried two different game boards with no changes. I have reflowed the signal input connector on the chassis and did not see any other connection issues.

Any ideas?

Here is a picture of the green screen test for the game currently installed. As you can see, NO GREEN.

EDIT: I can jump the RED signal to the GREEN input pin and get an entirely red screen on the green screen test.

BTW, I JUST capped this thing and theres jail bars?! Ugh...

[lilshawn]

check that the pin on the neck card didnt get bent over or broken


can you send both the old tube # and the new tube #s?

perhaps there is a difference in the neck pins between them

it's an A33X33E287..... type of number

[Mauzy]

The old tube is a Philips MV-A48ABK05X
The new tube is a Philips MV-A48AFN40X

All pins appear to be in good shape as well on the tube and the neck card socket

[MonMotha]

This sounds like it may be further up the chain, e.g. RGB amp.  Coincidence with the tube swap may be, well, coincidence.  Drive/cutoff having effect says the cathode drive is probably working.  To be sure, you could swap a couple cathode connections to the CRT, but that may not be easy to do.  Can you easily swap back to the old tube to see what it does?

[Mauzy]

I could swap back, but I kinda destroyed the purity rings on the old tube though (this thing was CAKED with mud and such, had to have sat outside at some point in its life). That won't mess with me too bad, will it?

[MonMotha]

Eh, it'll still run.  You may need to adjust the purity to something semi-reasonable to verify correct operation, though.

[Mauzy]

Alright, I did a quick swap back. Other than the tube being pretty weak in comparison to the new one, there is NO trace of green. All of the colors look exactly the same, including the green screen test.

Your speculation as to the tube swap being coincidental seems to be correct.

[MonMotha]

OK, for grins swap the green drive transistor with one of the good ones (red or blue) e.g swap Q201 with Q202.  I suspect no change, but that'll at least eliminate it as a possible failure.  My recollection is that they do overheat sometimes on the K7000 series as they are poorly heatsinked.

If that doesn't do anything, swap wires going to pins 3 and 4 of P201 on your neckboard (which should be a model P456 or P448 (should have the same component numbers), according to my schematic).  That should swap the blue and green outputs from the RGB amp located on the main chassis board.  If this fixes your problem, check IC1 (uPC1397C) and R31 on the chassis board.  If the problem remains, check R208, R211, and C202 on the neckboard.,

You can get a service manual here if you don't have one.

[Mauzy]

Outstanding! I'll be working on this the rest of the day, my results will be up within a few hours! Thanks for your help so far! 

[Mauzy]

Q201 and Q202 Checked out
Wire swap did show something- the blue test screen definitely showed signal changes (no signal when swapped, signal present when stock). The Green test signal still showed no signal when swapped, no signal when stock.

R208, R211, and C202 are all fine

[lilshawn]

those video amps are quite prone to getting zapped and a color going out on them.

but as luck would have it, lots of units use the 1203 chip.


EDIT

also:

the traces around the transistors have a tendency to lift and break especially if the transistors get tweaked, the legs push right through lifting the solder up and break off the trace right at the edge of the solder. it's herd to see but if you wiggle the transistors you can see it.

[Mauzy]

Is there a way to test the IC AT the IC?

BTW, mine uses a UPS1397C...

[MonMotha]

So with the wires swapped, a blue test signal showed no signal (should have been green) screen while a green test signal also showed no result (should have been blue) but stock blue works and green does not?

If I understood that right, the fault is probably the RGB amp IC1 uPC1397C but may be R31 (100 ohms 1/4W) combined with a bad green drive transistor.  MCM has the uPC1397 for $7.19: http://www.mcmelectronics.com/product/UPC1397  The drive transistor is Q202 2SC2068 also at MCM for 59c: http://www.mcmelectronics.com/product/2SC2068

Swap both the wires and the drive transistors to check.  Blue test signal should then cause green screen while green test signal will show no result.

You can test the outputs of the RGB amp IC.  Given that red works, easiest thing to do would to check the red output of the IC with both black signal and full red signal then switch to green and check for similar readings.

[Mauzy]

So with the wires swapped, a blue test signal showed no signal (should have been green) screen while a green test signal also showed no result (should have been blue) but stock blue works and green does not?

Stock blue is very, very faint but it seems to be there. Could just be the adjustments, but long of the short there is no green signal anywhere. When I did the wire swap, I had done it with the transistors swapped. (Swapped the transistors, no change. Then swapped the wires)

From what I can tell, that is correct. I'll test the amp today to make sure but sounds like I will be ordering that IC and a couple transistors just to be safe.

[Mauzy]

Alright, I replaced the video amp and the green drive transistor and...


NO CHANGE.

Well that wasn't expected... what now?

[MonMotha]

Check those resistors/caps I mentioned.  That's pretty much all that's left in the signal path.

[Mauzy]

Found an iffy looking looking trace coming off of the amp that I replaced, touched it up and I have green!!! This thing is really terribly out of adjustment though. Been working on it for a half hour with a Golden Tee board with nice color test screens and its still looking dull but theres hope! Thanks for your help!

[lilshawn]

3 cheers for bad PCB manufacturing!!!... Hip hi.... wait...

[MonMotha]

That'll do it.  Thank you again, Wells Gardner