Toshiba 42HP66 No Video Has Sound

[Robb]

A neighbor gave me a Toshiba 42HP66 that turns on with audio but has no video. The Vs is 190V - should be 186V - and the rest of the voltages are within specs. There's only one Y-buffer which passes an ohm test so I can't remove one to see if the YSUS is good. There don't appear to be any bulging caps or burnt resistors or transistors. When I connect it to an oscilloscope the waveforms on the YSUS and XSUS have the same shape as shown below (YSUS, XSUS). I've only measured one other TV with my oscilloscope but with this one the scope captured what appeared to be a still, standing wave on the YSUS and XSUS when I turned the Horizontal Time/Div to .2mS/Div.

The YSUS was measured at 5V/Div & .2mS/Div. The XSUS was measured at 2V/Div & .2mS/Div both with 10X probe.

Typically I would assume the YSUS was bad due to the lack of video but since the XSUS wave looks the same Idk.

I'm wondering if the YSUS and XSUS waves look right and if the Vs being 4 volts above spec has anything to do with the video being lost.

[tom66]

Re: Toshiba 42HP66 No Video Has Sound

Higher Vs would not cause no image.
I've never seen a negative wave on the Z-sus output; please double check that you measured that correctly. If it is correct, it looks like there is no output from the Z-sus and the other wave is being capacitively coupled through (basically leaking through the other electode.)

[Robb]

Re: Toshiba 42HP66 No Video Has Sound

I remeasured the XSUS with 2mS/Div and .2mS/Div. and both with 2V/Div and got a similar result. For some unknown reason the wave freezes on the 2mS & .2mS/Div settings. I posted the 2mS/Div below. I moved the vertical position to 0V on this picture.

[Robb]

Re: Toshiba 42HP66 No Video Has Sound

Are the YSUS and XSUS supposed to be inverse waveforms?

I found a XSUS repair kit that contains seven capacitors that claims to fix "no picture has sound" issues but it says that if the fuse is blown - which mine is not - then you need to replace the IPM and the fuse. Does this sound right?

Perhaps I'm getting ahead of myself but considering the above capacitor possibility I tested the caps in circuit on the XSUS with a DMM in the ohm/diode mode:

250V 150uF - When I connected the neg probe to the neg pole and the pos probe to the pos pole I got OF (open circuit). When I connected the neg probe to the pos pole and the pos probe to the neg pole I got .583V on all the 250V 150uF caps (four of them).

100V 150uF - When I connected the neg probe to neg pole and pos pole to pos probe I got OF. When I connected the neg probe to pos pole and pos probe to neg pole I got 1.0V for an instant before it went to OF on one 100V 150 uF cap. However on the other 100V 150 uF cap when I connected the neg probe to neg pole and pos probe to pos pole I got 1.0V for an instant before it went to OF. Both caps read OF when checked the opposite of the above.

100V 68uF - When neg probe to neg pole and pos probe to pos pole I got OF. When neg probe to pos pole and pos probe to neg pole I got .478V on both caps.

Please forgive me if I'm way off base with my approach.

[Robb]

Re: Toshiba 42HP66 No Video Has Sound

I'm also getting a dim picture that slowly grows from right to left after I leave it on for a few minutes (1st pic). If I turn it off and back on after it's been on for a few the image comes back but with lines (2nd pic). I can't help but notice that the side of the screen that the image grows from is the YSUS side.

I also tested the XSUS IPM - according to CoppelTVRepair's "How to test STK795-518 YSUS IPM for defects" - and found no shorts. I wish I had an ESR meter to really test the capacitors.

[tom66]

Re: Toshiba 42HP66 No Video Has Sound

What you can try doing is unplugging the Y-sus and checking the Z-sus output with a scope. No image is expected. What scope waveform do you see?

Your symptom is common with Z-sus faults. However, the edge it glows from has no relevance. The scan electrodes from the Y-sus cover the whole display, and sometimes you can get odd patterns as a result of Z-sus failure.

[Robb]

Re: Toshiba 42HP66 No Video Has Sound

I unplugged the power from the YSUS and got no signal from the ZSUS. I plugged the YSUS power back in and got the same signal as in post #1 & #3.

There isn't much to the ZSUS on this model. I found two repair kits for this ZSUS. One had seven caps in it and the other had an IPM. If the IPM is good would it be probable that the four 250V 150uF caps and the two 100V 150uF caps are bad? They do have a very slight roundness to their tops. I've seen other caps look similar but comparing them the 150V 68uF they are visibly more round. Not sure if you can see it in the pictures. Maybe I should just remove the suspect caps from the PCB and try to check them with my DMM on the Ohms setting.

[tom66]

Re: Toshiba 42HP66 No Video Has Sound

First check the two fuses on the board. You have no output from the Z-sus, the Y-sus wave is just getting coupled through.

[Robb]

Re: Toshiba 42HP66 No Video Has Sound

With an ohm/diode meter setting the fuses are good. According to the literature on the ZSUS repair kit if the fuses are still good it means the IPM is still good but the caps need to be replaced.

[tom66]

Re: Toshiba 42HP66 No Video Has Sound

That's possible, though it wouldn't be the 250V caps. What do you see either side of each fuse to ground, voltage mode?

[Robb]

Re: Toshiba 42HP66 No Video Has Sound

Both sides of one has 60V and both sides of the other has 190V. Same as Va and Vs.

[tom66]

Re: Toshiba 42HP66 No Video Has Sound

OK. There's also a 15V input, and associated fuse on the board. Can you see those? Gold cap white fuse., surface mount.

[Robb]

Re: Toshiba 42HP66 No Video Has Sound

I found a white square ceramic-looking fuse with gold endcaps by the 15V input that has continuity and 5V. It's rated at 10A 125V.

[tom66]

Re: Toshiba 42HP66 No Video Has Sound

Can you see any other fuses for the 15V?

[Robb]

Re: Toshiba 42HP66 No Video Has Sound

I couldn't find any other fuses on the ZSUS. There were two boxes that said "For continued protection against risk of fire...." which had FS1 and FS2 and FS3 respectively. Those were the only FS points on the ZSUS and they were the ones I measured above.

[tom66]

Re: Toshiba 42HP66 No Video Has Sound

OK, I am trying to think of how to test the supply voltages to the IPM. There should be some surface mount capacitors with approx 15 or 18V across them.

[Robb]

Re: Toshiba 42HP66 No Video Has Sound

I found some 15V readings at four of the caps near the IPM. Two were surface mount and the other two were cylindars. All of the 15V caps measured 0V on the other side. Some of the other voltages from the caps near the IPM were 5V-0V, 190V-53V, 53V-0V, 10V-0V, 5V-0V & 15V-0V (oneside - otherside).

There were some surface mount caps under the heatsink that I wasn't able to measure.

The red arrows in my picture mark the 15V caps although one of the surface mount caps can't be seen in the photo but you can see it's PCB #C47.

[tom66]

Re: Toshiba 42HP66 No Video Has Sound

Well, you appear to have all voltages going to the IPM, yet no output. It is possible the control board is not sending the signals to the IPM. You could test the outputs from the control board (going to the Z-sus) to check if this theory is correct.

[Robb]

Re: Toshiba 42HP66 No Video Has Sound

The voltages going into the ZSUS from the Control Board were as follows:

Wire - Volts
#1 - 1.1V
#2 - 0.0V
#3 - 2.7V
#4 - 1.5V
#5 - 0.0V
#6 - 0.4V
#7 - 0.0V
#8 - 0.7V
#9 - 0.9V
#10 - 0.0V
#11 - 15.3V
#12 - 15.3V

Point - Volt
OE - 0.3V
Zbias - 2.7V
Sus_dn - 1.2V
Sus_up - .7V~.4V
ER_dn - .7V~.4V
ER_up - 0.5V

The Wire/Volts were taken directly from the wires going from Control to ZSUS. The Point/Volts were found right next to the unput from the Control Board and since they are found on the IPM I added them for reference.

Not sure if it's relevant but I tested the voltages without an video input connected.

[tom66]

Re: Toshiba 42HP66 No Video Has Sound

Sorry I mean test with the scope... but the very fact you have voltages on there means something is being sent.