Cause for CRT Monitor Jittering?

[wasedadoc]

ok i will have to pull the board back out and then I can get you the  IC601 PN.
I don't even see the bridge rectifier looking at the photos I took...

It is the black square with the + and - written on it. Just to the left of the 20 Watt resistor.

[sideburn]

Ahhh right ok I will test it and see what the resistances are.

[sideburn]

OK guys I am back with some more results.

First, I pulled both the large c602 and small c603 and they tested ok from what I can tell ESR in range...
cap checker showed ocorrect  uf values... The two ceramic looking caps next to c603 and both reading open circuit with my ohm meter, not sure if thats normal.

The large ceramic resistor checks good as well.

But the bridge rectifier looks suspicious to me, when I check the 4 pins with my DMM in diode check mode, I am getting .5 or so one way between the pins and 1.8v the other way EXCEPT for the two pins that the mains is connected to fi i check THOSE two pins i get 1.8ohm + to - and 1.8ohms - to +.... only those two pins. all the rest give me .4 or .5 ohms one way and 1.8 the other.

** I think I may have been testing it wrong. Maybe those results are expected. Not sure if I should be getting 1.3v when i test pos to pos and neg to neg on the output side though... Should that be Open? starting to the maybe the bridge rectifier is actually ok.. hmm... if so maybe its those blue caps ceramic caps (c407 and c409)?

can I bodge a diode between those pins to see if it fixes it?

IC601 is a an STR 30135 (7317)

[wasedadoc]

Every bridge rectifier has four diodes and four pins. Two pins are the AC input, one pin is the +ve output and one pin is the -ve output.

Draw the schematic of the four diodes and the four pins on a piece of paper. It should be obvious to you how to check each individual diode.

[sideburn]

Yeah. I know what they are I jumped the gun on it when I tested. It seems ok to me the only thing is when I test the reverse polarity a am getting 1.5v and not and open circuit. But I’m testing in circuit so maybe that’s normal.

I don’t know. So far everything is checking out ok.

[wasedadoc]

Yeah. I know what they are I jumped the gun on it when I tested. It seems ok to me the only thing is when I test the reverse polarity a am getting 1.5v and not and open circuit. But I’m testing in circuit so maybe that’s normal.

I don’t know. So far everything is checking out ok.

You should be testing each of the four diodes individually, forward and reverse. Eight tests in total.

[sideburn]

Yes. I have. And I get .5v one way and 1.5 to 1.8v the other way on each diode.

[wasedadoc]

Take the bridge off the board and test it again to be sure.

[sideburn]

Take the bridge off the board and test it again to be sure.

Bridge checks out good out of circuit, so based on that and low ESR on the caps, nothing looks suspicious.
I guess I’ll replace them anyway and see what happens.

[floobydust]

Hum bars I've seen caused by:
1. the main filter capacitor low in value
2. degauss PTC thermistor bad (high ohmic value) starving the input voltage to IC601.
3. B+ voltage regulator IC601 STR 30135 which has a spec. 135VDC +/-0.8V output with 150-175VDC input. You could check the main B+ rail is in spec.

[sideburn]

Yea I can check b+ Once I find where to probe.
Was also wondering if I can somehow narrow it down with an o’scope by looking at the a/c waveform in different areas.

[sideburn]

Not sure if this is any clues but way back when this monitor started acting up it was more jittering than smoothly warping.

Here’s the first video clip: https://youtu.be/_FlFdDvYHpA

And here is it’s now again to compare: https://youtu.be/_liYw2lJrPc

[wasedadoc]

Yea I can check b+ Once I find where to probe.
Was also wondering if I can somehow narrow it down with an o’scope by looking at the a/c waveform in different areas.

Do NOT try to use an oscilloscope unless:

1.  It is running from batteries or, highly preferably, you have an adequately rated isolation transformer powering the TV.

2.  You fully understand how to avoid electrocuting yourself.

That TV's power supply has no mains isolation and no matter which way you connect the AC supply the chassis is never at neutral (or whatever it is termed in your part of the world).

Suggest you watch the EEV blog video

[sideburn]

Well I replaced the bridge rectifier, the large 330uf 200v cap, the 33uf and the 10uf and no change. If anything it may be worse.

All components I changed out are marked in yellow in the attachment.

[floobydust]

Yea I can check b+ Once I find where to probe.

What do you measure for B+? I think it's 135VDC.

[sideburn]

How do I locate B+ ?

[sideburn]

This spot has a “B” could that be it?

See attachment:

[floobydust]

Without a schematic or service manual, a repair can be very difficult. You really need an isolation transformer for safety when making measurements.
Also, it's a 'hot chassis' monitor yet somewhere the video input is isolated??? This doesn't make sense, is there continuity from the video input jacks to the chassis common? That's from the bridge rectifier (-) to the inputs. I can't see an isolator module. Hopefully your computers aren't getting a lift...

The output of IC601 STR30135 the +135VDC regulator goes to C519 33uF 160V, also needs C603 10uF to be OK, (both of which you say you've replaced).
You could carefully measure DCV at C519/nearby jumper, to the chassis common. If your multimeter is AC-coupled you can also measure ACV to see how much ripple is present.

I notice there is provision for a tuner? so this same chassis may have been a TV set, and sometimes used for bigger CRT's. So a service manual for a TV (vs monitor) or bigger set (say 15-17") can match a board sometimes.

I dislike the too much flux on the flyback transformer pads, I would clean with IPA/q-tip and scrape a bit and then let it really dry off. Some pins have 800V, 180V outputs which like to arc. Make sure the board dries out thoroughly.

edit: I did see another isolated small power supply for the video board I think. T401 and C416, with regulator Q416 C422, C423.  Check those caps.
Check R449 looks broken? It must be a high value part for safety I think. By connector A-6, it's between the isolated video and hot chassis common.
The other 9VDC power regulator for the (hot) video is C241, C408, C410 with Q241.

[sideburn]

Thanks I will check these next. I did check the voltage on the large white ceramic resistor and it is 135v on one side and 85v on the other.

[wasedadoc]

Also, it's a 'hot chassis' monitor yet somewhere the video input is isolated??? This doesn't make sense, is there continuity from the video input jacks to the chassis common? That's from the bridge rectifier (-) to the inputs. I can't see an isolator module.

In Reply #44, Andy2000 wrote:

"That monitor is based on a common for the era Sony 13" TV chassis without the tuner and IF components.  It uses a hot chassis with opto-isolators on the video input."

[m k]

Not sure if this is any clues but way back when this monitor started acting up it was more jittering than smoothly warping.

Here’s the first video clip: https://youtu.be/_FlFdDvYHpA

And here is it’s now again to compare: https://youtu.be/_liYw2lJrPc

From first video I'd say it's a cracked solder.

Second video can't be compared.
It's more like a locking, grounding or power issue.

Do a new video with same screen as in the first one, or at least something with black background.

Anybody tried finding a hiding crack with a laser pointer, how was it?

[floobydust]

Thanks I will check these next. I did check the voltage on the large white ceramic resistor and it is 135v on one side and 85v on the other.

I see a problem with those voltages on the big power resistor R606 200Ω 20W. One leg connects to the output of the bridge rectifier. I would expect at least 160VDC there.
Other leg goes to the STR30135 IC601 voltage regulator output, I would expect 135VDC there.
This makes me believe the circuit is starved and running at low B+ voltage, or more likely the readings are wrong.

There's not many parts that can cause this problem - open diode on the bridge rectifier D601, low value for main filter capacitor C602 330uF, high value for R602 is 2.2Ω and likely not to fail high value as a wirewound part, L601 also not likely to fail high ohms, on/off switch etc. and OP you've replaced those parts. The degauss coil and PTC is independent across the line, not in series as some sets do.

So it doesn't make sense which means the voltage readings are wrong or new parts are duds. OP do you measure voltage to earth-ground or the hot chassis common? Use the chassis (-) common which is the black wire on the backside as your reference point.

[sideburn]

Hmm maybe i mis-measured. I will make a new video shortly if the current condition. I’ll put a game on it with a black background and mount the camera on a tripod so it will be more accurate.

[floobydust]

Please check isolation resistance from the video input jack shell to the hot chassis(-) at that black wire on the underside.
The monitor has a "death resistor" that I can see, connected between the hot chassis(-) and the (isolated) video power - as it looks damaged. R449 by connector A6, I'm guessing it's 4.7MEGΩ carbon comp. Might be similar to R601 (near L602 and the bridge rectifier). I would say it's a safety critical resistor R449.

[sideburn]

OK new test results, new video and photos.

First off, I tested the voltages incorrectly across the ceramic 200ohm resistor (R606). I was measuring from chassis and and a/c neutral.
This time I pulled the board out completely, dropped the flyback anode into a glass container and powered the board up. I then measured D/C voltage from the - pin on the bridge rectifier to the resistor and measured 155vdc on left side and 136vdc on right side.

R449 is measuring 4.8M ohm (in circuit)
R601 is .9M ohm (in circuit)

c416,c423, and other nearby capos are all low ESR

New video: https://youtu.be/umTy5FhXovM