Need schematic of HP 8591E (859X series) CRT module (Omni Vision LP0615E3Y)

[carl_lab]

Can somebody help?

[Daxxin]

There manual service of panasonic video module 859x ko4bb manuals etc if i can remember sm601 or like that maybe is similar?

[carl_lab]

That's a very similar looking module (maybe they are even interchangeable on module level):
http://www.ko4bb.com/getsimple/index.php?id=download&file=HP_Agilent/HP_8595X_Video_section_TR-60S1A_from_Panasonic_Operator_Manual-HP859X_module_video_panasonic_SM.pdf

But unfortunately it uses other ICs (AN5763 + AN5790) instead of TDA1170S + TDA1180P.
So schematics will be different.

What voltage could I expect at brightness potentiometer? (I don't want to kill my multimeter...)

Screen stays completely black; filament is glowing dark orange.

Any hints, I could check?

[Daxxin]

Dont know if interchangeable one of them is 15khz rate horizontal sync and the other one 19.2khz but i guess working ..
What about rear composite out? Working?

[carl_lab]

What about rear composite out? Working?

I think so, but I've not checked that.
I've exchanged the complete CRT module, and with the other module it worked.
Now I have to repair the defective module, because the 2nd (working) module isn't mine...

[james_s]

Most small CRT monitors are more or less the same, so if you can find a manual for a similar monochrome monitor you'll probably find the voltages are very similar. Heater is almost always 12V for small neck CRTs and the larger neck tubes are normally 6.3V. Focus is the only voltage on the neck you have to watch for, that can be close to 1kV depending. If you have EHT you should get some static on the face of the tube when powered up, or you can check by shutting off the power and then poke a grounded screwdriver under the anode cup and it should discharge with a snap. If you have EHT, you can try momentarily grounding the cathode pin on the CRT and the screen should light up with a raster and bright retrace lines. If that doesn't happen, check the G2 (sometimes called screen grid) voltage, it's normally 100-300V or so on small monitors. If it is too low you will get nothing on the screen.

[SaabFAN]

Isn't there a LCD-Modification available for these instruments?
Might be worth a look if the repair becomes too complex.

[carl_lab]

I didn't find an LCD conversion kit.

But I found a nice schematic (with voltages !) of a similar monitor using same TDA-ICs:



Max. voltage at brightness potentiometer was too low (about -20V instead of about -80V of the working unit, IIRC).
I will verify at monday, when I'm back in the lab.

[james_s]

I never liked LCD conversions anyway, CRT looks much nicer IMO and when converting an existing instrument you don't get the big advantage of LCD, a much more compact instrument.

[carl_lab]

I also don't like LCD conversion kits very much, but they have at least one advantage:
they don't burn in.

[james_s]

They are also still manufactured, that's another big advantage.

For hobby use though a CRT should last many years without burning in, usually the tubes you see with a lot of burn were left on 24/7 and/or run with the brightness and contrast excessively high. Turning down the contrast a bit in particular will greatly extend the life of a CRT, less pounding on the phosphor and less wear on the cathode too. A good quality CRT will go 30,000-50,000 hours before it starts to look tired.

[Daxxin]

I like lcd conversion wish i can do that to my 8593A , but need to find a right one scan converter  mostly working at minimum 31.5 Khz
and real-time interpolation scan converters very expensive.

[james_s]

Why would you want to? Added complexity, crap contrast ratio, lower apparent resolution, poor viewing angle, from a performance standpoint LCD has few advantages and many disadvantages. The only real advantage in a retrofit is availability and slightly improved geometry.

[carl_lab]

Update:
voltages at TDA1180:
pin 2: working unit: 4.97V, defective unit:8.98V
pin 5: working unit: 7.40V, defective unit:8.68V

I swapped horizontal final stage darlingtons BU806 from working unit to non-working unit and vice versa.
-> No change. So darlingtons are working both.

Waveform at darlington's collector (line transformer primary and horizontal yoke):



(That's 2 waveforms stacked: 1 high peak per 3 divs period is working unit, 4 smaller peaks per 3 divs period is defective unit).


Then I measured voltages at brightness control potentiometer:

defective unit: -2.2V/-19.5V/-19.5V at left stop, -1.8V/-1.8V/-19.7V at right stop (orange/yellow/green cable)
working unit: -10.9V/-77.5V/-77.5V at left stop, -9.3V/-9.3V/-78.9V at right stop (orange/yellow/green cable)

That correlates to the waveforms, peak amplitude at defective unit is about 1/4 of working unit.

Then I thought the CRT may have a short, so I removed the plug from the tube neck, and after a few minutes, voltages at the brightness pot rised nearly to the normal values, and I was looking at the waveform I checked before: it was slowly transforming from the defective waveform to a waveform nearly the working one.
I set the plug back to the CRT neck, and when I looked at the screen, the picture was back!   

What's that?
I tried a little knocking and coolant spray to reproduce the failure, but it wasn't reproducable.
Focus is not as good as the working unit, focus control pot has no effect.

Next, I re-soldered suspective solder joints and washed the pcb with IPA.
After that, I switched the SA on, and the failure was back (no visable picture). 

I removed the CRT neck plug and waited a minute or two. The voltages at brightness control stabilizes near normal values, then I put the plug back to the CRT neck, and picture is back!
That's absolutely reproducable!
To get the picture back, you have to remove the plug for some time to build up normal voltages at the line transformer's secondary side, then reconnect the plug!

What the hell could be the root cause for that strange behavior? 

[james_s]

It's possible that there is a short or open in the CRT itself, does the focus pot affect the focus voltage with the CRT unplugged? Do you know anyone with a CRT tester? I have a Sencore CRT analyzer but I'm not anywhere near you. Can you swap the CRT between the good and bad monitors to test?

[carl_lab]

No, I don't know anyone with a CRT tester.

I've thought about swapping the CRTs, let's see tomorrow...

[james_s]

It should be fairly simple to do, just leave the yoke on the tube and swap the whole assembly. Don't forget to discharge the anode lead before disconnecting and take care not to damage the evacuation pip in the center of the pins.

[carl_lab]

The tip of the defective unit's evacuation pip looks like a bit broken off.
But filament is glowing normal (orange color - not white for a second, and then dark forever) and the CRT is (sometimes) working normal, so vacuum should be intact.

[james_s]

If the vacuum was not intact you would know immediately. I once powered up a TV that it turned out had been damaged in shipping. There was an immediate lightning storm within the neck of the CRT.

[carl_lab]

Result of swapping CRTs: both CRTs are working
Result of swapping TDA1180: both TDA1180 are working

What possible root cause is remaining:
- line transformer
- secondary capacitors
- secondary rectifiers
- (something else?)

[Armadillo]

likely transformer few turns shorted/glued together.

[carl_lab]

Result of swapping CRTs: both CRTs are working
Result of swapping TDA1180: both TDA1180 are working

What possible root cause is remaining:
- line transformer -> No, swapped without change
- secondary capacitors -> No, swapped without change
- secondary rectifiers -> No, swapped without change
- (something else?) YES!

I replaced all electrolytic capacitors with new ones.
10th of 11 was the culprit. 
It's the 4.7uF coupling capacitor between TDA1180 pin2 to darlington BU806 base (C212 on schematic, C 14 on PCB).
It has only 0.8uF remaining capacitance.



2 other electrolytics were out of tolerance, but wasn't root cause of the main problem.

Thanks to all, that tried to help! 

[james_s]

Nice! I wouldn't have thought a capacitor would cause that particular problem, but I do usually shotgun the electrolytic capacitors when I repair a CRT monitor. I used to work on a lot of arcade game monitors and tired capacitors were very common in those. Glad to hear it's all working again.

[carl_lab]

Thank you!
If I'm honest, my first thought was "that's an easy repair, I'll bet that's an electrolytic cap". 
But then I tried it the analytic way. I measured waveform at TDA side of the culprit cap and at the darlington side. Both looked very similar, except the DC-offset. So I thought "it's OK, search for other suspects"...

[Curve514]

Sorry to revive an old thread but I wanted to say thank you!

I got hold on a HP8594E witha non-functionning screen and the problem was exactly the same capacitor as described here!

Thanks again!
Curve