Trouble with an HY-5500 CRT -- HV supply not working

[user1]

Also, none of the chips get any voltage on their VCC pins when the TV is not displaying.

[user1]

Why did this thread abruptly stop? Is there something irreparably wrong with the CRT?

[Alex KL-1]

Originally Posted by user1

I just made a discovery -- when the base and collector of the HOT are shorted momentarily, the TV will display various forms of the usual scan pattern, and sometimes even a mix between the scan pattern and static. When the TV is not displaying, the base is at +12V, The collector is open (connected through a capacitor, specifically) and the emitter is at +12V. I think this means that the PSU for the transistor is bad, correct?

About the terms, for not confusing... The "HOT" you cite here, is the one with heatsink? Normally the one we call "HOT" is the horizontal output, and this is the directly connected to flayback, and will not show the behaviour you described (then will be the regulator transistor). And in most little TV's the HOT don't have heatsink.

It seems to really have some PSU regulator bad behaviour. Also, Indeed, the main transistor regulator can be open (the transistor you shorted the B-E), or some near it. You can remove the transistors for testing with DMM in the diode scale, to be absolutely sure.

Is good to find the schematic for the TV, or, in the absence of, you can dowload every IC datasheet to study them and plan some tests (to be sure none contribute to the regulator or control it).

[Alex KL-1]

Originally Posted by user1

Why did this thread abruptly stop? Is there something irreparably wrong with the CRT?

For example, in my case... Too busy last times... is easy to miss to respond to some topic/thread, and then this vanishes from the list, unless the ones can respond to it manually subscribe to it, or maintain the thread windown open (I noted that the Videokarma don't automatically subscribe to the thread when one post something). So this ends lost, until the therad owner quests about/bump it.

[Alex KL-1]

Originally Posted by user1

Why did this thread abruptly stop? Is there something irreparably wrong with the CRT?

If you have a full raster when you short the PSU transistor, the CRT have to be good, in principle... unless it have a yoke problem, but then it will distorts a lot the image or shrinks it.

[user1]

I've tested many components connected to the HOT and power supply transistor, as well as the transistors themselves. All components tested are in good working order. At this point, I think the driver/generator chip might be bad, so I'll order a replacement and see if it works. Before I do that, though, I think I'll test all the other transistors on the board, in case one's bad.

[user1]

All transistors are good.