Trouble with an HY-5500 CRT -- HV supply not working - Videokarma.org TV - Video

user1 · #1 10-02-2023, 06:14 PM

I just bought a ToteVision HY-5500 portable television from a thrift shop, and it's not working. When connected to the required 12V, from an adjustable power supply, it initially draws about 70mA, then drops to about 50mA over the course of a few seconds. The tube is in good cosmetic condition, the filament lights, but no picture shows. I can't hear the characteristic flyback whine. I assume the step-up circuitry is to blame, but I don't know how to fix it. Can anyone help troubleshoot this problem?

user1 · #2 10-02-2023, 08:29 PM

It will now turn on for varying periods of time, from a few seconds to a few minutes, before shutting back off. This only occurs when brightness is at maximum. In the attached video, I adjust the Vertical Hold, which occasionally affects the picture.

A video of it in "operation" -- https://youtu.be/ZniLTqVYwkQ

Alex KL-1 · #3 10-03-2023, 09:19 AM

Some things come to mind:

I have seem some 5" CRT TV with strange sympton, and resulted to be only the ON/OFF switch, with intermitent good/bad and resistive contact.

Maybe a bad cap near to sweep dedicated IC, or bad solder?

Or, the IC...

In any case, track down the 12V input and check the switch; they can love to have bad habits

user1 · #4 10-07-2023, 11:15 AM

Quote:

Originally Posted by Alex KL-1

Some things come to mind:

I have seem some 5" CRT TV with strange sympton, and resulted to be only the ON/OFF switch, with intermitent good/bad and resistive contact.

Maybe a bad cap near to sweep dedicated IC, or bad solder?

Or, the IC...

In any case, track down the 12V input and check the switch; they can love to have bad habits

I'll go through and find out what all the ICs are, then check the caps near the sweep generator. I did notice that one chip was partially lifted off the board -- It was still connected, but all the legs on the right side were barely going through the holes. Maybe that's part of the problem, I'll resolder that chip. I'll also check the switch, because it's a combination power switch/volume control.

zeno · #5 10-07-2023, 02:31 PM

Where to start

Look for cold joints around the HV & hoz drive.
I assume the bright line is the tuning bar.

good luck
73 Zeno

LFOD !

user1 · #6 10-07-2023, 02:40 PM

tuning bar is the orange hook on the far left of image 1

I pushed that chip in and switched out a capacitor that looked suspect, but it's still not working. I'll check for bad/cold solder joints, but the whole thing is sorta shoddy -- some of the components are installed at weird angles, which might cause problems. Also, the neckboard wires are routed really close to the board, so it's hard to see or work on some areas, especially around the flyback.

kf4rca · #7 10-07-2023, 03:34 PM

Check and feel if any component is running hot. And secondly, sniff around the board for any burnt smell. A good way to do this is with a short piece of rubber or plastic hose. Remember, Vinnie Barbarino once said, "up your nose with a rubber hose."

user1 · #8 10-07-2023, 04:25 PM

If only I had one of those flux vapor pens...

user1 · #9 10-08-2023, 06:21 PM

It's working a little better, but I think I have a general idea for what the problem is -- when it's first switched on, the high-frequency whine appears, but quickly drops in pitch. Sometimes, it stays for long enough that a picture (specifically, static) will appear, but it then will switch to that weird scanning pattern with the drop in pitch. The frequency will also sometimes jump and twitch around, along with the picture snapping from wider to narrower, sometimes with a bright vertical line in the middle. Thus, I think the problem is related to the scanning circuitry. I'll look into that part of the board more closely if I can find a schematic.

kf4rca · #10 10-09-2023, 06:50 AM

I think you've got a open cap on one of your supply rails. No decoupling. Horizontal getting into the vertical (and vice versa). Do you have a cap meter?

user1 · #11 10-09-2023, 09:10 PM

I don't specifically have an LCR meter, but I do have a multimeter that can measure out-of-circuit capacitance up to either 10 or 100µF. We'll have to find the supply cap, though, because I don't have schematics for the TV. I hope to eventually make some, in case somebody else needs to fix their HY-5500.

user1 · #12 10-09-2023, 09:50 PM

Just looked on Amprobe's website, my meter goes up to 400µF. Looking into buying an LCR meter, because they're just really useful to have. I think I'll go for Keysight, as Amprobe doesn't make LCR meters.

user1 · #13 10-09-2023, 10:38 PM

UPDATE -- I realized that I had the deflection yoke on sideways the whole time. That explains why the picture was all narrow, and why adjusting the vertical-hold changed the width of the picture.

Alex KL-1 · #14 10-10-2023, 05:47 AM

Hehe, things happen - well, now you have only the H bad behaviour?
Check if HOT (H. out transistor) becomes hot or cold when TV stops, and check it's PSU, if not collapses (or the oscillator chip PSU), if already not checked it.

user1 · #15 10-15-2023, 03:47 PM

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?