[FIXED] Hantarex Polo 25" - Good Fuse, Have Yoke Chatter, No Neck Glow, No HV

[JoshCRT]

Pulled from a Killer Instinct that simply didn't turn on one day. Was working fine previously. No obvious noise, no smoke, no smell. When given power I can hear the degauss coil fire and after ~2 seconds I can hear yoke chatter (I'm assuming I'm hearing vertical deflection only). I haven't ran the monitor in this state for longer than 20 seconds or so.

I have tested/done the following:

- checked heater resistor (R35), good
- checked neckboard colour transistors, all good
- checked bleeder circuit, R235 was open, replaced
- checked D137, R234, R245, D134, D135, all good
- checked T114 (HOT) in-circuit, tests good
- reflowed power supply section & flyback area
- B+ at TP6 is high, around 165vDC and continues to climb
- Replaced C114, no change
- B+ at HOT (T114) collector is identical
- IC104 pin1 reads less than 1v
- TP10 does NOT have 12v
- R189, R198 are good
- T108 and D129 test weird in-circuit, test fine out-of-circuit (compared to working chassis, these should test OK in-circuit)

That's as far as I got as I was called away. My next step is to recap the area around IC104 and work backwards from pin-1 to see why I'm not getting 12v.

[grantspain]

yes i think the missing 12v is key

[princess prin prin]

Without 12V you can't have deflection/high voltage as the IC (TDA2593) that sends out the time bases for horizontal and vertical deflection is supplied by 12V from the 7812 regulator that has 15V as input. If you don't have 15V the regulator is probably shorted.

[JoshCRT]

I recapped the entire chassis (all Nichicon or Panasonic, 105°C), resoldered D129 back in place and swapped T108 from my working chassis. I now have HV and a very nice image.

My B+ is stable, ~138vDC depending which test pattern is on-screen
The 7812 regulator is getting 14.96vDC
IC104 pin-1 is getting 10.83vDC

The input voltage to the regulator is about half a volt off from princess prin prin's readings. Hmm... Could be nothing but it may have something to do with my current issue.

Although the image is very clean/stable and all controls work, I'm sometimes getting a subtle whine, possibly also described as extremely rapid chirping. It's very quiet and seams to come and go (or gets really quiet so can't be heard over normal 15khz noise). I first noticed it after the monitor had been running for 30 seconds or so and immediately shut it off. I thoroughly inspected all my work, gave everything newly installed a little poke or wiggle and couldn't find anything amiss. I also double-checked every cap's value and orientation against my working chassis.

I haven't ran the chassis for longer than a couple minutes. The noise seams to disappear as things warm up, but after a quick power cycle it immediately returns. Being so high-pitched, it's extremely difficult to pinpoint what area of the chassis it may be coming from.

[grantspain]

that is likely to be the lineraity coil and is pretty normal on these chassis, if it annoys you then remove the coil and spray some insulation laquer onto the wire part of the coil

[JoshCRT]

This monitor is now 100% fixed.

I gave covering the width coil in laquer a shot. I'm not sure how much of a difference it made but there was still some sort of faint whining that would come & go. I spent some more time poking various parts of the chassis while running and determined it to be the flyback. Applying minor pressure to the area between the Screen & Focus pots caused the faint whining to change tone & volume.

Swapped out the flyback, chassis is quiet (as quiet as a CRT can be). Ran it for 8+ hours, no issues, still silent.