Bestech btm-19cm/bt-19 HOT/Flyback issue?

[SpoonyBard]

I picked up a pair of Bestech btm-19cm chassis listed as not working. I'm aware of the negative sentiment about these, and I am sure it has been earned, but the price was right for a couple of project pieces to learn on.

I recapped one chassis with the exception of a few caps on the neckboard that I had no replacements for.

I hooked it all up, got neck glow and a picture. But the image was not stable. I adjusted the v-hold and h-hold and managed to get it steady.

The image was bright and the color was good, but the horizontal width was too large. I adjusted h-size to the smallest I could get on the pot, but it was still slightly too large. I did not adjust the coil.

Suddenly the picture and neck glow stopped and I was greeted with a clicking noise. I believe that this is a protection circuit? Subsequent attempts to turn the monitor on have been met with the same clicking.

Does anyone have documentation on this monitor? In my reading it looks like this may be related to a bad flyback or Horizontal Output Transistor. I have not had much luck searching the part number for this flyback. How would one go about finding a compatible replacement?

 

[SpoonyBard]

Tested the other chassis without a recap. No noticable neck glow, but a very faint picture with an occasional cracking noise (arcing?).

Swapped the c5298 transistor (HOT?) and horizontal width coil into the chassis making the clicking noise. No change.

Swapped the flyback. No change.

Tried the other chassis. Heard the monitor pop on. No picture. Tried adjusting brightness, then the monitor shut off and started making a chirping/clicking noise. Shut down and retried and it now makes this noise whenever it gets power.

Looking for any direction into what to possibly test next. Flybacks seem impossible to source, so hoping to rule put every other possibility before giving up and shelving these. The tubes are really clean and the one had a great looking picture in the seconds it ran. Would be a shame to have them wasted.

 

[SpoonyBard]

Found a good deal semi-local for a different chassis. Picked up a Torvis mtg-2901cn (1901cn? Chassis has both markings) with an original yoke. This tube (a48krd82x02) seemed like a good swap for it.

The current yoke on the tube is a dse-1992nl measuring 13.5/1.8 ohms.

The yoke that came with the chassis id a dse-1992ub measuring 14.5/2.2 ohms.

I would really like to avoid swapping the yoke if possible. Is this close enough to run without risk of damaging the chassis?

 

[Kidkaos]

If you're at all interested in selling one of the neckboards, please let me know. I have a nice one that I couldn't repair the neck board but picture was beautiful on it before neckboard cracked in half.

 

[SpoonyBard]

Absolutely. Sent you a pm.

 

[SpoonyBard]

Checked the heater voltage and pinout of the original tube (a48qad220x) and it seemed like everything should be good. Decided to let it rip and threw the chassis in.

I get neck glow, but heard some arcing and could not see a picture. Cleaned the anode cap and the arcing calmed down significantly.

Still could not see an image. Adjusted screen/brightness/contrast and did not get an image. Decided to adjust focus on the flyback and found that the image would appear bright and gradually fade out over 1-2 seconds. Assuming that the flyback is bad. Going to order a cap kit and flyback for this today.

Horizontal is far too wide even with h-width at its lowest and vertical seems to tall as well. Going to go ahead and swap yokes on this as well.

 

[SpoonyBard]

Swapped the yoke tonight and things look a bit better as far as picture dimensions go. Still need to dial it in, but i need to get a consistent picture first.

Adjusting focus on the flyback displays an image that fades to black. I have a new flyback on the way, as well as a cap kit, but I wanted to see if anyone else has seen this issue before to know if I am on the right track.

 

[SpoonyBard]

Took a video of the issue at hand:
https://vimeo.com/864256641?share=copy

 

[SpoonyBard]

Found this in archives of the Bestech website today looking for more information on the Bestech chassis. Haven't seen this part list posted anywhere else, so i'm leaving it here in case it is useful to anyone else.

 

[SpoonyBard]

Installed the new flyback and the screen still shows no picture unless the focus is adjusted. It stays on longer and is brighter, but still fades out gradually after the adjustment is made.

 

[SpoonyBard]

Replaced all the caps and reflowed the input pins. Monitor came up and the picture stayed on screen. Color is off and needs some ring adjustments.

No red color at all. This chassis came out of a cabinet with a necked tube and the red cutoff pot was damaged. The pot was already replaced, so I am going to check the red transistor and input pins on the neckboard.

 

[SpoonyBard]

Revisited this chassis again tonight. Powered on and saw retrace lines then the picture went entirely white regardless of adjustments.

Set everything to 12 o clock, adjusted the flyback with no change. Shut down and reapplied power, then received an image that faded to nothing but very dim, red colors.

Adjusting the focus knob still provides a picture for a brief time. Then it fades to this dim red image again. Left the monitor running for an hour and there was no change.

Bumping for any potential insight. Could this be some kind of shutdown related to convergence? A b+ issue? As this chassis has no adjustable b+, am I fighting a losing battle?

 

[SpoonyBard]

Shotgunned this one. I noticed that the retainer for the convergence rings was not straight, so I adjusted that. Then I reflowed every pad on the neckboard.

Currently the monitor has been running for 20 minutes with no issues. The convergence is way off. But it's a start at least.

 

[SpoonyBard]

Left the monitor running for over an hour and noticed that the picture was dark, but still visible. A drastic improvement over its previous setting.

Adjusting the focus setting on the flyback still causes the picture to get significantly brighter. However it still fades over several seconds.

Adjusting the screen setting will impact brightness, but I can not get retrace lines by adjusting it here. Adjusting focus will get the picture bright enough to produce retrace lines.