K7000 Medium Res - Tearing my hair out.

[EagleTG]

Ok, this chassis is a pain in the ass. Everyone knows that these run hot. This one is no different.

I've worked on this monitor so many times, and for so long now, I don't remember all of the details.

I've done a cap kit, repaired various other failures (bad power resistor, bad VR, tons and tons of trace issues/broken solder). After each piece I replaced, marked improvement was noted. The monitor now works, but only for a brief period of time (until R101 desolders itself).

I've rebuilt the traces around R101, thoroughly verified that it's soldered in securely and correctly, run a new trace with a solid wire from the resistor to the component it runs to (don't remember off of the top of my head). Yet, it will still desolder itself.

The resistor is a 6.8K 3 Watt, it tests in-spec. I'm assuming it's bad, generating too much heat, and removing itself from circuit. Can one of the monitor gurus out there confirm my suspicion or suggest alternative ideas? I've read a few comments and posts that seem to indicate that R101 doesn't typically go bad, I know that doesn't necessarily mean this one ISN'T bad.

This monitor is the bane of my existence. Projects come and go, monitors die and are fixed by my hand, eons and eternities pass, yet this FREAKING MONITOR STILL DOESN'T WORK RIGHT!! So I've got nothing else to do except post here asking for confirmation while I wait for yet ANOTHER part to come in (the resistor of which I speak).

Thanks everyone.

 

[KevinMullins]

Measure your B+ on both sides of R301. (the big white ceramic resistor mounted to the side)
Disconnect and Ohm R301 while your at it to see if it is in spec. (220Ohm)

 

[Ohmerone]

Ohm C23 cap 47/25v should be shorted.
another suspect would be Ic2 LA7823
@Pin 16,if it is shorted you won't get any Horizontal drive
and it will over heat R101.
If the B+ is way to high,these parts may fail again.
what is the B+

 

[cadillacman]

on the std res versions ive also seen those resistors change to a lower resistance due to running so hot, that makes them go lower, that makes them run hotter, that makes them go lower.. etc you get the idea.


Wether it tests ok with a meter or not, a new resistor is only a couple of bucks and at this point it might be a good idea just to replace it anyways.

 

[EagleTG]

Thanks Gents, I will check this stuff out tonight. I don't have the resistor yet, but will yank the old one and re-test. I might also solder it back in just to get another B+ reading.

The B+ was well within "spec" after I got the picture back the first time. Everything else is rock-solid with the monitor now, except for the resistor issue mentioned above.

I'm probably 85% sure the resistor will cure the issue. I just have to stop adding stuff to my parts order and actually submit the order. It's a fine balance. This resistor is a bit of a pain, as the usual folks I order from don't have it.