common k7000 issues - common repairs

Ran into one with a lot of oxidized pads on the power resistors (R89/R101/D18) and figured I'd share my method for fixing them.

 
IDK if this is common, but it's new to me, so I thought I'd log it here. I had a 7000 with the normal re-work, inspection, caps, replace blown up flyback, new HOT, new VR (all tested bad). Power section working great.

Total vertical collapse. Do the normal things, replace IC3, 2. No help. Start looking at the obscure things like c51, etc, can't find any other issues.

The new IC3 was assumed to be good, but it's been a while since I had a legit failed one. The interesting part is I got lucky probing around and noticed that the heat sink for IC3 had continuity to pin2 of IC3, which is wrong.

Looking around I noticed that the heat sink itself does not have a direct connection to chassis ground; each pad that holds the sink to the PCB are floating. The heat sink is connected to chassis ground via Pin1, which is also connected to the backside of the IC, which sits against the metal heat sink. This is why there is no mica pad on IC3 (unlike IC1 & 4).

Robbed another IC3 from another chassis and it works perfectly. Again, maybe this isn't news to anyone else, but it was new to me.
 
IDK if this is common, but it's new to me, so I thought I'd log it here. I had a 7000 with the normal re-work, inspection, caps, replace blown up flyback, new HOT, new VR (all tested bad). Power section working great.

Total vertical collapse. Do the normal things, replace IC3, 2. No help. Start looking at the obscure things like c51, etc, can't find any other issues.

The new IC3 was assumed to be good, but it's been a while since I had a legit failed one. The interesting part is I got lucky probing around and noticed that the heat sink for IC3 had continuity to pin2 of IC3, which is wrong.

Looking around I noticed that the heat sink itself does not have a direct connection to chassis ground; each pad that holds the sink to the PCB are floating. The heat sink is connected to chassis ground via Pin1, which is also connected to the backside of the IC, which sits against the metal heat sink. This is why there is no mica pad on IC3 (unlike IC1 & 4).

Robbed another IC3 from another chassis and it works perfectly. Again, maybe this isn't news to anyone else, but it was new to me.
Just fixed one a few moments ago that was in total vertical collapse. None of the normal causes. 26vdc reference present at the IC3. Found the C53 poly cap damaged/exploded on the top and dead shorted. H.Hold pot was broken and V.Pos pot was bad (just spins around 360). Replaced the two pots and the shorted C53. After some adjustments, it's back to fully working. Never seen C53 go bad before.
 

Attachments

  • 5.JPG
    5.JPG
    393.1 KB · Views: 11
  • 6.JPG
    6.JPG
    452.1 KB · Views: 11
  • 7.JPG
    7.JPG
    307.6 KB · Views: 11
Monitor- K7000 19" P447

Symptoms- Blown fuse

Tested and replaced R103, HOT, and VR. Monitor kept blowing fuse, upon closer inspection, found D103 pad was disconnected, removed and bridged the leg. Monitor kept blowing fuse, tested all components and found no other issues. Looking closely, I could see just a smidge of a brown hard substance at the top of the fb, had thought it was an epoxy of some sort. Replaced flyback, bam, monitor up and running. I was apprehensive about the flyback as it was from a well known supplier, but no telling how old or how many hours are on it.
 
Got a strange one. Come across a 25' k7000 with a blown fuse and HOT. Removed HOT and tested pads for a short but nothing. Replaced HOT with new mica and fuse. It powered on and got good HV but B+ was around 125v then I can hear the shutdown circuit kick on and then voltage dropped to 120. I quickly turned it off. Shutdown circuit never cut off the chassis. Thermistor was scolding hot. I tried it again a little longer same results but the HOT blew again. Checked the thermistor again, same results, super HOT. Performed the lightbulb test and got 125. Replaced VR but still got 125. Threw in a new FB and a new c36, but HOT blew again.
Replaced VR, mica, FB and c36.
Symptoms persist. Blows HOT's, and thermistor is super hot.
 
Got a strange one. Come across a 25' k7000 with a blown fuse and HOT. Removed HOT and tested pads for a short but nothing. Replaced HOT with new mica and fuse. It powered on and got good HV but B+ was around 125v then I can hear the shutdown circuit kick on and then voltage dropped to 120. I quickly turned it off. Shutdown circuit never cut off the chassis. Thermistor was scolding hot. I tried it again a little longer same results but the HOT blew again. Checked the thermistor again, same results, super HOT. Performed the lightbulb test and got 125. Replaced VR but still got 125. Threw in a new FB and a new c36, but HOT blew again.
Replaced VR, mica, FB and c36.
Symptoms persist. Blows HOT's, and thermistor is superheat.
Is it typical for the shutdown circuit kick in when it's undervoltage?
 
If this is a 25" it may be missing c69? This issue makes the HOT run super well, hot.

Mike did a video on this
 
19K7900...had full vertical collapse on initial start up. Gave it the normal treatment cap kit, reflow, tested the usual suspects (resistors, diodes, regulator). All checked good so I put it back together and tried it. No change.

Next I double checked everything and checked the yoke, pots and swap tested IC2, put it back together and...no change.

Pulled it AGAIN and noticed the solder on c40 had made a perfect straight line across the trace indicating a possible broken trace so I bridged the gap. Fired it up and now partial collapse. About 2-3 minutes and it was back to full collapse.

Lastly I went to the schematic and made a list of everything in the vertical size circuit starting at the flyback pin #4 to IC2 pin #9. Sixteen parts and voltages. Finally got to #11 (R77) in circuit read 30M was supposed to be 33K. Obviously tested open out of circuit. Replaced it, fired it up and Boing! Full deflection.
 
Last edited:
19K7900...had full vertical collapse on initial start up. Gave it the normal treatment cap kit, reflow, tested the usual suspects (resistors, diodes, regulator). All checked good so I put it back together and tried it. No change.

Next I double checked everything and checked the yoke, pots and swap tested IC2, put it back together and...no change.

Pulled it AGAIN and noticed the solder on c40 had made a perfect straight line across the trace indicating a possible broken trace so I bridged the gap. Fired it up and now partial collapse. About 2-3 minutes and it was back to full collapse.

Lastly I went to the schematic and made a list of everything in the vertical size circuit starting at the flyback pin #4 to IC2 pin #9. Sixteen parts and voltages. Finally got to #11 (R77) in circuit read 30M was supposed to be 33K. Obviously tested open out of circuit. Replaced it, fired it up and Boing! Full deflection.
Nice find!
 
Back
Top Bottom