My Ongoing Monitor Repair Logs

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Sharp Image/Kortek KTM-F

Symptom: Image pulsing. Bright edge on bright to dark transitions

Flyback had quite literally exploded on this chassis and seemingly took out the ABL circuit, found C115 and Q101 bad. Found R314 missing entirely on neck board. Real fix though was that someone for some reason bridged the RGB input pins to the pin next to it sequentially. So R video was bridged to G data input, G video was bridged to B data input, etc. Looked like a factory bodge? Undid it and the image looked perfect.

EDIT: Part 2: High B+ 133v

The same chassis had B+ sitting at around 133v, when it should be 123v measured at D605. A bunch of stuff was getting quite hot on the chassis due to this and several spots were discolored.

The cause of this is stupid. See this bodge on T601? On my good chassis, this bodge is here. The reason for this bodge is because the pin underneath the pad is missing, and 123v B+ voltage actually comes off the pin with no pad. The factory clipped the pin off the transformer and just bodged the pad to the correct pin. On the bad chassis, the pin was intact and soldered hence the 133v B+, so I did the same thing the factory did and removed the transformer, clipped the pin, then reinstalled the transformer and bodged a jumper on. Wowee, 123v.

 

[trashedcabs]

WG K7500

Symptom: Blowing HOT quickly, horizontal collapse (vertical line)

C722 poly cap shorted. Replaced to fix.

 

[trashedcabs]

I fell into a pile of multiple K7400/K7500 chassis I needed to repair. All 6 of these had dead HOTs, and I replaced with 2SC5612 which is the highest rated and cheapest HOT I've been able to find as an authentic part. The following caps were found bad or out of spec on every single one:

C615
C716 (should really be upgraded to a high temp cap)
C731
C800
C805
C812

The big 10uf 50v BP cap should NOT be replaced unless it's confirmed bad. This is a special high-ripple, high-frequency cap used for horizontal deflection and needs to be replaced with one of the same spec. The only one I can find for sale anymore is the Xicon BPHR-50v10-RC which is EOL old stock. The cap included with the APAR kit if you buy it is not correct and will fail quickly if installed, but generally I would advise sourcing your own parts anyway to save money.

Symptom: VERY high B+ (210vdc with lightbulb load!!!!)

U101 bad, replaced and it stabilized to the higher end of the adjustment range. B+ pot also oxidized despite being factory glued, broke it loose and deoxited the pot to fix.

Symptom: Rolling distorted image

Q700 bad. Replaced and all problems were fixed. Two monitors had this same issue.

Symptom: Dead. No vsync, vhold adjust did nothing

Found output diode D118 shorted, board powered up after this with good B+. BTW, you can use 1N4937 to replace the RU2 diodes used in a lot of monitors.

No V sync was due to wrong remote board. 4/6 chassis had U5000 P718 remote boards which needed to be modified to work with the K7400/K7500. You need to replace a couple pots, replace both resistors, cut two traces on the vhold pot and add two jumper wires.

Symptom: Dead

This was corroded and missing a lot of components. Cleaned it and put all components back and it was totally dead, no output at all from the PSU mosfet. Checked a lot of components in the power supply, took a lot of measurements and didn't find anything. Followed the advice of zenomorp and reflowed the entire PSU section and it fired right up.

 

[nem]

The big 10uf 50v BP cap should NOT be replaced unless it's confirmed bad. This is a special high-ripple, high-frequency cap used for horizontal deflection and needs to be replaced with one of the same spec. The only one I can find for sale anymore is the Xicon BPHR-50v10-RC which is EOL old stock. The cap included with the APAR kit if you buy it is not correct and will fail quickly if installed, but generally I would advise sourcing your own parts anyway to save money.

I was wondering about this sometime back. Would a film cap be a bad idea?

 

[trashedcabs]

I was wondering about this sometime back. Would a film cap be a bad idea?

I'm not an electrical engineer, but from my understanding a film cap should be even better at handling high frequency AC ripple.

 

[trashedcabs]

WG K7500

Symptom: Width control only half works

Someone followed a cap list but did not put C729 in the correct spot. On the K7500, the 10uf 50v BP high ripple cap that's normally in position C729 was moved to J5 above the yellow wire. Moved it to the correct spot to fix and replaced with a proper high ripple cap.

Also, this chassis came with a K7400 remote board, which has a few of the wrong pots installed. Really wish WG actually labeled these properly... they always seem to be mismatched.

 

[trashedcabs]

Neotec NT-2702

Symptom: No Sync

Deflection IC LA7851 bad, R407 found missing solder, seemingly a factory defect? No evidence of rework. Replaced and reflowed to fix.

 

[trashedcabs]

Kortek KT-3414DF

Symptom: Dead

Found HV drive mosfet Q603 and HOT both shorted. Removed both and checked for power out of the PSU but nothing... Swapped IC103 for a known good one and still nothing. I can see power coming from the drain of IC103 so clearly regulation is working, but for some reason nothing is making it out of the transformer. Reflowed T101 and got good power, installed new HV driver and HOT to complete fix. Nice easy one.


Nanao MS-2932

Symptom: No blue

Previous owner cracked the neckboard in half. Patched it up and no blue. Found R326 and ZD321 bad. Replaced to fix.


Nanao MS-2931

Symptom: No horizontal sweep (shutdown after 3 seconds)

Vertical sweep is good. I can see the H drive pulse out of the MCU and it stays active until shutdown, however going to T501 I can see the pulse for a few cycles before it goes away and stays high. Looking at pin 18 of the uPC1883 I see no H out pulse only a 60vdc solid voltage. Replaced with one from a parts chassis and it now powers up, but the sync is messed up. Replaced with a different uPC1883 from my junk bin and the sync issue was fixed.

Image was very red. Color signals coming out of the video amp to the neck board look good so it must be a neck board fault. Q303 was shorted, replaced to fix..

BTW, the infamous leaky coil L512 measures 4uH. Didn't see this info anywhere online.

 

[trashedcabs]

Sharp Image (Kortek) SI-727-DS

Symptom: Bad horizontal linearity but only when set to medium res

Spent way too long chasing this one. Ended up being either C417 or C418 failing under load despite testing good even when tested at 100khz using a DE-5000. I knew it had to be a poly cap so when I started shotgun replacing them, the problem went away.

The 134-DS schematic is very close to the 727, so use that when working on this monitor.

 

[trashedcabs]

A couple little repairs today. Trying to clear out the piles...

WG K7500

Symptom: Odd contrast behavior (colors clip/go at different rates as contrast pot is turned)

Neck board C512 ceramic found out of spec. Replaced to fix.

Sanwa 29E31S

Symptom: No width/pincushion adjustment

Flyback tested good in another chassis. Checked operation of the opamp and width control section and it seemed ok... Checked components around the H size output and after reflowing the area around Q413 the problem was fixed. People usually say replacing the flyback fixes this symptom but I'm sort of wondering how many of these chassis just need a reflow. They are junk chassis anyway imo.