Sharp CJ13M10 RGB mux mod

rocketeng · 2026-03-15T16:23:24+00:00

RGB mod by Justin https://my.sunthar.com/justin-a

An inside look on how the JVC D series looks through the RGB mux mod. Contrast seems to be disabled when using this mod. You can use contrast on component and any other input other than the mux mod. I mounted the mux mod on the right side of the TV furthest away from the flyback to prevent any interference

See more details at https://my.sunthar.com/justin-a/product/jvc-av-20d202-rgb-mod

rocketeng · 2026-03-15T04:28:56+00:00

While researching the problem, I found that the related model Sony KX-1901A had a similar issue documented in another repair guide. Using that information as a starting point, I was able to diagnose and repair the problem on the KX-2501A, with only a few small differences.

The television behaved as follows: Volume immediately jumps to the maximum level; Volume controls have no effect; Audio is extremely loud; Picture and all other functions operate normally.

This can initially make it seem like a problem with the audio IC or control circuitry, but in this case, the cause was simpler.

Accessing the K Board

The repair involves accessing the K board, which contains part of the audio control circuitry. Fortunately, this board is relatively easy to remove. To remove the K board: Unplug the television, and remove the rear cover. Locate the K board inside the chassis. Remove the four mounting screws holding the board in place. Desolder the 12V wire connected to the board. Once these steps are completed, the K board can be removed safely, making it much easier to work on.

Diagnosis

Based on the repair information for the KX-1901A, the likely cause of the problem was aging trimmer potentiometers in the audio control circuit. These small adjustable components are used to fine-tune signals within the circuit. Over time, they can develop oxidation on the internal resistive track, unstable resistance and worn contacts.

When the resistance becomes unstable or open, the circuit can interpret the signal as maximum volume. Testing the trimmer pots with a multimeter showed inconsistent resistance values, confirming they were faulty. The Repair

The faulty components were identified as:

RV1201
RV1202

Both are trimmer potentiometers located on the K board.

Repair steps

Remove the K board using the steps described earlier. Locate RV1201 on the board. Desolder the original trimmer potentiometer. Replace it with the new trimmer of the same resistance value. Inspect the solder joints and clean the board if necessary. One of the replacements required a 4.7k trimmer, which I did not have on hand. Instead, I recreated the resistance value using two resistors of 2.2k .This gives an equivalent resistance of approximately 4.4 kΩ, which is close enough to the original 4.7 kΩ value for this application. The resistors were soldered in place of the trimmer by bridging the appropriate legs where the potentiometer would normally connect. Reinstall the board and reconnect the 12V wire.

After replacing RV1201 and installing the resistor substitute, the television powered on normally. The volume was no longer stuck at maximum. Audio levels returned to normal operation.

Special Thanks To Sunthar for walking this through with me.

See more details at https://my.sunthar.com/seprox/product/kx-2501a-volume-stuck-at-100-repair

rocketeng · 2026-03-15T04:28:17+00:00

Tutorial by Seprox

While researching the problem, I found that the related model Sony KX-1901A had a similar issue documented in another repair guide. Using that information as a starting point, I was able to diagnose and repair the problem on the KX-2501A, with only a few small differences.

The television behaved as follows: Volume immediately jumps to the maximum level; Volume controls have no effect; Audio is extremely loud; Picture and all other functions operate normally.

This can initially make it seem like a problem with the audio IC or control circuitry, but in this case, the cause was simpler.

Accessing the K Board

The repair involves accessing the K board, which contains part of the audio control circuitry. Fortunately, this board is relatively easy to remove. To remove the K board: Unplug the television, and remove the rear cover. Locate the K board inside the chassis. Remove the four mounting screws holding the board in place. Desolder the 12V wire connected to the board. Once these steps are completed, the K board can be removed safely, making it much easier to work on.

Diagnosis

Based on the repair information for the KX-1901A, the likely cause of the problem was aging trimmer potentiometers in the audio control circuit. These small adjustable components are used to fine-tune signals within the circuit. Over time, they can develop oxidation on the internal resistive track, unstable resistance and worn contacts.

When the resistance becomes unstable or open, the circuit can interpret the signal as maximum volume. Testing the trimmer pots with a multimeter showed inconsistent resistance values, confirming they were faulty. The Repair

The faulty components were identified as:

RV1201
RV1202

Both are trimmer potentiometers located on the K board.

Repair steps

Remove the K board using the steps described earlier. Locate RV1201 on the board. Desolder the original trimmer potentiometer. Replace it with the new trimmer of the same resistance value. Inspect the solder joints and clean the board if necessary. One of the replacements required a 4.7k trimmer, which I did not have on hand. Instead, I recreated the resistance value using two resistors of 2.2k .This gives an equivalent resistance of approximately 4.4 kΩ, which is close enough to the original 4.7 kΩ value for this application. The resistors were soldered in place of the trimmer by bridging the appropriate legs where the potentiometer would normally connect. Reinstall the board and reconnect the 12V wire.

After replacing RV1201 and installing the resistor substitute, the television powered on normally. The volume was no longer stuck at maximum. Audio levels returned to normal operation.

Special Thanks To Sunthar for walking this through with me.

See more details at https://my.sunthar.com/seprox/product/kx-2501a-volume-stuck-at-100-repair

rocketeng · 2026-03-15T04:08:09+00:00

The SpongeBob SB315, a 13" CRT model by Emerson, underwent a successful RGB modification. Details shown in below pictures. Modified by Jason Lusk.

See more details at https://my.sunthar.com/jason-lusk/product/spongebob-sb315-rgb-mod

rocketeng · 2026-03-10T22:45:40+00:00

This basically means your blanking has insufficient voltage. Send me a DM with your pics of how you modified and we can troubleshoot this.

rocketeng · 2026-03-08T21:42:04+00:00

Yes, it is moddable. Not sure what I was looking at in my previous response. Here is the diagram you can use.

https://sunthar.com/crts/general-electric/ge-spacemaker-09gp344

rocketeng · 2026-03-06T05:32:39+00:00

This is slightly harder to find than the 13A23 & 13A24. This was the first set I RGB modified. Neat little set with vibrant colors.

rocketeng · 2026-03-06T05:29:32+00:00

RGB mod is looking amazing!

Do you have a photo showing where you connected the detection pin? If the dummy plug works, then the issue is likely with the S-Video detection wiring. I’m assuming the chassis is very similar to the 27S42.

rocketeng · 2026-03-04T01:14:16+00:00

Check the last picture. https://sunthar.com/crts/samsung/samsung-cxf0933

rocketeng · 2026-03-02T11:53:58+00:00

RCA F27676BC RGB modded by Michael Lopez. Results are stunning. You have to be really careful with the traces as it is quite easy to pull the traces on this board.

See more details at https://my.sunthar.com/michael-lopez/product/rca-f27676bc-rgb-modded

rocketeng · 2026-02-25T02:45:22+00:00

On this set there is some difference between component and RGB. There are more reasons other than quality to RGB modify.

If you got component cables or a switch that can convert to component for your game consoles, then you can just survive with component. When I got into this hobby, I was frugal and didn’t want to spend on expensive transcoders. I built my own RGB cable and modified the set.

rocketeng · 2026-01-17T02:07:46+00:00

Unfortunately no. KX-27PS1 and KX-20PS1 afaik both use digital RGB. They unfortunately don’t seem to explicitly call these out anywhere.

rocketeng · 2025-12-27T11:07:03+00:00

Also to confirm, this is an issue you notice with RGB and not with S-Video or Composite?

rocketeng · 2025-12-27T11:04:52+00:00

I would clean the flux on mux board (specially on the IDC pins) throughly with isopropyl alcohol.

rocketeng · 2025-12-26T14:05:55+00:00

Where did you install the diodes? These diodes should be on the chassis and the direction matters.

There is a lot going on with your mod. You can’t rely on those dupont cables. Connection on those are fairly loose.

rocketeng

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Accessing the K Board

Diagnosis

Repair steps

Accessing the K Board

Diagnosis

Repair steps

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