Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old March 16th 21, 11:25 PM posted to sci.electronics.repair
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Default RCA main board

On Monday, March 15, 2021 at 7:07:02 PM UTC-4, wrote:
On Monday, March 15, 2021 at 2:13:19 PM UTC-4, three_jeeps wrote:
On Sunday, March 14, 2021 at 2:51:41 PM UTC-4, wrote:
On Sunday, March 14, 2021 at 1:41:01 PM UTC-4, Stu jaxon wrote:
On Tuesday, December 8, 2020 at 7:50:49 AM UTC-5, wrote:
On Monday, December 7, 2020 at 9:03:09 PM UTC-5, wrote:
Hi Group, need help choosing a main board for an RCA TV model ... led32c45rq.. main board # fre01m3393lna35-a2.. i want to know if this board ..42RE01M3393LNA35-A2 Main Board for LED42C45RQ will work in replace of the one mentioned ???
The only way is to try it. There are two potential problems of high probability: the keyboard switches may not work as assigned, and you may have no picture, a badly pixelated picture, or an upside down picture because these boards don't drive the same screen. If the board is close enough, swapping the eeprom from the original board will usually fix the picture issues and likely the keyboard issues, but that's assuming the original eeprom is good. Since the eeprom is the most likely cause of any non-lightning failures of these boards, you may be moving a bad eeprom into a good board.

I've done that type of swap when I had a board in stock as it only takes a few minutes to try it, but wouldn't order a board for the attempt..

Did you confirm the power supply is OK? Getting standby 5V is not enough. You can jump the stby pin to the ps on pin and see if the 12V comes up. If it doesn't, the power supply is bad. If it does, it's the main.
I'm reading a short across both sides of the fuse 3a/125v to ground, on the tcon board, there's short somewhere.???
With the LVDS cable disconnected, you should not be getting any low resistance to the ground screws of the TCON. If so, there's a short. The most common reason for a dead short on a TCON are one of the multi layer chip capacitors (they're surface mounted and have no markings). While any dead short is easy to find with an ohm meter, these caps are usually found in groups of two to ten or more all paralleled, so one shorted cap makes them all look bad. Other than a Huntron, the easiest way to find this is to feed a limited current (2 amps tops) into the short with a variable supply and spray the board with freeze spray until the board frosts over. The first cap to thaw is the shorted one.

Extremely clever, and useful. Will have to file this trick away.
I usually do hunting by keeping the board powered up for a bit then spray targeted components.
Thanks
J

That works if the supply maintains the struggle of feeding the short, but most of these more recent circuits (like these TCONs) are fed by buck converters who shutdown when the programmed current value is reached, so the offending load part never gets hot. When using the forced current trick, one must remember to limit the voltage, as sometimes the shorted part may suddenly open under the strain and an over-voltage will then damage something else.



I have a variable ps, and medical freeze spray, but i never injected a voltage/current into a circuit. could use some tips/pointers.??

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Old March 17th 21, 04:54 PM posted to sci.electronics.repair
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Default RCA main board

On Tuesday, March 16, 2021 at 7:25:57 PM UTC-4, Stu jaxon wrote:

I'm reading a short across both sides of the fuse 3a/125v to ground, on the tcon board, there's short somewhere.???
With the LVDS cable disconnected, you should not be getting any low resistance to the ground screws of the TCON. If so, there's a short. The most common reason for a dead short on a TCON are one of the multi layer chip capacitors (they're surface mounted and have no markings). While any dead short is easy to find with an ohm meter, these caps are usually found in groups of two to ten or more all paralleled, so one shorted cap makes them all look bad. Other than a Huntron, the easiest way to find this is to feed a limited current (2 amps tops) into the short with a variable supply and spray the board with freeze spray until the board frosts over. The first cap to thaw is the shorted one.
Extremely clever, and useful. Will have to file this trick away.
I usually do hunting by keeping the board powered up for a bit then spray targeted components.
Thanks
J

That works if the supply maintains the struggle of feeding the short, but most of these more recent circuits (like these TCONs) are fed by buck converters who shutdown when the programmed current value is reached, so the offending load part never gets hot. When using the forced current trick, one must remember to limit the voltage, as sometimes the shorted part may suddenly open under the strain and an over-voltage will then damage something else.

I have a variable ps, and medical freeze spray, but i never injected a voltage/current into a circuit. could use some tips/pointers.??

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Old March 17th 21, 04:58 PM posted to sci.electronics.repair
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First recorded activity by DIYBanter: Aug 2020
Posts: 96
Default RCA main board

On Tuesday, March 16, 2021 at 7:25:57 PM UTC-4, Stu jaxon wrote:

I'm reading a short across both sides of the fuse 3a/125v to ground, on the tcon board, there's short somewhere.???
With the LVDS cable disconnected, you should not be getting any low resistance to the ground screws of the TCON. If so, there's a short. The most common reason for a dead short on a TCON are one of the multi layer chip capacitors (they're surface mounted and have no markings). While any dead short is easy to find with an ohm meter, these caps are usually found in groups of two to ten or more all paralleled, so one shorted cap makes them all look bad. Other than a Huntron, the easiest way to find this is to feed a limited current (2 amps tops) into the short with a variable supply and spray the board with freeze spray until the board frosts over. The first cap to thaw is the shorted one.
Extremely clever, and useful. Will have to file this trick away.
I usually do hunting by keeping the board powered up for a bit then spray targeted components.
Thanks
J

That works if the supply maintains the struggle of feeding the short, but most of these more recent circuits (like these TCONs) are fed by buck converters who shutdown when the programmed current value is reached, so the offending load part never gets hot. When using the forced current trick, one must remember to limit the voltage, as sometimes the shorted part may suddenly open under the strain and an over-voltage will then damage something else.

I have a variable ps, and medical freeze spray, but i never injected a voltage/current into a circuit. could use some tips/pointers.??


Simply feed 2 amps (but no more) on either side of the fuse with respect to ground (the screw lands are fine). Since the input to the TCON is 12V, make sure your supply does't go over 10V or so. With a dead short, you should be reading mostly current and almost no voltage. Spray the whole board with freeze spray so it frosts over. Watch what thaws first. Could be one of the brown chip caps or even one of the chips.


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