If I trace the 12V STB properly, I arrive on 2651MTC-ADJ regulator circled in red in the picture.
I tested all the capacitors around and i disconnected the diodes to isolate the input and output of the regulator.
after measurements between the input (Vin) and output (SW) I feel that the Internal MOSFET is dead but this remains to be confirmed.
Hi richnormand.
at different power with old TOP200, I measured on a 12V STB a 18Vdc briefly.
the maximum for the LM2651 is 14V, I think he's burning at that time.
Just had a look in one of the PSU's i've got, and the 6 1ohm resistors you have are different to mine, cause one of them is a diode.
I'll have to have a look at the other psu later, just in case it's a difference in the versions.
Just poked the outputs with the scope to see what was happening, and here's the result.
Started with the mains turned off, mains on, then B1 to ground, and then mains off in 10 ish second chunks, and like i said, 3.3v and 5.2v are dead, and A1 starts up, then dies, what i found interesting was the 12v line going to where it is, then crashing to ~8v.
Ignore the little wobble on the 12v just as it went high, fat fingers and tiny wires don't work well .
3rd picture is the same test, but with a working psu.
So at least from that we know that the 12v dying isn't due to a fault, but something is stopping the psu causing 12v to drop like it does on the working psu.
Time for a cold drink and a think.
**edit**
Well i've checked the resistors, and they're 1ohm each, so time to try and find the 5 and 3v lines.
Found it!
It seems to be the UC3843AN on the add on board, or something else on it (op amps), cause when i swapped them around, the working psu dies the same way the broken psu did.
So, off to RS to order a pack of them, just in case .
Wonder what caused it to die.
Going to compare the signals going in and out of both psu's so hopeful everyone else can just shove a probe on pin x to determine if that's the board that's died, seeing as it's buried deep inside the psu.
https://www.fairchildsemi.com/datasheets/uc/uc3843.pdf
There's the comparison of the traces of both board.
Found it!
It seems to be the UC3843AN on the add on board, or something else on it (op amps), cause when i swapped them around, the working psu dies the same way the broken psu did.
So, off to RS to order a pack of them, just in case .
Wonder what caused it to die.
Going to compare the signals going in and out of both psu's so hopeful everyone else can just shove a probe on pin x to determine if that's the board that's died, seeing as it's buried deep inside the psu.
https://www.fairchildsemi.com/datasheets/uc/uc3843.pdf
There's the comparison of the traces of both board.
Nice to have a comparison between the good and bad unit! I'll be intriged to find out what RS wants for it.
Found it!
It seems to be the UC3843AN on the add on board, or something else on it (op amps), cause when i swapped them around, the working psu dies the same way the broken psu did.
So, off to RS to order a pack of them, just in case .
Wonder what caused it to die.
Going to compare the signals going in and out of both psu's so hopeful everyone else can just shove a probe on pin x to determine if that's the board that's died, seeing as it's buried deep inside the psu.
https://www.fairchildsemi.com/datasheets/uc/uc3843.pdf
There's the comparison of the traces of both board.
Nice to have a comparison between the good and bad unit! I'll be intriged to find out what RS wants for it.
I mean RS Components for the UC3843AN , £5 for 5.
Found it!
It seems to be the UC3843AN on the add on board, or something else on it (op amps), cause when i swapped them around, the working psu dies the same way the broken psu did.
So, off to RS to order a pack of them, just in case .
Wonder what caused it to die.
Going to compare the signals going in and out of both psu's so hopeful everyone else can just shove a probe on pin x to determine if that's the board that's died, seeing as it's buried deep inside the psu.
https://www.fairchildsemi.com/datasheets/uc/uc3843.pdf
There's the comparison of the traces of both board.
Well i replaced the UC3843AN, and that didn't do it, but 1 board works and the other doesn't, as before.
So, the other chips on that board are an LM393M, a CD4001BCM and a TLE2022c.
If it wasn't for the fact that swapping out this mini board made the psu work, i'd be looking further up the line. Hopefully it isn't one of the many transistors on that board.
Good evening.
small post to confirm my troubleshooting CMU200.
Testing the CPU directly connected to the CMU ( Without LCD, PCMCIA and keyboard ) > CMU works well. ( motherboard post boot BIP)
reassembly of the front panel and replaced on the CMU.
everything is Ok my CMU working again.
If it helps users CMU200 or CRTU, hoping to be useful.
Since you know which one is bad I would be tempted to put both beside each other, in the same orientation.
Use the DMM on the diode ohm scale and systematically probe each transistor and diode looking for a difference between the two. Reverse polarity if you don't find a difference and repeat.
Similarly on the input, output and Vcc of the opamps. Just finding a difference may be of help.
Finally do a board to board comparison of resistors and other components.
I realise these are still in circuit so its not really a test of the component at this stage but there "should" be a difference between the two boards somewhere lest the flaw is hidden deep in one of the ICs.