replacing uc3845b with uc3842an

[MXM]

hey, hello everybody... ive been trying to fix these damn pdp-124p PSUs and i havent been able to fix one...(got 6 broken, 1 works cause thats how i found it ).

the working one, contains from factory the pwm 3845. (ST)

ive been replacing 3845 with 3842 (Moto), but after so many failures i decided id take a look at nte cross refernce and see if the nte replace matched.... and surprise they didnt... i did not look further to see those nte replacement datasheets, but i have both 3842 (Moto) and 3845 (ST) datasheets and seems they have a flip flop thingy difference.... my question is: could this be the possible cause of why i just cant fix a single one?
i am concerned that nte cross ref returned different nte replacement part numbers for each (i was expecting, the same)

according to nte this is the replace for each
UC3842AN -> NTE7096
UC3845 -> NTE7099

please advise, i was given 3842 with the promise it was the same replacement.... if not, wel, that money to the trash but my main goal is to fix those damn PSUs... i dont mind going to buy 3845 and getting this time 3845 (i was given 3842 and being told they were a perfect replace for each other at all cases.... x2)

diode test
with em both not soldered, the reads i get putting the black lead (DVM) on the pin 5 (GND) differ one from each other on pin 5-6 (only)

3845 returns open circuit while 3842 returns certain value (around 2.2...)

I just wanna know if im going nuts or if they should properly work (compatible replacement for these PSUs) and my problem is not here....

Please help.

Thanks.

Peace.

[MXM]

Re: replacing uc3845b with uc3842an

i didnt find the EDIT on my first post, so... heres more info

i grabbed another 3845 from one of my other broken (maybe this is why is broken) PSUs, it turned out weird, cause, i do not know for sure if it (this second 3845) works, but it throws me the same reads as the 3842 that i have bought... so one of my assumptions is that maybe, this 3845 is also broken and that is why i cant replace 3845 with 3842,... i really find weird that all the measurements ive taken with it are equal with the 3842 BUT, it differs from the working 3845 i got...

A=working 3845 taken from a working PSU
B=brand new 3842 just bought
C=unknown state 3845 taken from a broken PSU

B and C throws me the same values, but A differs from C.....

any ideas are welcome and appreciatted.

peace.

[Wizard]

Re: replacing uc3845b with uc3842an

Even the suffix is significent and rarely maker.

Pull up the data sheets for all three. Even one item different result in a failure.

Pays to use exact same part number example:

UC3845 replaced by another maker of KA3845 or UC3845AN etc. It is all in the datasheet you have to search for.

Sometimes different digits is compatible but there are a reason, again the datasheet will tell the truth.

Cheers, Wizard