<fingers crossed>
-Pat
HELP HELP HELP!!!! Before inserting the 7812C (U100) onto the A71 Board, I checked it and also a 7805C on my Fluke meter "Diode Test" for a comparison. Well, the one I pulled off the board was rather unlike either of the two fixed regs I had for comparison, and it didn't seem shorted either when out of the circuit.
Boy am I glad I didn't turn this thing on... As you stated - the <+> and <-> regs have different pinouts.
There are also different pinouts for the variable type regs, compared to the fixed ones! I guess I just assumed the U100 part was a 7812C...
First of all... This is why I
HATE House Numbered Parts ... You need the Service Manual to know what anything actually is, and finding that in a .pdf file often takes hours.
AS IT TURNS OUT, that the 7812CV I put on the A71 PS Board at part U100 should not be a
7812CV after all !!!
At this point I'm not sure what it should be I seemed to recall that the middle pin on a <+> reg goes directly to Ground. Yet the 3561A schematic in the SM shows a 1.07K resistor to ground on part U100.
There is also the same resistor present on the U001.
So I started saying... WHAT
I double checked the 3561A Service Manuals Vols 1 and 2, and found conflicting information.
According to the
Parts List, the SM says that part U100 should be: (1826-0527) is an LM337T. And part U1 should be: (1826-0393) which is an LM317T!
HOWEVER! On my 3561A, present on the A71 Board, U100 is clearly marked (1826-0393) which is an LM317T, and part U1 is (1826-0527) which is an LM337T!
Now, did some dumber than me tech replace and switch these two parts at some point in the last 33 years, Or -
Is the HP Service Manual WRONG? Again, now I have to pull that 7812 and insert the right part which - according to all that I hold truthful, probably should be: the LM317T (unless HP went out of their way to reverse these two parts, for no good reason). So Most Likely, the SM is WRONG and my A71 Board is RIGHT!
So Pat, its quite easy to see which part on A71 is U1, its not blocked by a big C102 as the U100 is on the heatsink.
So, can you please verify that on your A71 Board you have (1826-0527) for U1 (LM337T) in which case I need to find an LM317T, or put the original part back (but not sure I trust it, I would like to compare it with a few other 317T's first, in which case, if the readings don't match, I'll use a different 317T part).
Thanks,
-Steven