hp 54503a scope psu recap

[m3vuv]

Hi all,i have just recapped my scope psu,the service manual states to adjust the 5.2v supplies,if i remember it should be done using a 2 ohm load resistor on the 5.2v rail,i didnt do that with mine,i just reconnected the psu as is,at the time the 2x 1 ohm 25 watt resistors were on order,they have now arrived,although the scope seems to be working fine and calibrated ok and passes all self tests,the question is,how critical is the 5.2v rail setting,and should i go and check/adjust it as the scope seems fine,also what outputs should i see at the rear bnc calibrator outputs,thanks in advance,m3vuv

[Wallace Gasiewicz]

Sounds like everything is fine. The 5 V on many HP units is used to power boards with TTL circuits. I have seen PS in HP units that have over power protection, so that the PS shuts down if there is a fault in one of the boards (usually a failed filter cap). TTL voltages are not horribly critical. However the voltage may be used to trigger an overload.
Perhaps the use of the low ohm load on the 5 V supply enables you to see if the PS does not shut off with a proper load, besides adjusting the volts,
I did not read the schematic and am just offering an opinion.
If this is the case that there is an over power circuit, it is not triggering and everything is fine.
I would think the outputs are probably TTL voltages so about 5 volts.

[m3vuv]

cheers for that,my only remaing issue is it seems the calibrator pigtails are crossed over ie the socket fron the r/h side of the mainboard connects too the l/h rear panel bnc,not sure tho as im not the first person inside this thing,have asked on io groups hp site but no answers,its like they are inverted!,also to do the cals had to invert the bnc cable,ie stuff it in the ac bnc rear bnc and not the dc one.

[SoundTech-LG]

No crossing over for the calibration coax. Each cable goes out straight from the board to the back panel.

[m3vuv]

that makes sense as it wont self calibrate unless i invert the cables.looks like someone has been in this before and swapped the pigtails.