On 12/1/19 1:29 PM, John Robertson wrote:
On 2019/12/01 11:02 a.m., Fox's Mercantile wrote:
On 12/1/19 12:38 PM, John Robertson wrote:
On 2019/12/01 9:00 a.m., Cursitor Doom wrote:
Gentlemen,

On the HP audio spectrum analyser I'm now working on, I've found all
the
low voltage regs seem fine (sub 30V I mean) within a few hundredths
of a
volt to what they should be. The medium voltages are not so close to
what
those printed on the PCB state they should be, however. I've got points
on the board that are supposed to be 150V reading 170V and (less far
out)
an 80V rail reading 84V. 150 reading 170 seems to me to indicate a
regulator gone short, possibly. Anyway, question No.1 is: has anyone
encountered readings that were this far out from those stated but which
turned out to be nothing to worry about in the end?
Question No.2 is: should I investigate the 80V -- 84V anomaly?




On the HP schematic notes what was the VOM loading factor? Back in
the day 100K Ohms/volt (analog meter) was not unusual so your
"over-voltages" may simply be the result of under-loading the circuit
with your modern DVM.

John :-#)#

If aÂ* power supply voltage can be loaded down by a 10-20 Meg resistance,
there's something seriously wrong with the supply.



Sorry, I believe I was thinking of 1000 Ohms/V meter when I was speaking
of loading.

https://www.allaboutcircuits.com/tex...sured-circuit/


Spoiled by DMMs one gets rusty on one's assumptions.

Thanks!

John :-#)#


Even so, a 100K load shouldn't load down a power supply.


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com