Voltages too far out of spec?

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

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

of loading.

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

Thanks!

John :-#)#

On Sunday, December 1, 2019 at 12:00:21 PM UTC-5, Cursitor Doom wrote: The medium voltages are not so close to what

Over the years, I've seen voltages printed on PCs that were incorrect for t he version of board as loaded. IOW, manufacturers will often make running changes to a product design and revise parts loaded on the board and even u se a different transformer to feed it. Since they have may have boards alr eady screened, they're not going to scrap them out.

If HP has archived schematics, they may have a revised schematic that more closely or even exactly matches the voltages you're encountering.

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

On some of the old vacuum tube circuits I have seen schematics with several voltages at test points and a note as to a 20,000 ohm/volt or a VTVM is being used for the test.

Probably won't see much of that any more as with the solid state most resistances are low enough an analog meter will not load it enough and most are using digital meters to do the testing.

Those were almost always grid voltages. Those DID require a high resistance volt meter to not load them down. The other voltages in the set, plate, screen filamant were not that critical about loading.

istance,

I do recall schematics of old (mostly tube equipment) warning people that the readings were done with a specific Ohms/Volt meter and that readings would vary accordingly.

Mostly it is something to keep in the back of your mind when reading schematics and voltage test points...

Nice chatting with you!

John :-#)#

istance,

I dealt with troubleshooting and repairing a lot of consumer tube TV, stere os, and radios during the 60's and 70's. (Still have a collection of servic e manuals filling 4 large bookcases from my fathers shop). One of the most cited volt meters in the service manuals and schematics in that era was th e B&K 177 VTVM. On occasion, I would see a Sencore or Simpson 260 multimet er. As consumer electronics moved to all solid state (80s), I saw a B&K 3-1 /2 digit DMM specified (cant remember the model). At some point we went wi th HP gear. I think they speced equipment that was what the TV technicians were buying, as lab bench gear was quite a bit more expensive and did not require the l ab quality accuracy & repeatability numbers.

Occasionally I would run across a voltage tolerance spec on a schematic or SM, something like 5%, but dont recall exactly... J

Hewlett Packard isn't consumer grade. If they say 80v on a power supply, they mean 80v.

Yes, I would have agree, His readings indicate power supply regulation issues not VOM errors.

My mistake for going off on this tangent!

Sorry about that wild goose chase,

John :-#(#

I know that about HP. Been specing lab equipment for my uses in our/my labs for 35+ years. Apologies if it came across that way