Tektronix 7704A power supply question

Manuals (free) for 7704 & 7704A can are here:

These guys can answer your TEK question:

Ed

Hmm..the schematic i have shows only 3 neons, one between the 115V and the 230V switch terminls, one in oscillator configurationacross the output of the FWB, and the third from the 115V switch terminal to some ?reference? line. In certain applications, neon bulbs were purposly burned in (for looong periods), turning them black inside, in order to gain voltage stability. I understand the technique is both an art and a science.

I could make a copy of that one sheet (includes power supply inverter board that i talked about) if you want; the manual i have is a copy.

Robert Baer wrote in news:vpOdnXrTtKEdLz7UnZ2dnUVZ snipped-for-privacy@posted.localnet:

older 7704A's used to have a neon-based start circuit instead of the 32V diac. the ticking is the supply trying to start.

That now wants a user name and password :-(

Anyhow, I've seen the manuals. Problem is, there is only a manual with schematics for the 7704 which is hugely different from the 7704A. Tek made a lot of customs chips for that, of course now all pretty much unobtanium.

Thanks, I'll try that.

That's what I was afraid they did. I've seen them used as references as well, a quite horrid method because when it fails you are up the creek. If I had the schematic I could try to replace it with something more durable. Did you find the 7704A schematic online somewhere? BAMA and Bitsavers didn't have it. Only the 7704 non-A and that's way different, mostly discrete while the 7704A has those new-fangled Tek custom chips :-(

Thing is, after I fixed it the supply starts every single time. After it starts the ticking and neon flashing continues.

One of the reasons I keep on using this scope is the incredibly sharp CRT display. Even the venerable 2465 can't rival that. Plus it has that ghostly blue glow in the dark after I shut down the lab, kind of cool. Some day I am going to get me a 7L13 or so for it, just for kicks.

Yes, Robert, that would be nice. But only if you have a scanner and it's not much work:

jsc ieee

BAMA (the Boat anchor Manual source) prompts for a username/password if there are too many users on at a time. Unfortunately with BAMA, that is most of the time.

Here is the mirror for BAMA, which has the same manuals available, with a more robust data pipeline:

Thanks, Ed, I've bookmarked it. Unfortunately (for me) this site like the others only has the user manual for the 7704A. No schematics :-(

Hi Joerg,

the 485 (which is about the same date of engineering and the power supplys seems to have the same common hand..) has a little neon lamp in the power supply to warn that the "line storage capacitors" are charged.

From the 485 Manual:

"Because the discharge is slow, dangerous potentials will exist across capacitors C1822, C1823, and other connected components for several minutes after the power switch is turned off. The presence of voltage in the circuit is indicated by relaxation oscillator R1824, C1824 and DS1824. Neon Bulb DS1824 blinks until potential drops to approximately 100V"

Maybe the 7704A has the same technican-friendly feature...

Jorgen

Sounds odd that it has that symptom and still works. I used to repair a lot of switching P/S's and the ticking is a common symptom. 99% of the time they have bad caps. When testing and/or replacing caps in the switcher, be sure to test them for low ESR. This is a must. As far as the neon lamp, I've often seen them used for over voltage protection.

Tony

Thanks, Jorgen. If that's true for the 7704A as well then I could just blissfully ignore it. Nowadays such a warning wouldn't hold water in court anymore because it ain't bilingual :-)

Joerg, You can download the complete manual set for the 7704 and 7704A scopes from

Cheers!

But wouldn't it have been removed anyway to save the extra $0.25 in manufacturing parts? :-)

the

the

the

Thanks! Excellent! A3 are the schematics, all I need, very readable.

Robert, thanks for the offer but Dave pointed out where I could download the complete set of schematics:

Seems they didn't, maybe their lawyers insisted it should stay ;-)

Anyhow, Dave pointed me to a source for the schematics and it seems they did indeed place it there to indicate that there's juice on the caps. So if it quits I won't care because I always assume residual voltage on line side caps and other caps when working on stuff. As to why it causes a ticking noise, no idea. According to the architecture of what looks like a series resonant converter it shouldn't.

"DaveM" wrote in news:KZ-dnYGRzOqFrTnUnZ2dnUVZ snipped-for-privacy@giganews.com:

you do know there's a huge difference between the 7704 and 7704A?