[time-nuts] Re: HP 5065A, no 2nd harmonic.

[Henk Peek]

Jared,

 I think  an -20 V rail short to ground has first blowup A15Q10.
Then the -20V converter was light loaded and the output DC voltage goes up and blows also the zeners.
The most easy way to protect and repair: replace A15Q10 with a LM337 with 2 resistors to adjust the output to -20V.
Remove the blown zeners and diode and mount the 2 resistors on the removed zener positions.

Regards, Henk

On Thursday, December 02, 2021 15:15 CET, Jared Cabot via time-nuts <time-nuts at lists.febo.com> wrote: 
 
> So it looks like I lost the -20V rail. Seems that A15Q10 (2N4234), A10CR9A (9V Zener), and A15CR9B (11V Zener) are all dead for some reason.
> Q10 is easy enought o find, but the zeners are a little more tricky, they are specified as part number 1902-0247, a 20V, 1%, 0.4W +0.005%TC zener (20V made up of the 9v + 11V).
> I can find a 5% 9V (1N936A), but the 11V is harder to find.
> 
> Maybe I should look into redesigning this board entirely, the transformer on mine is rather noisy anyway.....
> 
> Schematics attached for reference.
> 
> 
> 
> Jared
> 
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> 
> On Thursday, December 2nd, 2021 at 21:04, Jared Cabot <jaredcabot at protonmail.com> wrote:
> 
> > Latest update.
> > 
> > Looks like I'm getting 2.76VDC out of A7J1 and I can't adjust it with A7R3. According to the manual, it should be less than 50mV.. I was able to set this to around 0.5mV previously, so it did work at one point.
> > 
> > Q1 and Q2 test ok on my ebay component tester, IC1 is a selected uA741TC, but I'm not sure how to effectively test it.
> > 
> > (I attached the schematic, hopefully it shows up ok).
> > 
> > Jared
> > 
> > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > 
> > On Thursday, December 2nd, 2021 at 18:57, Jared Cabot via time-nuts time-nuts at lists.febo.com wrote:
> > 
> > > Well, it seems more digging is needed... I have 84uA Photo I coming from the RVFR on A7P1, but the front panel is at 14 (Should be 42 for my Photo I level)
> > > 
> > > Manual says look at Q1, Q2 and IC1 circuits. Anyone have any pointers or suggestions on what to check?
> > > 
> > > Jared.
> > > 
> > > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > > 
> > > On Thursday, December 2nd, 2021 at 17:21, Andy Gardner, ZL3AG via time-nuts time-nuts at lists.febo.com wrote:
> > > 
> > > > Don't give up now, Jared! You must be so close to getting that puppy running correctly.
> > > 
> > > > On 2/12/21 9:16 pm, Jared Cabot via time-nuts wrote:
> > > 
> > > > > Well, yay...
> > > 
> > > > > I put the OCXO back in the 5065A, and got a good 2nd Harmonic reading. So I started going through the alignment procedures and somehow I now have no 2nd harmonic again, and I can't get it back...
> > > 
> > > > > I'm starting to lose interest in this thing, seeing as I have the Leo Bodnar GPS standard anyway that I don't have to sit for hours twiddling dials and poking things just to get it maybe sort of working.
> > > 
> > > > > I might give this one more chance before I sell it off to someone with a little more patience, or who prefers fixing gear instead of actually using it. I think I've had this thing working for all of a couple days in the months I've owned it, whereas the GPS standard is the size of a pack of cards and has never failed in the same time.
> > > 
> > > > > Jared.
> > > 
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