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In this case, YIG-tuned oscillator. The subject was a 70900 local oscillator module that is throwing errors on startup. (and it's probably not his YIG this time)

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

"Chuck Harris" <cfharris@...> writes:

If you are in the USA, you will probably never witness
a Schaffner filter fail. If you are in 220-240V land, you
may not be so lucky.

When the filters fail, the worst that happens is they release
a little foul smoke, and sometimes a little tar. Both problems
are pretty easy to clean up... if they happen.

Being in the US, my policy is to leave them alone, and to
fix any that fail, when they fail. If I were in 220-240V land,
I would replace them on sight. The rivets are a simple problem.
Center punch them, drill them out, and use a fresh pop rivet
when you replace the filter.

I'm started to exchange these filters immediately before even connecting
devices to power. I'm often buying TE in the US, and what happend
several times now is that i thought "lets connect it for a short time
and see whether it works". I had it already two times that the filters
blew up a few seconds after i connected the devices. Likely because they
picked up moisture during shipment. I'm living in Germany which is 230V Land,
these days we have often 235V-240V line voltage.

In total i think i've seen now 5 filter blowing up. Not sure how many
filters i had in total, maybe 10.

Given that the filter is connected directly without any fuse to the
power outlet which usually has a 16A circuit breaker, i'm also a bit
afraid of the fire hazard.

/Sven

This is what happens when people don't quote what they're replying to, which is common when treating this mailing list as if it were a web forum. It really makes a mess of things.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

Hi List,

i noticed that my HP8340A output level is low in Band 0. Probably since
i bought the unit one or two years ago, i just never noticed because i'm
usually using this generator only when i need frequencies > 4GHz. This
time i wanted to calibrate the flatness on my 8563E and used the low
band. At 10 MHz level is ok, but there's a steady decrease in output
level until it finally reaches a loss of about 25dB. (See attached image)
Note that the vertical scale description is wrong, it's the absolute
level, not the loss/gain. I put in -20dBm.

I disconnected the SYTM input and outputs in the 8340A, and measured the
frequency response. See the attached image. The PIN Diode Bias is -1V
when in the high bands, +5.5V when in the low band. The Service manual
states +12/-11V, but carefully increasing that voltage with a power
supply didn't had an effect on the output level. I guess the PIN switch
is just toast, and there's nothing i can do except changing the SYTM?

SOT23 package or somesuch? Pretty big one ? Kidding aside: you can't solder what you cannot see. So get a stereo microscope if you want to handle these components.

Wilkk

well. in the wost case, YTO.

My 3458A had just arrived back from Keysight after replacement of the A3 board and they didn't change the mains filter so I guess they don't see the newer filters as being problematic. Although, the level of support from Keysight has seemed to have gone down these days - they didn't bother changing the snap-hat batteries either even though they were well past due for replacement.

I will also check C15/C16 to see if those have been changed; I suspect not. If they are RIFA I will definitely change those.

I should have mentioned in my original post that I live in 230V land and I have already directly witnessed quite a number of Schaffner filters and RIFA capacitors fail with the release of a lot of the magic smoke along with a revolting stench. All the failures I have witnessed so far have been the earlier FN323 and FN326 series with date codes ranging through the 1980s and 1990s.

These earlier Schaffner filters I replace on sight, along with RIFA capacitors,? but I am wondering if the more recent series from Schaffner had eliminated the? problem and don't need replacement.

Oops. I was just going through the schematics and turns out that the missing standoff in the RFI assembly I was describing earlier is what actually appears to connect the A2 board to the MT1 terminal of the Triac, so its HOT, and NOT ground as I was stating. As it says on the red cover, the whole RFI assembly is HOT. Would not want anyone to follow bad advice because of wrong information posted and ZZZZ!! Wish there was a way to post a couple of pictures here, but maybe I'll just upload some to my server and post a link.

Funny you mention the clear encapsulation.

So I have some RIFA's I ordered and received from digikey in 2018. I
saved them for a project in the original antistatic bag in a cardboard
box in the unlite closet. So no UV exposure. I keep my office
relatively temperature controlled because of the test equipment there.
Imagine my fascination when I opened the box last year and found that
they had cracked. Keep in mind this isn't a large sample size it's
just 3 or 4 capacitors but to me it says a lot. I don't believe the
failure mode for the RIFA's is heating and drying out or whatever.
IMHO the encapsulation failure is the root cause. I suspect the
acrylic has a lot of internal stress from a rapid curing process used
by RIFA.

-Evan Foss

--


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Well the power supply arrived last week, and if you guessed there might be a good chance of it being damaged during transit then you where right. The ebay seller did an absolute terrible job (he is blaming his "shipping manager" and "staff problems"). They shipped all of the 70+ pounds inside a flimsy cardboard box with very minimal foam padding on the sides. The box arrived with two gaping holes caused by the power supply biting into the cardboard while shifting around when the box was dropped, probably by an angry UPS employee, but can't entirely blame this person alone as the box was almost unmanageable. Heck the power supply alone is very difficult to manage around even by its handles, let alone in a small box that was just barely larger than the power supply itself. I can imagine this kind of weight stuffed inside a flimsy box and shifting around with every move would piss off any postal employee. I am currently in contact with the ebay seller, just sent him some pictures, and hope we will find a suitable resolution to all the damage caused by his total lack of any suitable packing ability, to say the least.

One of the front sides of the rack mount attachment area is now bent inwards, even the heavy duty aluminum could to resist the blow without buckling. The handle on the same side was also bent out of shape and very difficult to even remove due to both attachment screws had been sharply bent in an angle. The junction block on the back that is attached to the A3 board was completely bent upwards until it was stopped by the surrounding metal, and this also deformed to some extent, but at least did not break the Bakelite strip. I removed the board, which was kindd of a pain with the loopy strip in the way, and I'm going to try and bent the whole thing back into shape. The edge of the PC board where it is attached to was also somewhat deformed, it now has sort of a ripple along its side. But luckily so far no obvious broken traces or components, or the board itself, which seems to be very sturdy fiberglass. Other than that some other various dings, scratches and dents in various spots and on covers. Even the bracket that holds the AC input power cord was bent. At least the delicate meters don't seem to have suffered, and the four controls seem to be turning freely and feel smooth, although still would need to confirm they are actually working properly once I am able to test the power supply. Two knobs have broken tops, but that was the way they where being shown in the original seller pictures, and the other two surprisingly survived the ordeal just fine.

While I was turning around this monster to open it up for inspection, it sounded like there was a loose screw of something rattling in the rear area, but I looked everywhere and could not find anything, nor have it fall out. But finally found the cause when I opened the RFI assembly red box when I noticed that 2 out of 4 aluminum standoffs inside where broken off and rolling around freely inside the box, and of course only two screws holding the red cover in place on to the bracket, two has their heads broken off clean and the threads are still left inside the standoffs. Furthermore 3 out of the four threads of the standoffs are broken off very close to the end, so they barely are able to catch on to the lower set of standoffs, minus the washers that where also bouncing around. Biggest bummer I see is that the one standoff that can definitively not be refitted easily is the one that completes the connection to the chassis for the A2 board, so among other all of the three X caps have no return to ground, and of course nor the rest of the board itself. The red cover I am pretty sure is also not grounded if that standoff is not in place. Trying to figure out how to get the remaining thread that is left inside the heatsink to try and refit this very important standoff and complete the missing ground connection. Maybe I could try to drill it out carefully. At least its soft aluminum, but so is the heatsink as well, and I only have a hand drill although if I go slow and steady it will be fine. Otherwise have someone with a drill press that I might be able use. Any suggestions on how to attack this problem from another angle would be welcomed.

BTW all three of those bypass caps are showing quite a bit of crazing, one even has a sizable crack on the side, so will replace all 3 of them. Reminded me of those RIFA caps in the Tek 2465 scopes, exact same same problem. One of the electrolytic caps on the A3 board, Sprage 325uF 35V shows signs of outgassing on the + end, and I think it will probably also a good time to replace the other big Sprage 1400uF 30V cap. Also saw there are a couple of other smaller 5uF and one 20uF caps on the board, going to have to check them as well. Has anyone had to deal with these replacing these caps? I usually try to only replace caps that really are in need, over blanket outright replacement of all. BTW this power supply is serial number 2043A-04631, but haven't yet check to figure production date/age, and if its an earlier production oldie or a later specimen.

Finally, since I don't have 230V at my bench yet, was thinking of temporarily rewiring the power supply for 115V until at least I can test it and get anything that needs fixing done. I saw the instructions to do so in the service manual, among others will need to change some jumpers, the strapping on the main transformer, install R3 390R 2W MF on the A2 board and a few other things.

So that's it for now.

Yep, had a Schaffner, filter, fuse, switch combo on an HP 4951C released both magic smoke and tar 10 min after powering up this ebay purchase out of the US, on 240V in the land down under. Don't know which was worst, breathing the acrid smoke or cleaning the tar off of some of the components on the main PCB.

Regards,
Peter

I pulled the diodes up and checked them. There fine. The diodes Alexander suggested are next to impossible to install with normal iron. Hell I barely can see them. My soldering tip is bigger than the whole diode package . But I did find some lose sma connectors that I tightened up and on the cal data now goes down to -31 dbm, it was 104. I think I'm calling it good.? Here's a picture of that diode package I got from digikey.? That is 2 diodes in a case.?

Here is the dial on mine. But, I can only adjust to -130dbm, someone suggested a pin has slide out of it's hole preventing the last position.
I have yet to explore that.
????????????????? Mikek

I have figured out what is going on. The output attenuator vernier knob, when reduced towards minimum, cause the 0-3 level to light, and the 1-10 light to go off, this drops the output by 10db even after making the adjustment of 0db on the internal meter. Then if I rotate the vernier all the way to the right, the level changes, the 1-10 light turns on an 0-3 light goes off, now the output is 10db higher and is correct when the vernier is used to set 0db on the internal meter.
? I have been to many pages this morning and I saw one the said HP came out with a mod to get rid of this gain switching with vernier adjustment, but can't find it now.
Does anyone know about it.
?Any discussion about this to help me understand.
???????????????????????????? Thanks, Mikek

If the 10 db pad were stuck, the output would read +10, +10, -10, -10, -30 etc rather than +20, +10, 0, -10, etc

What's the -140 db position? My unit and photos on the web I see only have +20 to -130 markings.

John