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Re HP 478 A Thermistor mounts could someone –please direct me to a listing of the different options for example HP 478 A - H75 also interested in any one that uses the H75 option Regards Paul

If anyone has a copy of the manual for this old amplifier I'd appreciate a copy. Even just the schematic diagram would be appreciated. I have had this amplifier for years and use it once in a while. There's a DC offset on the output now but appears to have low distortion. Ran on mercury batteries. Now the battery contacts are all corroded so I just connect a power supply to the test sockets. Has germanium transistors and I think it is '60's vintage. 10 Hz to 1 MHz is its frequency range and has 20 dB and 40 dB selectable gains. I did check the files. Thanks! Pete

Hi all, Over the weekend I've got a couple of 54512Bs at my desk to seek to bring back to full functionality. My main scope is a 54522A, and I assume they have some commonalities, but I've yet to open mine (it came to me fully refurbished and never needed to open the case). I'm not very familiar with this other series, and hope on some good input and recommendations. The documentation is not as good as others I've seen from HP. Specifically for this unit (54512B), Keysight only seems to have a very skinny (by HP standards) Service Manual which can't honestly be called "module-level Service Manual," as it doesn't really into much detail on the different modules. Then there's a "Front Panel Reference," which is an odd other way of naming what I think is the Operating Manual. A couple other manuals have to do with programming. That's it. Sometimes in a series you have to look for the main unit, but in this case I'm not sure that's the 54501A, as the catalog spec sheet seems to suggest, or the 54505B, as per the SM. Maybe someone very familiar with the series would know. Artek doesn't have manuals for the 54512B at all, but they do for the 54501A, and if applicable, I'd get the series of six manuals they sell as a bundle. If no go, I'll be a bit in a bind with fixing this given what I have at hand. I am aware HP was not longer offering component SMs by this point, though I don't know for a fact on this specific series and scope (but I do regarding the better?/later? 54522A). Is this really capable of FFT to 500MHz, even if the scope is rated to 300MHz? I can't make sense of that. Now, on to the specific issues with the units. Unit #1 (S/N: 3214A00705) Upon starting it, it reports something like "TRYING TO START REALTIME CLOCK," which is unsuccessful after a time countdown from I think 60: "REALTIME CLOCK FAILED TO START - DISABLED." Once I get it to display the default screen and output a trace, it stated "Default cal loaded. Re-cal instrument." Self Test passes all. I'm also seeing a solid and apparently accurate 5V from the DC Cal output in the back. I haven't tried the AC Cal output. Note this one had the Cal switch in the back in the UNPROTECTED position when I got it. I'm able to display the square wave test signal from the front panel. Unit #2 (S/N: 3214A00704: consecutive units!) Upon staring it, it stated "CALIBRATION FACTOR CHECKSUM ERROR. MOVE REAR PANEL CAL SWITCH TO UNPROTECTED. POWER INSTRUMENT OFF AND THEN ON AGAIN. RE-CAL INSTRUMENT." It also says "Trying to start realtime clock (09290)." Maybe that's an error code? Upon switching the rear Cal switch to UNPROTECTED, it boots successfully, goes to a default measurement screen, but gives me a warning "Failed interpolar cal." The trace seems to jump around on Y a bit. Self Test passes all but Timebase. It also displays the same error as default screen ("Failed interpolar cal"). 5V out at DC Cal is good. This one had the Cal switch in UNPROTECTED position, so maybe that's why it booted successfully. I'm able to display the square wave test signal from the front panel, though it seems to be offset vertically a bit. To me, this seems to tell me the battery holding the cal constants is done - going by what I know about my 54522A. It's also possible some Dallas RAMs are out of battery - though I don't know if this uses those for non-volatile memory. I have not yet opened the units, so I've no idea where the rails are, if any caps have leaked, etc. But maybe the information above gives some clues on what's going on, enough to start thinking on it. It also seems the issues are shared very similarly, so maybe that's making the repair more streamlined. Looking forward to your input. Thank you, Radu.

Hi everyone, I am looking for some help on the repair of my 8753 VNA. I took some time trying to find the problem it myself with the service manual without success. The unit was working great and failed during my last filter mesurement. The signal is now noisy on port 1 and 2 (in S11,S22 ans S21), even if I do a new calibration. I have no error on power on. Have you ever entered this type of failure ? I was first thinking of an ESD failure but it do not seems to be the case. The two input couplers mesure OK. I have 16 dB of coupling loss on port 1 and port 2. Visual inspection do not show any damage on the RF patch. The solid state switch also seems to be OK. I have 2 dB of loss between the input and the two output of the SP2T. In span zero mode I mesure a RF signal at the right frequency in the 1 MHz- 6 GHz band. Output power is also OK. The stepped attenuator seems to be Ok, signal source is there. The only problem I can see here is when I look at the RF out signal on a spectrum analyser, the RF signal do not seems to be locked. When I reduce the SPAN on the VNA, I can see a lot of spike on the response. From what I understand, I now need to check the A7 Pulse generator diode stage and the A11 Phase lock board. The red LED on the A11 board is blinking but do not stay ON. Could you help me from this point on this repair ? Thank you ? S11 signal, port 1 open SPAN 6 GHz: S11 signal, port 1 50 Ohms load, SPAN 6 GHz: S11 signal OPEN SPAN 1 MHz S11 Signal SPAN 6GHz with 50 ohms load

My HP 8660B/86602B (owned since 1995 - I've owned it longer than it's initial life in industry, I believe) failed to produce a stable output signal when powered up a few days ago (it has worked properly over the years, although it's use is not frequent.) I wish to tackle repair (at least as a learning experience.) When tested today at some spot CW frequencies (1, 2, 5, 10, 20, 30, 50 and 100 MHz), output signal is below nominal by 200-300 kHz and is not stable (movement around carrier seen on spectrum analyzer display and listing on a receiver yields a noisy and unstable signal.) A swap-out of the 86602B RF plug-in (I have a spare) yielded no difference in behavior. I have original operator/service manuals for the three key components (the 8660B, 86602B and 11661B frequency extension module inside the 8660B) and associated extension cables/boards (the 11672 service kit and 08660-60070 extender card set), so at least not flying totally blind. My getting-started question is from this observation: The 8660B manual's adjustment/test procedures don't mention whether the 11661B frequency extension module's behavior should be considered (as far as I can see, there is no mention of the 11661B in the 8660B manual at all.) It appears to be silent as to whether the 8660B should be evaluated with the 11661B installed (or not.) The 11661B manual focuses on that device and presumably assumes that the 8660B containing it is working normally. Where (at the 8660B itself or the 11661B FEM) should I start troubleshooting? Thanks for any suggestions (other than recycling the hardware and replacing it with a TinySA or similar)!

I have several instruments, in particular HP6645A power supply and HP4263A LCR meter, that use LCDs. They would benefit greatly from a backlight in my lab environment. Has anyone come up with an easy way to add such? I need to open up the 6645A for another reason soon anyway, so might as well do any backlight kludge while I'm in there. Steve Hendrix