HP 8552A / 8554L Spectrum Analyzer help request

[RobGT390]

Hello !
I have recently bought the above mentioned analyzer, it has been unused for many years and despite being told it was in working order I realized something was not quite right with it when I went to view it, I was going to walk away but the seller dropped the price so I thought I would take a gamble and see if I could repair it. I just love the old HP gear. It`s my first ever spectrum analyzer so I am in at the deep end.

When first switched on it appears to function normally and scans in all scan time ranges, it displays the 30Mhz calabration signal and the harmonics but after about 45mins of warm up time it will only scan when set in 0.1 to 5 mil/s range and the uncal light stays on, if I select any scan time range greater than that the uncal light goes off and the unit stops scanning, all I get is a 1" tall vertical line at the left hand side of the display. I am not sure where to start with the diagnoses so was hoping someone here might be familiar with these old units and might be able to suggest what area would be best to check first
I have removed the IF and RF units and separated them to clean the connector sockets and plugs, and cleaned the contacts on the rotary switches but still the same results
best regards
Rob

[factory]

Have you checked to see if any of the power supply rails are missing or have changed when the fault occurs?

David

[RobGT390]

not as yet David, I have just have managed to find the service manual on the HP archive and am reading through it, it definitely seems to be influenced by temperature as I have no heat on in the workshop tonight and it has dropped to -2c outside tonight, it`s pretty dam cold in here too, and when the temperature dropped the analyzer has started to function again !

[factory]

Make sure you have the correct manuals for the serial prefix of the modules & display unit, HP often made design changes over the years.

I don't know which display mainframe you have, but power supply faults are one of the common failures with them, I've got an early 141T here that has had a complete replacement (much later) PSU board when it was serviced by HP at some point in it's life, so that will be extra confusing when I get round to looking at it. I also have a 141S & another 141T that are working.

David

[Radio Wrangler]

Start with the power supplies. Number-one suspect when several things seem to go wrong at once.

If your mainframe has a storage tube, you'll need to take special care to avoid damaging the tube. They can be ruined by incautious setting of the front panel controls. There is no protection against this. Consequently the number of properly working storage frames is a bit low. The best frame has a normal CRT with a dual phosphor, fast blue and a yellow afterglow. They seem to last well.

In some 140 series PSUs the references are neon bulbs, not zeners. They can go bad over time.

David

[RobGT390]

The mainframe is a 140s. I don’t know if that has a storage tube or not, only manual I could find for the mainframe was for a 140t and I am not sure of the differences, my +100, -100, 250 and 12.6 DC voltages are all present and correct but unable to check the -2350v as I don’t have a high voltage probe yet. Looks like the neon type mentioned above. Looking at the 8554l manual and following the trouble shooting it suggests my problem may be on the scan generator board, I took a look at it and noticed a transistor has been changed previously, I also spent some more time on the connector sockets getting them really well cleaned, when I put it back together the problem was actually worse, only working on .5mil/s range. It’s a real pain the in way it’s built requiring extender cables and board extenders to service it.. which I do not have. I have tried to find the cinch sockets and plugs to make up an extender cable but had no luck so far

[Radio Wrangler]

You're making progress.

in these circumstances, there is a workaround for not having extender boards. You want to monitor a couple of points on the board? Solder on a couple of wires you can lead out through vent holes and reassemble. With the covers off the 140 you should be able to thread them outside and get scope probes on them.

Slow, tediously slow, but it works.

David

[factory]

Ah 140S, I should have guessed with it having the earlier 8554L plug-in, I may have the manual for the 140S, as I fitted the CRT from one to a standard 140A.
Have a look at the later 140A oscilloscope mainframe manual (probably the one that mostly uses silicon transistors), the 140S mainframe is a modification of that with the P7 CRT with spectrum analyzer graticule, the only electrical difference I noticed was one less connection to the CRT.
But from what you've checked it sounds as if the PSU in the mainframe is working.

David

[factory]

I checked and it appears I don't have the 140S manual (but do have three different 140A manuals), how I found out the spectrum analyzer CRT I bought was correct I don't know.

David

[RobGT390]

Ok thanks David, I had a little time at it this evening and again cleaned the contacts between the IF and RF units, it worked on a few ranges from 0.1 to 5 mil/s but nothing over that. I went back to it once it had warmed up a while and after a time it started to try and do something in the higher time settings, instead of the blank graticule I started to see a little flash/flicker much like a fluorescent light tube as it starts up, eventually the flashes became longer and then it started scanning, this process repeated each time I moved up the time settings until eventually it`s now scanning on all settings again right up to the 10sec per division. One thing I have found is the 1v and 10v calibrator outputs on the 140s are pretty much half what I guess they should be (.553v and 5.43v)

[factory]

What did you check the calibrator output with? It should be a 1V & 10V peak to peak output, these are intended for the oscilloscope plug-ins, when they became obsolete they removed the calibrator function from later spectrum analyzer mainframes.

David

[Radio Wrangler]

There is an RF calibrator output on the spectrum analyser RF plug-in. Something like 100MHz at -30dBm

David

[RobGT390]

Well... progress, I removed the 8554L RF unit and powered up to gain access to check the -10v and +20v on the 8552A sub power supply board, I was quite surprised to find the unit was now scanning on all time ranges, nothing on the display of course as the RF unit was removed, but the scanning lamp on the IF unit was coming on to indicate a scan was taking place, so I had a peep inside the RF unit. It had calibration security stickers over the screws so the cover has not been off in a very long time, I removed the boards to inspect them and noticed the YIG power supply board has had quite a bit of re-work done at some time. Looking closer I spotted an un-soldered joint ! I think someone had lifted a leg of a component during the previous diagnosis and forgotten to re-solder it. So all back together now and it seems to be working ok. Lord only knows how long its been like that. On to the calibration now and fingers crossed that will go ok. Thank-you so much for taking the time to help me diagnose this unit and offer support.

[factory]

That would certainly explain the intermittent fault you had at first, hopefully that is the only problem.

David

[6AL5W-Martin]

this is the long time without RUN.
Use it monthly, so it will be always fine.
When the day has come it blow the both Fuses at back of the IF, there is on the (not shure..) second card from backside, 2 gas stabis on the board, they become tired, then it blow the both fuses als following of the crowbar protection.
It is near to impossible to find 103 Volt Gas Stabis, so I used 2 pcs ZZ1000, each in series with a BZY 22 Volts Zener Diode. This combination delivers exactly the 103V and the temperature walking is near zero. A 100v zener without Stabi ist nightmare, here not possible.

The S is more cute then the T. And yes, it is a storage, with a round screen

[Radio Wrangler]

With an HP storage scope, ALWAYS set the trace brightness in one of the storage modes, NEVER in 'Conv'

In 'Conv' you cannot see when you have the beam current too high and flaring occurs... it's easy to have the beam current high enough that it eventually physically cuts through the storage mesh.

There is no protection on these things. Tektronix were a bit cleverer in this area.

With a spectrum analyser, I suggest you use it in storage mode only and just turn the persistence control low so you don't get multiple trace build-up.

HP CRTs are completely irreplaceable, especially storage ones because people can easily ruin them. There aren't many storage mainframes left in working order.

David

[6AL5W-Martin]

thank you for tips David

Here is a picture from the S,
the 110MHz plugin and a wire as antenna
the switching pos is "write"
I use it mostly for something around radio.

[Radio Wrangler]

That 110MHz RF section is a peach.

THere is a matching tracking generator which also includes a Nixie tube display frequency counter. You can use it to pause and count the analyser at a chosen marker point so you can very accurately establish where things are.

I used such a setup for years doing filter development. It has the cleanliness to see well down filter skirts without reciprocally mixed pjase noise intervening.

The 1250MHz plug in uses a quite different tracking generator.

David

[6AL5W-Martin]

I have only the 100MHz plugin and a LF with internal tracker.

[Nymrod121]

Originally Posted by 6AL5W-Martin

thank you for tips David

Here is a picture from the S,
the 110MHz plugin and a wire as antenna
the switching pos is "write"
I use it mostly for something around radio.

Super photo - and a great website Martin
I have the same model of Tektronix 'scope trolley as shown on your website homepage Mine is awaiting the return of a 465B which is on loan to a friend. Until that one returns, the trolley is holding a He***** Pa****d 1740B ...

M.f.g.,

Guy