HP 8920B service monitor repair(It's Alive!)

[TheSteve]

Bought an HP 8920B service monitor for "parts" on our favorite auction site. It looked to be missing a few parts but was in very nice condition.
For those that don't know a service monitor is a single box that contains a RF signal generator, multiple audio generators, RF analyzer, audio analyzer, spectrum analyzer, dummy load etc. It can generate and analyzer signals at the same time. They are generally for radio alignment. In the case of this specific 8920B(they can have various options) it covers 0.4-1000 MHz and can handle 60 watts continuous, 120+ for 10 seconds in to its RF port. It has the spectrum analyzer and high stability reference options. It also has the signalling board which can generate and decode all sorts of analog audio data.
I've always wanted an 8920B and already have an 8921A which is quite similar so I figured I'd have a decent chance of repairing it.
Front:

Back:


It failed to boot in the pictures and was stuck at the bootloader.



When I received it I noticed that it was in very nice condition. I opened it up I found something which did not inspire too much confidence, this is a side picture of the chassis:



Wondering why it didn't boot I pulled the memory card and saw this:


That is a lot of empty firmware sockets! In my 8921A there are OTP roms installed on those sockets. The 8920B is supposed to be flash upgradeable though via a PCMCIA card plugged in to the front of the unit. I posted on the HP support group asking for firmware but nobody had it, and nobody could tell me what type of flash chips fit in the sockets. I traced the address lines and decided that 29F010 were the largest that could be addressed. I ordered a bunch of flash chips and also found a firmware update PCMCIA card on the same auction site I purchased the unit from. I waited for everything to arrive...

[TheSteve]

The big day finally arrived I had flash chips and a memory upgrade card.

I installed 8 flash chips and plugged in the firmware update card. I was greeted with this screen:


I went through the process and it completed successfully.



So far this was looking very promising. I followed the instructions and rebooted, and sadly was back to the exact same bootloader screen I had started with. I repeated the process but it made no difference. I then removed one of the flash chips and dumped it, it was totally blank.

At this point I decided I had to think about it a little more.

More to come...

[mrf245]

http://www.keysight.com/upload/cmc_upload/All/8920_Component_Level_Information_Packet.pdf
This diagram shows a little different A8 memory card than you, it used DIP EEPROMs.
If upgrade process successfully finished, I suggest check if VPP supply to ROM is OK
Or you just no to plug any ROM chip and execute upgrade to see what happen?

[TheSteve]

OK, lots of updates to give on this 8920B.

I had another look through the service documentation I have and came to realize those sockets are supposed to be empty on an 8920B. On the 8920A and 8921A the sockets hold 27C040 OTP chips for the firmware. On the 8920B it has a different processor board with flash memory directly on the board. So that explains why the firmware upgrade worked, but not why it didn't want to boot. I have since done a lot of work on the unit and found many bad cables/components. Here is the summary:

-A5 Serial I/O controller - resoldered to fix(this allowed the unit to boot, but it had many errors)
-Bad DB15-IDC14 cable going from motherboard to A23 input module - Used new ribbon cable and carefully recrimped the existing connectors to it
-bad cable going to front panel - again reused the existing crimp connectors and made a new cable
-CRT kept shrinking - removed CRT module and found a fuse that was loose in its holder. Gave the holder a little crimp and it is good again
-Frequency counter failed self test. Found a bad 3906 transistor in the counter interpolator portion of the A19 measurement board
-GPIB didn't work. Found two pins shorted on the GPIB driver IC. One pin and its PCB trace had been bent into the pin beside it. I carefully straightened the pin and pad
-Found pour rework with missing connections on the PLCC ram chips on the A20 display processor card - resoldered
-Found poor rework on the A19 measurement board, several pins not soldered on the main processor
-Noticed the A4 "Modulation Distribution" card had a huge X on it and said "SCRAP" same as the chassis. I see it has had some rework done, I cleaned it up and so far it seems to work
-Rigid coax line jumper W13 missing - made a replacement using a piece of rigid line
-Rigid coax jumper W9 missing. This is a right angle SMC connector to a bare line which has a right angle with the rigid line plugging directly into the PCB. I don't have a right angle SMC connector so I used a piece of rigid line joined to some coax with a right angle SMB connector. This line I would like to replace with the proper one at some point.
-Two open ports on the back where options can be installed. I cut pieces of aluminum and made proper filler panels.
-Antenna in and Duplex output BNC connectors are worn on the outside. I have ordered a replacement input module from a similar unit to steal the BNC connectors from.
-Parallel port was loose - internal nut was missing, added one in so the port can be used again

So with all of that done the unit seems to operate properly. All RF and AF tests are now passing and I've not found any functions that don't work. Hard to believe something else won't pop up but its been solid for many hours and power cycles now.

Some various pics:

[TheSteve]

These pics show my home brew replacement line and the proper rigid line with the right angle SMC on one end.
Anyone have some rigid line with a connector that might work as a replacement? It turns out doing the 90 degree bend is quite easy, as is cutting it to expose the center conductor and insulation.

[TheSteve]

Some various screens

[MattSR]

Great work there, Steve. I love the old HP gear and it seems to be quite bulletproof in some ways...!

[mrf245]

Nice! You have done a lot of job on it.
So finally how it can boot up normally? You pull out ROM in sockets and re-upgrade again?

[BFX]

Really Great job  I like this repairs.
Thank you

[SaabFAN]

I'm also curious about these monsters. There's a reseller here in Germany who has 8922 constantly on sale for 349 + shipping. Tempting

Can you shoot some videos to show how it works? Maybe do a teardown/review (or send it to TheSignalPath XD).
There's really not a lot of information about these devices available and from what I read in the manuals and advertisements, they seem to be some kind of a jack of all trades. Question is: Is this correct, or are there some really nasty traps and shortcomings when using these devices for general purpose applications?

[TheSteve]

I'm not really into doing videos. These units are too heavy/expensive to ship around. The 8920A/8921A/8920B are all very ideal for radio repair. You need to be careful with the options they have depending on your requirements. Some aren't spec'd to operate below 30 MHz, some can only handle 4 watts of input. On the 8920A/8920B the spectrum analyzer is an option etc.
 
The full list of primary functions is:
    AM/FM signal generator
    AM/FM modulation analyzer
    Duplex offset generator
    RF power meter
    RF frequency counter/frequency error meter
    Audio frequency counter and power meter
    AC/DC voltmeter
    SINAD/SNR/distortion meter
    Two variable frequency AF generators
    Digital oscilloscope
    Built-in IBASIC controller
    Spectrum analyzer with tracking generator
    Adjacent channel power meter
    Signaling encoder and decoder
    High-stability timebase
    DC current meter
    HP-IB/RS-232/parallel remote interfaces

You can find more info on amtronix.com which is a site run by a guy who repairs all of these units. His prices are pretty high compared to surplus/auction units but he has lots of valuable information.
http://www.amtronix.com/diff.htm explains the differences between several of the common units but doesn't cover the 8922.

They are an amazing work horse of a unit if you're into any kind of rx/tx repair below 1 GHz.

[TheSteve]

Nice! You have done a lot of job on it.
So finally how it can boot up normally? You pull out ROM in sockets and re-upgrade again?

Turns out the sockets are supposed to be empty - they are unused on the 8920B version. The main CPU board has its own flash memory which holds the firmware. The unit wouldn't boot because of a bad serial IO card. Once that was repaired it was able to boot from flash memory.

[mrf245]

I'm also curious about these monsters. There's a reseller here in Germany who has 8922 constantly on sale for 349 + shipping. Tempting

Can you shoot some videos to show how it works? Maybe do a teardown/review (or send it to TheSignalPath XD).
There's really not a lot of information about these devices available and from what I read in the manuals and advertisements, they seem to be some kind of a jack of all trades. Question is: Is this correct, or are there some really nasty traps and shortcomings when using these devices for general purpose applications?

I think 8922 series are not suitable for general purpose applications, some test only designed for GSM/CDMA band. If you can find HP8924C, its OK, almost same as 8920 series but include CDMA test.

[falcao_br]

Hello friends of the forum. my name is falcao_br I live in Brazil and I would like to know if any of my friends can help me with the question below

I have an hp8920a, but the same error message 200 ( duplex ouver power )

I would like to correct the error but in my country there is no repair support

Thank you very much in advance...

About Me

[TheSteve]

Hello friends of the forum. my name is falcao_br I live in Brazil and I would like to know if any of my friends can help me with the question below

I have an hp8920a, but the same error message 200 ( duplex ouver power )

I would like to correct the error but in my country there is no repair support

Thank you very much in advance...

About Me

Welcome to the forum.

Do you get any other errors? You might want to check the cable from the IO module to the main board.
You can find service documentation here:
https://www.keysight.com/upload/cmc_upload/All/EPSG072204.pdf

[falcao_br]

I thank the attention..
I will be very happy to be able to repair this unit with the help of colleagues ..
remembering that I am amateur radio in Brazil. (electronic lover)
and I need this equipment for my simple workbench
I'll check the information.
I'm sorry for my simple pronunciation
I'm using googgle translator for such communication

Follow error photos

[falcao_br]

Hello everyone..
I would like to ask for information about the voltages of the J6 connector (hp8920a)
these were the ones I collected on my HPP820
DB15- (1-15)
1 - 5.ov
2 - 5.0v
3 - 5.0v
4 - 11.85v
5 - 0v
6 - 5.0v
7 - 5.0v
8 - 5.0v
9 - 0v
10 - 0v
11 - 0v
12 - 5.0v
13 - 42.75
14 - 12.28v
15 - 12.31

I am in doubt because after a check on my hp8920a the voltages do not match
Can you help me?
Google Tradutor para empresas:Google Toolkit de tradução para appsTradutor de sites

[The Other John]

Hi, i have one of these too, have you tried connecting the CRT Video Out up to a monitor yet? I have but i get no video signal even though my CRO shows that there is a signal coming out, perhaps an inverted signal.

Would like to get this feature working.

Regards,
John

[TheSteve]

It is not standard video - you need a very specific monitor to use it or an adapter to convert it to a known/standard video format.

[MattSR]

The FPGA based GBS-8219 video converter on eBay can sync to the non-standard speed of the HP 892x series video outputs and convert to a bunch of other handy formats.

[VE2UM]

THANKS SO MUCH !!!!!

I am working on HP 8920/8921's and hadn't any detailesd shematics...

73 de Normand VE2UM

[VE2UM]

Just to add a helpful hint...

Reference oscillator calibration (will require a GPSDO or other known accurate 10 MHz reference):

Turn on instrument and leave on until full warmup.

Connect DUPLEX OUT and reference  to a scope for a Lissajous figure.

Setup 8921 to generate 10 MHz, level at -20 dBm and all modulations OFF.



Blue - CONFIG

SERVICE

Latch: Refs_DAC_coarse Ajust "Value"
       Refs_DAC_fine   Ajust "Value"

...to obtain a fixed Lissajus loop.

Refs_DAC_coarse and Refs_DAC_fine are now set but not "permed" in 8920's memory.. 

----------------------------------
To save:

TESTS

LOAD TEST PROCEDURE:
Select Procedure Location:

---> ROM

Select Procedure Filename:

---> PER_CAL

---> (k1) Run Test

 (May take some time...)

=> Timebase Reference Using a Counter

---> (k3) Select

---> (k3) Cal

---> (k5) Exit

---> RF Gen

Cycle unit's power.

[VE2UM]

Hi...

In most cases, HP 8921 damages are caused by excessive energy in the DUPLEX OUT or ANT IN  ports.

But this time, the problem (5 dB attenuator not working) was caused by a defective Teledyne relay (K7) with an open NC contact. (relay PN: 432YZ_7486)

Replacement was not easy since the A23 PCB is rather thick and hard to heat.

Finally, with a hot air, i could remove the defective relay. Then, to mininise the PCB trace heating, i used a #76 carbide to gently, by hand, drill-out the solder without touching the via.

Replacement relay installation was made using 63-37 Sn-Pb solder (unit built in the 70's).

Final test shows perfectly working main step attenuator.

[mojoe]

Wow, that's a tremendous job on the repair. Congratulations on getting it working.

I have an 8920B, and love it. I got a good deal on one that had Option 55, which is hard to come by.  The "B" model went with electronicly switched attenuators as standard, so lost the ability to cover the lower frequencies. Option 55 gives that back, with relay switched attenuators. Other than that, the only real differences between the "A" and "B" models is more RAM, and the use of standard PCMCIA memory cards, as opposed to the proprietary Epson cards used in the "A".

As someone else mentioned, the video output is non-standard. If I remember, the horizontal sync is 19.2 KHz. Yes, the GBS converters work (mostly), to drive a standard VGA monitor. If you have an old CRT Multi-sync monitor, you can use that directly.

There is a Yahoo group that covers all of the similar HP units. I think the name is "HP8924C". Lots of useful info, although I haven't been on the group in a few years.

[TheSteve]

My 8920B has option 55 as well - a wonderful feature.