HP 8753A Repair

[Timbo2020]

Hi all,

Just joined this forum hoping for some help repairing my HP 8753A VNA.

Bought recently at an equipment auction, last calibration says 2002 so I assume it failed before it's 2003 Cal.
Seals were unbroken so it never got diagnosed and sat unloved for 17 years.
Fan was clogged and seized with dust, now replaced and all cleaned out with compressed air.

Power on now shows what I assume is a checksum error (although it's a bit out of focus), I guess the EEPROMs have forgotten what they were told in 1986.

Is there an online depository of the software images so I might prog some new EEPROM's for it?
Or any leads as to how to fix it?

Thanks,

Tim.

[KE5FX]

Hmm, weird.  The 8753A firmware should be up on ko4bb.com but he's only showing the 8753C files, which aren't the same.  I'll re-upload it there, and also attach it here.

[Timbo2020]

Wow, that's awesome support :-)

Many thanks.

I'll get it loaded up and see what happens.

I expect to be back on here in a week or so with the next problem..

Tim.

[energy_hunter]

I fixed my HP8753D by replacing the EEPROMs found on ebay and from help from this forum. After replacing the EEPROMs on my HP8753D I then had to change a capacitor on the power supply. It was a bizarre problem but after powering on the VNA it would work once but then the display would be blank after a 2nd start. There seems to have been a power down problem/error catching routine that required a faster power down since the new capacitor was smaller than the previous one. This was hidden in the Firmware Upgrade instruction for the machine but I eventually found it and fixed my machine. Anyway, pls post your findings and hopefully we can help you out.

[Timbo2020]

OK so I replaced the EEPROMS, programmed with known good firmware v1.0

Whilst waiting for the chips, I realigned the HP1349A display with it's internal testcard. It's working great now, bright and focussed.

I guess one good thing about a 35 year old machine that's been presumed dead on a shelf for 18 years, is that the display is only 17 years old :-)

When I power on, with the new firmware, I get the same, one-line message as before.

E S@M G@IL!1=PQPQPQPQPQPQPQPG>m

I had guessed this was a checksum error message, thrown up by the boot loader?, but now it's focussed and readable, the message itself seems corrupted?

Pressing "Preset", I get a small "HP" logo, then the one line message again.

So the CPU appears to be alive and trying to run something...