Hp 34401A ADDR 23 Error

[henas]

This Hp 34401a is my resent eBay acquisition. When turned on all segments lit and the unit gives one beep followed by “ADDRS 23” error. After short delay it goes back to all segments lit and followed again by “ADDRS 23”. This ~1.5 seconds cycle goes forever.
 
When Self test is invoked; first starts with beep and "Testing.." then relays click, after short delay the unit displays “Test Fail”. The “Test Fail” message is followed by all segments lit and “ADDRS 23” in never ending cycle.

I checked voltages: both 5V and +/- 18V all within spec and clean. 15V is OK and -15v is a bit lower -14.37V. No overheating. All caps OK, except for one with slightly higher ESR. It has been replaced but this didn't make any difference. I red about possible display fault as not communicating with main PCB properly.

Serial number starts with 31 so I assume this unit was manufactured in 1991.

Anyone had this problem?? Any input greatly appreciated.

[plesa]

Try to read error from remote interface by SYSTem:ERRor?. Maybe the RAM or ROM needs to be replaced ( U501,U502 and most probably U503)

[HighVoltage]

Could it be that something is wrong with the GPIB controller that is pointing to ADDR 23?
I have never seen such an error on the 34401A before

[henas]

Unfortunately I don't have GPIB interface on my computer to send the command.

I checked the reset line XPONRST and is set to high.

Is there a way to isolate GPIB from the system? How can I determine if the display is OK?
It appears my unit has older style display with one large IC.

[simmconn]

I suspect that ADDR 23 is not an error message, it just shows you that the GPIB address is set to 23 as part of the start up process, then the unit reboots. I would check the ground-referenced power supply voltages for dips and the reset/supervisory chip to the MCU.

[plesa]

Unfortunately I don't have GPIB interface on my computer to send the command.

I checked the reset line XPONRST and is set to high.

Is there a way to isolate GPIB from the system? How can I determine if the display is OK?
It appears my unit has older style display with one large IC.

You needs to have RS 232, SCPI commands should works. Problem can be to set the meter into RS232 mode instead of GPIB Adress 23.
Based on fact that you are able to run self test I will also try to set to factory defaults.