HP 33120A: GPIB HW or Noob error? - Page 1
Forum section: electronics / repair

author: Tony_G
author_rank: Super Contributor
timestamp: January 06, 2017, 06:37:40 am
content: Hi All,Doing a bit of dumpster diving has scored me an old HP 33120A. It seems to work fine with the exception of the GPIB port.Plugging it into my 82357B and trying to find it generates an error display on the 33120A display and going to the error message menu shows that it is a 420. This is a 'query unterminated' error but the scan process shouldn't cause that.Additionally if I try to send it a *idn? query I just get a timeout.Checking my 82357B and IO Libraries install against another instrument shows it working so I think the error is either in the 33120A or there is some config option that I'm unaware of.Any suggestions?Thanks,TonyG

author: deepskyridge
author_rank: Regular Contributor
timestamp: January 06, 2017, 02:10:23 pm
content: The 33120A has both GPIB and RS-232 interfaces, make sure the RS-232 is not selected. Also you could try using the RS-232 and see if it functions correctly.Gary

author: Tony_G
author_rank: Super Contributor
timestamp: January 06, 2017, 04:53:11 pm
content: Hmm I swear it responded once to *IDN? but since that I haven't been able to get it to respond at all on the RS-232 port.No amount of CTRL-C (supposed to be the equivalent of DCL in GPIB), Enter Keys, etc seems to prompt a response - in fact the only way I can get it to react to the serial port is to set the baud rate to an incorrect value and then the 33120A will beep and the error annunciator will show.No amount of power cycling seems to fix the issue.TonyG

author: MarkL
author_rank: Unknown
timestamp: January 08, 2017, 07:43:11 pm
content: Sounds like a nice a dumpster.On the RS-232 connection, the manual says the 33120A uses DTR/DSR hardware flow control (and not the more ubiquitous RTS/CTS). Do you know if DSR is true (DB9 pin 6 > +3V)? If it is not, no characters will be sent from the 33120A (user manual pg. 198). I assume you selected RS-232 from the I/O menu via the front panel (pg. 115).Not sure why the GPIB interface is not working. Could be something wrong with the interface. But I would first double check on the 33120A I/O config menu that you're using the right GPIB address for the "*idn?" test.The GPIB and RS-232 are both handled by the same communications processor (U903), so there could be something wrong in that area that's causing both to fail. It talks to the main processor through an optically isolated Tx/Rx, so maybe something is flaky with the data path. It's supposed to be checked during self-test at power up.I would try to get the RS-232 to work first before digging into anything else. It's connected directly to the comm processor, so whether it works or not could provide some clues on where to look next. Perhaps try some commands that set operating modes that you can see from the front panel. Maybe it's only broken for data coming from the unit.

author: coldframe
author_rank: Regular Contributor
timestamp: January 10, 2017, 12:15:13 pm
content: Hello Tony_GIn my case, bad solder jonit(crack, oxidized etc,)I had Resolder C1015, U1051,CR1051Always, the first step is the start from power supply diagnostics and debugcoldframe..

author: Tony_G
author_rank: Super Contributor
timestamp: January 10, 2017, 04:58:46 pm
content: Quote from: MarkL on January 08, 2017, 07:43:11 pmThanks Mark - I set that up but I didn't actually put a DMM on the pin to see if I was truly getting a signal there - I'll check that first.TonyG

author: Tony_G
author_rank: Super Contributor
timestamp: January 10, 2017, 04:59:50 pm
content: Quote from: coldframe on January 10, 2017, 12:15:13 pmThanks coldframe - Was the issue you were suffering the same thing as mine? Device working in all respects but just not communicating?TonyG

author: coldframe
author_rank: Regular Contributor
timestamp: January 12, 2017, 02:54:07 am
content: Hello Tony_GThe details vary, but you’d better check.coldframe.