HP 8642B A19 errors - Page 1
Forum section: electronics / repair

author: analogRF
author_rank: Super Contributor
timestamp: May 23, 2018, 03:41:12 pm
content: I have got an HP 8642B signal generator off ebay. I was hoping someone could help me to find a solution to the following problem:The instrument gives a D75 error (test 1B of A19 module fails) at start up and when I run the Lock/Unlock test on A19 module (special code 358) it generates a whole bunch of Dnn errors (D4,D5,D6,D11, ....D34,D39,....etc)However, I cannot detect any obvious fault or malfunction at the output of the generator at frequencies above 1058MHz. Amplitude is ok, modulation is ok, sweep is ok, etc...or maybe I am missing something?I have the full schematics and service manual but descriptions of error codes are not in there.Does anybody know the description of these errors or at least what they are about generally?I have opened up modules A19A1 and A19A3 but nothing seems to be bad...the only thing I can detect by scoping around is that (only) when AM modulation is on, the ALC loop unlocks for about 55ms everytime I change output level such that an attenuator needs to be switched in/out. If no attenuator change is required, loop always remains locked. It does not seem to be unusual or abnormal to me because at those specific level transitions, when attenuator must change, the input amplitude to the module also needs an abrupt jump, so 55ms unlock seems normal to me....other than this I cannot see what these errors might be about. Is it possible that only the diagnostic reporting circuit is bad? That is just a DG508 analog switch thoughI emailed Keysight for help but the person came back saying he could not find any description for those errors.regards

author: Johnny10
author_rank: Frequent Contributor
timestamp: May 23, 2018, 05:10:10 pm
content: I had exactly same error when I turned on a recently purchased 8642B.For me the two RF switches were missing from the A19 board.Only discovered this by checking images posted online of the unit.Haven't worked on it anymore as other projects were first in line.My very short thread is on this site.https://www.eevblog.com/forum/repair/hp8642b-signal-generator-what-are-these-missing-parts/msg1507747/#msg1507747

author: analogRF
author_rank: Super Contributor
timestamp: May 23, 2018, 05:31:35 pm
content: Quote from: Johnny10 on May 23, 2018, 05:10:10 pmof course mine is not missing anything. as I mentioned, all output functionalities seem totally fine. without those attenuatorsthere is no output signal or it will have a very limited range in high power region (5dbm-21dbm or so) if they had bypassed the attenuatorsby the way, the A19 tests do not check on the attenuators at all, so even if you put them back in my guess is thatyou will probably get the same D75 error as I do. This has something to do with A19A1 or A19A3 board.

author: KC4Sw
author_rank: Newbie
timestamp: August 20, 2018, 07:13:09 pm
content: Good Morning, do you actually have component level schematics on the A19 module, if so is there a chance I can get a copy? I have 5 complete modules and 4 in-complete ones (plus multipuls of all of the other modules except the PS). All of the A19's present the same error you describe and as you also describe pass the verification test. this meas=ns the error has to be in the dignostic reply portion of the moduleat any rate any help is appreciatedsteve