HP Agilent 6632B showing CV and CC - Page 1
Forum section: electronics / repair

author: Astralix
author_rank: Regular Contributor
timestamp: November 16, 2024, 08:03:41 pm
content: Hi!I currently repaired my HP66312A Source Meter and as it was an easy job after finding out that only a Pico-fuse had ben blown forcefully by the crow-bar, I thought I check for my 6632B that is sitting dead on the shelf for a few years now.But the fault is a different one:When set to 0V the unit shows "CV" and about 0V and 0A (except the usual last digit flipping between 0 and 3)As soon as I program the unit to any other voltage, it immediately sets "CV" and "CC" and still shows ~0V and ~0A on the LCD.The service-manual 6632B only covers the analog section, as it was in the 66312A ones. The "Interface Board A2" seems to be identical on both units, probably the PAL and Firmware may differ.In the service manual is a scheme to follow for fault analysis, but it does not cover the CC + CV case.There is also a table of test-points to check, but they mention test-points that do not exist...So I checked some closest match, I could imagine:BIASTest PointDatasheetMeasurement+RailTP310 (R300)+38V 10%45V-RailTP311 (R303)-9.8V 10%-12.2V+5V secR317+5V 4%5.04V+12V secD470 cat+12V 5%11.71V+15V secR318+15V 4%14.9V-12V secD471 cat-12V 5%-11.83V-15V secR315-15V 4%-15.15VV_RefR475 (U400)2.5V 6%2.506V+5V intE3065V 3%4.98VExcept from the "Rails" everything is in tolerances. I checked the transformer twice, but the connections are correct for 240V unless there is an error in the documents.What I can observe is, that the 5V linear regulator for the "A2 Interface Bias Supply" is quite hot, but if the transformer is supplying a little more then expected, that would be okay.The IR cam does not reveal any heat source, giving a hint to a shorted Tantalum or dead IC.Also the U304 (7015) from the secondary bias supplies gets quite hot, but it does deliver 14.95V and the 7805 behind it does send out 4.95V.From the voltages I expect no harsh load on these.Next I checked the crow-bar logic, but it seem to be in off state.The output regulator transistor check out all good as well, there is also no short between the terminals and the fuse is intact.The service manual mentions the CV and CC symbols quite often and explains how these could help to identify an issue very easy. However, when I follow the diagnostic flow chart, I end on page 7 that says if CV is on and no output, change A2...That isn't really helpful, I guess...But the manual also tells to measure across the diodes that convert the anlog CC and CV signals to logic levels and this is like:Programmed to 10V / 0.2AOutput: Off, CV is shown:D328 = 0,58V | U306-3 = 0VD325 = -4.65V | U306-14 = 5VOutput: On, CV CC is shown:D328 = 0,355V | U306-3 = 0VD325 = 0.48V | U306-14 = 0VSo these logic levels do tell the logic to show a constant CV and depending on the ON state, an additional CC.The interface voltages from the service manual are all good except some I need to investigate further:SignalCV ModeCC ModeResult OFFResult ONOV_SCR*+5V+5V+0.68V+0.68VOV_PROG+3.9V+3.9V+0V+4.5VOV_DET*+5V+5V+0V+5VFUSE+2.4V+2.4V+0.51V+0.51VIMON_H0V+3.5V0V0VIMON_L+4.8V+4.8V+0.22V+0.22VVMON+4.8V+4.5V+1.7mV+1.7mVCV_PROG-4.8V-4.8V0V-2.4VCC_PROG-4.8V-4.8V-0.5V-0.5VCC_DETECT*+5V0+5V+5V0+5VCCN_DETECT*+5V+5V+5V+5VCV_DETECT*0V+5V0V0VFinally I tested the load function and put 2V at 0.2A from the 66312 to the 6632, but only a current of 44mA was flowing, regardless what I tried.I'll proceed with analysis but if someone came across a similar issue, I would love to hear about good ways for analysis and parts to check.And I'll double-check with the transformer setting, calculating 45V / 230V * 200V = 39V it looks like it is set for 200V instead of 230V. That isn't even an option shown in the service manual...Any ideas?Astralix