Help! HP6632B control ok, output messed up - Page 1
Forum section: electronics / projects

author: babysitter
author_rank: Frequent Contributor
timestamp: February 24, 2013, 01:01:50 pm
content: Hello All,is there somebody who has fixed a few 6632B already?Mine was working well until today when I switched it on.The control logic seems to be OK, i can enter stuff and it doesn't behave too strange besides the output doesn't care.When started up with 0V set and "Disconnected" annunciator on, it has about 3.5V on the output and also shows the right voltage on display. Independent of the voltage/current setting, as soon as i switch output on it goes into protection and the voltage goes to around 0.9V (fan high). Rails are a bit high for this model, around +44 and -11Vrespectively.ATM I am babysitting and can't work too much on it. Any hints what I should look at first?(Time for "Sagans Club of diaper-wearing repair preventers" ?)Best regards

author: dimlow
author_rank: Frequent Contributor
timestamp: February 24, 2013, 01:31:38 pm
content: The first thing i would check is theThis

author: amspire
author_rank: Super Contributor
timestamp: February 24, 2013, 01:33:17 pm
content: I do not know this supply, but are the ouput/sense/etc links on the rear correctly wired? That would be the first thing I would check.

author: babysitter
author_rank: Frequent Contributor
timestamp: February 24, 2013, 02:00:13 pm
content: Little one is sleeping now, so update: Rails are reasonably clean on the scope, no shorted power transistor found (yet). Rails I measured at the rectifier diodes, Secondary I still have to.@dimlow thanks, your link was saved with (1), I am already busy with understanding the schematics.@amspire The sense was shorted to force, after partial disassembly its only connected by the internal available resistor connection. Correct metering gives me confidence that a lot of the logic board is working right.

author: babysitter
author_rank: Frequent Contributor
timestamp: February 28, 2013, 05:51:13 pm
content: Little one is quiet... continuing here !First, the "overvoltage" flowchart talks about desoldering, which I will not do due to solder fumes at home and if I have to desolder something, I will haul the device to somewhere else and solder there. But I have popped open a healthy unit and can provide the state of that compared to the fooling one. Different values from the healthy unit are noted with ().No overshoot on device turn-onUser interface seems OKFAN Control responsiveMeter voltage consistent with ext. DMMOutput voltage in "Dis" mode: +3,4..3.5V rising (healthy ~6mV)Shorting output now: 0,16V, 6.2A on meter. (Not done on healty, but...)Voltages:+RAIL: 44V (39V)-RAIL: -11V (-10)Secondary:+5V OK+12V A1 D470-C 11,4V+15V OK-12V A1 D471-A -11,4V-15V R315 OKV_REF OKInterface OK+5V OKR401 0V (seemed to be relevant to finding the fault location, so...)Aha! Q303 UBE~0,56V (Healthy: 0V! So there is something going on!)From here it deviates so much from the healthy one so i just describe the failing unit...Output on -->Overshoot 39V, ~3ms-->Annunciator "Prot" comes upOutput voltage in "Prot" mode ~0,8VMeter current 5-6AProt clear-->Current "OVLD", "CC" comes up but ovld persistent. no further overshoot, similar voltage as in ProtAny hints ? I would appreciate it !Mr. Babysitter

author: free_electron
author_rank: Super Contributor
timestamp: February 28, 2013, 08:55:54 pm
content: to troubleshoot this thing first disable its protection ( you can't really measure anything as the output shuts down in OV protect immediately )hold button 0 and 9 while turning on. the display will give some message with the model number of the machine.Use left/right to 'scroll' until it says No-PROTECT , use up/down to toggle it to NO-PROTECT <ON>hit enterCAREFUL ! NEVER EVER hit enter when it shows its model number ! Never ever change that model number using the keys !if you accidentally hit the wrong arrow key and that number changes : power off the machine and re-do the process...hitting enter stores the model number ( the firmware in these machines works for a range of machines.... ) and erases the calibration parameters...you said you see the output spike to 39 volts... that means the regulator is wide open .... check that darn jfet in the regulator loop.

author: babysitter
author_rank: Frequent Contributor
timestamp: March 01, 2013, 04:54:40 am
content: Good morning!@free_electron: Thank you for that advice, haven't realized the no-protect feature of the firmware, might save some soldering. Will not touch another feature. Darn jfet means Q316, i considered it harmless as I meant it is a part of the turn-on control only. Now that I have a healthy unit I can compare. I will try to find out more, many thanks for guiding me!

author: dimlow
author_rank: Frequent Contributor
timestamp: March 03, 2013, 01:58:26 pm
content: Quote from: babysitter on February 24, 2013, 02:00:13 pmYour welcome.