[FIXED] HP/Agilent 6624A PSU (the tank) HW ERROR CH3 - Page 1
Forum section: electronics / repair

author: pelule
author_rank: Frequent Contributor
timestamp: July 24, 2016, 11:51:07 am
content: I am using the "Tank" Agilent/HP 6624A as my preferred lab power supply since many years.The 6624A outputs can't be pimped to the front (despite notes on the WWW) thus I build an extender board to have the connectors close to my working area.This version of 6624A uses power modules instead of the discrete power fets.Advante: no high voltage on the heat sinksDisadvantage: difficult, to get replacement part if it fails someone in the future.When working on a project the tool suddenly messaged the error "HW ERROR CH3".The cause of the failure: a bad 30 years old!!! electrolyte (7.2mF/63V/build 1986).The sucessful repair I have documented in the attached file as it may of interest for the community.PeLuLe

author: Charles_z
author_rank: Newbie
timestamp: June 19, 2018, 01:28:44 pm
content: Many thanks to Pelule for these useful information! I just got a HP6624A which showed "HW ERROR CH4", and trying to repair it. I have downloaded the service manuals, and found it is quite difficult to follow. So far, I have a couple of questions and hope someone may help.1. The AC cooling fan is very loud. I noticed that when the fan was first powered on, it was quite quite and the rotation speed looked reasonable. Then, maybe a 30-40 seconds later, the fan speed increased and gave loud noise. Is the fan bad (bearing)? Or, is this loud noise has anything to do with the capacity near it? Any suggestion how to reduce the noise?2. When I turned on HP6624A, the screen directly displayed "HW ERROR CH4". According to the manual, it first should display "ADDRESS 5". Is my GPIB card also bad?3. When I turned on HP6624A, the screen directly displayed "HW ERROR CH4". I tried each key on the front panel, but there is no any response from the screen. Is my keypad bad?4. If I don't want to repair output board 4, can I use my 6624A with only 3 output boards?Thanks in advance!

author: free_electron
author_rank: Super Contributor
timestamp: June 19, 2018, 01:37:33 pm
content: unplug the grey communication cable of channel 4. the machine should power up.

author: Charles_z
author_rank: Newbie
timestamp: June 19, 2018, 02:02:32 pm
content: Thanks for the suggestion! I unplugged the communication cable of channel 4. 6624A powered up with the same message"HDW ERROR CH4" and then froze.Attached are two pictures showing the board4 (40W high voltage). The board only has 3 large Capacitors in the middle, which is different from the schematics in the service manual.This 6624A was manufactured in 1986 in US.

author: pelule
author_rank: Frequent Contributor
timestamp: June 19, 2018, 08:38:04 pm
content: QuoteMy 6624A does the same. It seems to be typical for that fan.QuoteMy 6624A showed error immediate also. It depends, at which step of the selftest the error is detected.Did you do "Test 1" in my repair doc - check if error is on the GPIB board or if the channel board is defekt?QuoteIf the 6624A is in the HW error mode, keyboard is ignored as it is a fatal error.QuoteIt is a 4 channel PSU, that's defined by the GPIB/Control board firmware. So NO, you can't use it with a defekt channel without replacing/changing the GPIB board firmware./PeLuLe

author: Charles_z
author_rank: Newbie
timestamp: June 19, 2018, 09:43:43 pm
content: Hi Perlule, I really appreciate your answers to my questions. Now, I will focus on checking board#4.I have been following your repair doc.Test 1 and Test 2 have been passed.In Test 3, I found the Reference Voltages are a little out of range. They are supposed to be 9.95-10.05 V. But what I got are 10.08-10.1 V. I haven't measured the VREF on Board#3 yet because accessibility issue. Is this 10.1 V a big problem? Should I move on to Test 4 on the power module U338?I just measured the fuses. And found F300, F301, F305, F306 are all bad. Looks like similar problems as in your repair docs. I will remove board#4 to check the capacitors.Update: I just removed board#4 and found the middle capacitor C363 7400 uF, 63V is shorted. Hope I can bring the board to work after replacing the 4 fuses and the middle cap.Thanks again!

author: pelule
author_rank: Frequent Contributor
timestamp: June 20, 2018, 04:25:44 pm
content: QuoteDepends on your measurement/condition.What's the resolution & precision of your voltmeter (to verify the Vref precision your DVM not to be better in precision)?Whas the system warmed-up long enough - I gues not. You may want to wait > 30 minutes power on before doing precision measurements (thermal stabilisation)QuoteCongrats - sounds like you have catched the root cause of the error (typical for old equipment).I recommend to replace all big the big CAPs an all 4 boards - they all have the same age, so issue could happen shortly again at another one.If you replace the fuses, replace them with the same value/type. That's important for a safe operation./PeLuLe

author: Charles_z
author_rank: Newbie
timestamp: June 24, 2018, 01:33:29 am
content: I replaced the middle cap (8200 uF, 63V) and the four 7A fuses today. "HW ERROR CH4" is gone! My 6624A powered up normally, and looks working normally on CH1, Ch2 and CH4.However, I found CH3 (high voltage 40W output board") showed -0.36V and UNR (unregulated). A brief check found Fuse F304 (120V-10A) is bad.I am now trying to remove Output board#3, and found it's kind of difficult because of the rear connection terminals. Looks like I have to remove all the cables from the front and lift up the board from the front. I will update soon.update: I removed output board#3 without removing the big cables at the front with some hassle. I found C361 (8200 uF, 50VDC) is shorted. Need to order from digikey again.