HP 8340B Repair. Anyone with Experience with Voltage Supplies? - Page 1
Forum section: electronics / repair

author: Flyingdancingfool
author_rank: Newbie
timestamp: July 18, 2022, 01:38:16 am
content: Greetings!I took out my perfectly functional HP 8340B by double tapping the plug in the wall socket. So far Ive diagnosed the problem(s) to the power supplies.Anyone have experience with 8340B repair?Kenn

author: Zenith
author_rank: Frequent Contributor
timestamp: July 18, 2022, 08:00:11 am
content: I've never touched an HP8340B.What do you mean by "double tapping the plug in the wall socket"? Have you given it twice the mains voltage it was set to?If you've done that and your luck's in, you will just have blown fuses. You may have damaged the PSU. If it's a linear PSU and you have the service manual, or at least a schematic, they are usually straightforward to work through. If your luck's out you will have caused damage in other parts of the instrument, maybe to hard to find and expensive hybrids etc.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: July 18, 2022, 10:58:47 am
content: HiPlease explain what you mean by "double tapping", Do you mean you applied 230VAC with the instrument set for 115VAC?Fortunatly it is a transformer type power supply so should be quite simple to repair, unless you have damaged the mains transformer.There is an assembly level service manual on the internet which should help you.G Edmonds

author: Flyingdancingfool
author_rank: Newbie
timestamp: July 20, 2022, 08:48:10 pm
content: Double tapping while plugging.Imagine trying to plug into the wall socket, and you are a spastic b@a$tard and you partially stick it in, then it comes out, then you complete the connection.All the while sparks flyI really screwed up!Kenn

author: Zenith
author_rank: Frequent Contributor
timestamp: July 20, 2022, 09:41:39 pm
content: Thanks for making that clear.I really can't see why pushing a plug partially in, and having it pop out (I can't see that happening either) and then thumping it home, should cause problems, much less sparks. This sort of mains supply interruption is going to take place in the course of power cuts, mains flickers because of lightning strikes and so on.Where were the sparks?Was the equipment switched on when you were having these difficulties with the plug?I suspect you may have a problem which arose coincidentally with the double tapping and you are being too quick to link cause and effect, and far too quick to blame yourself.Have a look inside the unit to see if there is anything obviously burned or damaged. Smell for anything burned. Have a look for anything which may have caused a short circuit. Check the primary of the mains transformer - I assume it's a linear supply - is it open circuit? Check the fuses. Take a known good mains lead, which doesn't need double tapping, power it up, and check the voltages to and from the power supply. Work through it systematically.

author: Flyingdancingfool
author_rank: Newbie
timestamp: July 21, 2022, 10:18:59 pm
content: Thank you for the suggestions, I think I got it.I bought some extender cards off of Ebay then used them to get access to the 150 Watt power transistors on the motherboard. I have this nifty transistor checker from P!ke in the UK, and I found a faulty A62Q3 Darlington transistor that regulates the +20V supply. This supplies a reference voltage to the +12, -5, and +5 volt supplies in a foldback current limiting architecture (at least I think).I replaced A62Q3 and tested. At first it shut down after 15 minutes. Bummer. Then I ran it again a few more times and at last check it was running for a total of six hours.So I am far from an HP 8340 expert, but a few extender cards, a multimeter, a transistor checker, and a tenacious can-do attitude sometimes gets the job done!Thank you again, let me know if your 8340 has problems, I can give you suggestions.Kenn