Products > Test Equipment
Test Equipment Anonymous (TEA) group therapy thread
bd139:
I wish I had the room and the air con for a 547 ;)
med6753:
--- Quote from: bd139 on June 03, 2018, 10:46:55 am ---I wish I had the room and the air con for a 547 ;)
--- End quote ---
Got the A/C and in the winter I could save on heat.
Room? No problem. Kick the OS-245(P)/U off the cart and hoist up that bad boy, although it would be a tight fit. :o
Berni:
So i have taken on figuring out what went wrong in my Tektronix AWG2041 signal generator.
First thing as usual is have a look trough the service manual for any troubleshooting tips. Flowing the troubleshooting flow chart only got me to a suggested solution of "Replace power supply module". The bastards didn't even give me any pinouts on the PSU or any of the boards even. On top of it they use 0.1 inch headers for a few connections that can be plugged in backwards. Someone already was in here so all the connectors had some stripes painted on to indicate what way around they go back together, but i take photos just in case.
Once i get it out however...good lord. This has to be the most complicated PSU i have ever seen in a piece of test gear. Look at the thing!
Its made up from 12 circuit boards! The heatsink is made from 6 aluminum parts screwed together in various spots. The massive output connector has 22 pins, but also has 3 other power output connectors scattered around. :o
How the hell am i gonna fix this over complicated mess of a PSU without any information about what it is supposed to do even.
Once i got the board out i could start tracing things out a bit. Its quite well designed electrically but not so mechanicaly. I figured out the topology of it and found out they have a solid state soft start cirucit (triac i think) that powers up the unit with 12 Ohm in series with the mains at first. The soft start resistor was blown open circuit so that's why it did nothing at all. Later on that fed a boost converter with a giant toroidal inductor to create the PFC circuit. Turns out the power MOSFET in that circuit measured low resistance across all pins. So this is likely what blew up the soft start resistors. Since the PFC circuit is likely not critical for it to work i simply removed the faulty transistor but put the diode and its heatsink back in so that power would still make it trough the PFC. Power it on...aaand woho i get fans going and a picture on the CRT. I still quickly turned it off afterwards just in case.
So here is the part that broke it all. Its a 2SK1018 N channel MOSFET 500V 13A. It looks like an ancient part so il likely replace it with some modern equivalent.
bd139:
Damn I hate power supplies like that. On a positive note you can usually work out what each board is for rather than trying to divide the supply into modules. Good luck with the fix.
I’ve noticed the cheap Chinese test gear has some pretty simple and excellent performing SMPS in them. Far lower component count leading to easier reverse engineering.
med6753:
Holy crap! :palm: It looks like it was designed by an Engineer who took lessons from Rube Goldberg.
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