开云体育

So my trusty 2247A just turned off while I was using it. There where no puffs or cracks or smoke. It just quit and won't turn on anymore. Fuse in the back is good, and just in case power cord is also ok, so time to pull the cover.

After removing the processor board and the metal shield underneath I can see the power supply, last time was about 10 years ago when I replaced all the (total 17) ZM and/or ZS marked diodes with MUR160, and just C2204 the 100uF cap in the preregulator section with a 63V unit. None of the LV secondary supply caps where replaced as back then I tested a couple of them and they where all good and ripple of all the power supplies was way withing specs. On the board nothing looks toasted, burned or broken in there, no burnt smells either.

Dusted off my isolation transformer and after hitting the power switch I can see the fan briefly spinning up for 1-2 seconds and then stopping, and after that I can also hear a faint click like a relay clicking somewhere else (not on the PS board). Not sure what that can be, don't recall any relays in this scope but will check.

With 120VAC in from the isolation transformer measured 163V DC between the +DC and -DC test points, so primary supply looks ok. I can also measure about +40V DC at the 43VTP, a bit low but assume should be still within limits and pre-regulator appears to be working fine as well. I am also getting the same 40V on both sides of R2201 the 0.1 ohm resistor that feeds this voltage to the inverter switcher, so resistor seems ok, and no signs of overheating or stress on it.

Wanted to pull out the PS board, managed to uncouple the power switch lever although it is still in the way above the board, but for the life of me I cannot unplug the HV connector. Cannot remember when I did this about 10 years ago, if there was some kind of a trick or it just needs to be forcefully pulled apart. Is there a latch or something hidden on the connector that requires some previous operation before trying to pull on both ends? Since both parts seem to be rigid plastic don't want to force something to break. Can someone please confirm this just needs a good pull by the connector ends to separate, or what else?

Once I have the board out plan on checking the secondary PS rectifier diodes and the caps. None looks to have leaked at least not without pulling them, or have any bulges. Will also check Q2214 the inverter switching FET, which at least physically looks ok as they tend to crack when failing.

Any other suggestions from someones previous experiences dealing with this specific 224x power supply (not so much the similar but somewhat different in the 22xx scopes) would be appreciated.

Would also be interested in what supplies need to be loaded and recommended resistor values in order to safely test the board outside the scope, and yes I am aware of the HV plug and will take necessary precautions (and not with a lineman's glove!). Thank you.

Gave the HV connector another try and managed to separate it, and PS board is now out.

All LV filter caps tested good. ESR on all was between 0.12 and 0.14 ohm, values withing 10%. Not bad for capacitors that have been in service since 1986 or so.

Well still went ahead and fully recapped the power supply but still no change. And in the process managed to break the power switch link rod. How was I supposed to unlink it to get it out of the way I don't know as the access to the point at the corner where it couples into the shaft that comes out at the front panel is completely covered up by the chassis and the bottom main board which I don't think would be a good idea to remove just to do this. It would have been nice if someone could have explained the procedure to remove the power switch lever, but so far this thread seems like cricket sounds.

A cricket here, chirping in. Sorry to hear of the mechanical difficulties. I too remember being completely perplexed the first time I attempted to mechanically take apart a 2247A.

Do you have the service manual? Isn't there a processor routine that runs on start-up? Like a pre-flight checklist, where if all conditions aren't met, the machine shuts itself down?

And weren't there various firmware revisions for this product, where this start-up check routine could have been modified?

I'd guess that it certainly polls the MBU state. Could you have a dead battery?