Tektronix model 2220 power supply problem ...

Check R926, C925 first. Its common that the R increases in resistance and the C dires up. If this fails, it could result in such trouble. Check CR920 too. Measure voltage across C925, should be close to the indicated value and free of ripple, if not see above. Also check all other electrolytics, as usual (quite common to have them dry up by now).

If not, check the "inverter" section.

"Robert Obermayer" skrev i en meddelelse news: snipped-for-privacy@individual.net...

Thanx. I read a few older postings here on the same subject and tried the trick with an external 43V directly on C940 I disconnected Q9070 when I tried. Current limited to just 500mA.

R934 got VERY warm (the 51V zener is not shorted). I tried to lift R934 witch resulted in a burned 33ohm resister in series with CR948. Q946 or 947 died and have to be replaced.

Can I replace all the diodes on the secondary side with 1N5059 or 1N5062?

What substitute can I use for Q946+Q947?

Is it very important to use 840uF/12V caps or could I use a standard 640uf or 1000uf 16V?

Peter

"Peter Andersen" wrote in news:44c0cb56$0$84032$ snipped-for-privacy@dtext01.news.tele.dk:

You may have an out-of-spec zener or bad SCR;the SCR should not conduct and R934 should not either. That's an overvoltage crowbar circuit. Of course,they also sample the voltage across the power oscillator resistor R949(the number is blurry). Since the 33R (R948?)is burned,the SCR may be a problem.

replace both xstrs at the same time.This suply is similar to the one in

2213/15 and 2235 scopes. I believe the xstrs are TIP-31Cs.

the TEK p/n in 2215 manual is 151-0476-02

my 2215 manual says they're 200PIV,0.75A diodes TEK p/n 152-0414-00, Unitrode UTR308 they may be "fast-recovery" types.

TIP-31C

1000uf/16v would be fine if they physically fit. Use low-ESR 105degF types. (switcher-grade) ;regular electrolytics will not last long in this app.

--
Jim Yanik
jyanik
at
kua.net

Ok, I will take it out and test it.

I have a lot of TIP130 here - I think these could do it?

200PIV? Could the 1N400x (1A) be used here? I dont know what paramteret would characterize a diode as a fast-recovery type?

Thanx!

Peter

"Peter Andersen" wrote in news:44c10a9c$0$84015$ snipped-for-privacy@dtext01.news.tele.dk:

TIP-130?? IMO,that does not equal TIP-31C. Do they even have the same footprint? If the specs are similar,they could be used for test,but I'd want the right parts for normal operation.

I believe 1N40xx are ordinary diodes,not fast-recovery.

100ns or less recovery is what you want.

--
Jim Yanik
jyanik
at
kua.net

Ok, thanx. I have found some cheap 1N4935 that could be used, they are fast recovery and with the same pin-diameter as the old ones. BTW: in my scope there are black diodes and blue diodes on the secondary side - different type? could I still use the above?

There is a lot of small caps on the preregulator and inverter circuts. I think a lot of them is tantalium caps (?). Could I change them to another type? plastic? with the same value and footprint?

Yesterday I just realized that the EMI filter on this scope has been disconnected, is this normal? maybe this is why I have problem with the scope now. I have taken the TL594 out and want to test it separately.

--
Vh. Peter Andersen
www.mespilus.dk

"Peter Andersen" wrote in news:44c1e376$0$2108$ snipped-for-privacy@dtext02.news.tele.dk:

The diodes for the 30V and 100v suppplies are 400PIV,0.75A ratings;UTR307

No.That keeps switching noise from going back into the mains and radiating all over.

You can test the entire pre-regulator circuit (the 43VDC supply) if you can make a load to handle 43V at ~1 amp. Probably a 0.5A load would suffice.

I used six 430 ohm 7W WW resistors normally used in the vertical output stage of a 465,that's what I had in bench stock. It doesn't have to be ON for very long,just enough to check the output voltage.

--
Jim Yanik
jyanik
at
kua.net

What does PIV stands for? is it just the voltage rating?

I know - I was just thinking that there could be a good reason why someone has done that on the one I have. Maby not.. I have to test that filter and connect it properly again.

Do you totally disconnect the inverter when you are testing the prereg.?

--
Vh. Peter Andersen
www.mespilus.dk

"Peter Andersen" wrote in news:44c294d5$0$84022$ snipped-for-privacy@dtext01.news.tele.dk:

peak inverse voltage.

paralleled,I forgot to mention. (Used those nice TEK ceramic strips from the old 500 series,too bad they aren't made any more,they were handy for dummy loads.)

Yes. I'm just testing the pre-regulator,I don't want to power the whole scope. I've mostly used it on 2213/15s where the pre-reg was a separate PCB,where the 2230 series had the pre-reg integrated onto the main board.I don't recall what I did to isolate the pre-reg on those 2230 series.

--
Jim Yanik
jyanik
at
kua.net

I have now tracked it down to be a problem with the inverter.

When I lift VR943 and R945 I can get the scope up and running!! It must obtain some current thru the thermal shutdown board I think for this to work. !!

I have replaced VR943 and chanced Q944 to a TIP31C, ok? - I couldn't measure any CB diode) and Q938 and Q939 seems to be ok (could these be replaced with BC558 if necessary?)

What could be the problem??

Peter

Dunno, but I usually have to replace ALL those lousy silver electrolytic capacitors in the power supply area. They're often nearly open circuits and leaking black goo out the bottom.

"Ancient_Hacker" skrev i en meddelelse news: snipped-for-privacy@s13g2000cwa.googlegroups.com...

All ready done :-)

Peter

"Peter Andersen" wrote in news:44c75c18$0$84039$ snipped-for-privacy@dtext01.news.tele.dk:

lifting VR943 is going to cause Q939 to turn on,turning on Q944. I don't know why you lifted R945,perhaps you mean you lifted R943 the current source for VR943?

Q946,947 are the TIP31Cs. Q944 should be some small signal xstr.

i have no idea,not knowing about BC xstrs.

Perhaps a problem in the A18 thermal shutdown assy;lift CR950 to isolate it.

--
Jim Yanik
jyanik
at
kua.net

A few facts re the tek 222x scopes:

(1) Like most scopes, the vertical channel voltage 1/2/5 knobs often wear out or break more often than the other knobs.

(2) So there's a net shortage of these knobs. Sometimes you gain a few when you have to scrap a scope that's hopeless.

(3) Many of these scopes get a bit dusty, so one is inclined to go to them cleaning solutions and a toothbrush.

(4) This works just fine on Tek 4xx, 5xx, 6xx series scopes. On the

222x series though, don't ask me how I learned this, the little black numbers on the knob skirt are decals, held on with dried fairy tears I think. Just a hint of "Windex" sends the numbers comically drifting all over the place, then they fall off onto your workbench. No amount of cursing can coax them to reverse their journey. Don't ask me how I learned this.

I think the next 222x scope that crosses my path will get a Wheee! trip over the edge of the nearest tall building.

:-) Well, I have mine up and running now. Everything seems to be fine. My

2220 is in VERY good condition. Looks like never been used. It costs me 120$ for the scope include local shipping and 30$ new components for the PSU.

Now I have to learn to use the storage section of it. Is there any readout's of v/div and time/div on the crt like on 2230?

What is excatly the difference between 2220 and 2230 storage scopes? the PSU is the same, and if I leaf through the servicemanual for the 2230 it looks like 2220.

--
Vh. Peter Andersen
www.mespilus.dk

"Peter Andersen" wrote in news:44c7eac9$0$2103$ snipped-for-privacy@dtext02.news.tele.dk:

You never told us what the source of the problem was. :-(

BTW,here's a nice reference and parts source for you;

--
Jim Yanik
jyanik
at
kua.net

Well.... It seems to be impossible for me to get this scope up and running properly. Everything was working fine at last. I had the TIP31C's on the table on a heatsink with wires connected to the board.

When I soldered it back - it wont start-up! Hmmm!!, I removed it and connected it back to the wires again - then everything was fine. If I removed the black and white (5V) supply to the digital board it could start-up just fine.

Then I adjusted the -8,6V and replaced the 10uF caps back to a the originaly

100V version (from 63V) and soldered the TIP31C back on the board. Now the scope is powering up and I'm happy.

This was yesterday. Today when I wanted to put the whole thing together - the scope is not powering up, just clip-clip-clip-clip. With out the black and white connection to the digital board it works ok.

My theory: I have changed all the originally 820uF caps to new 1000uF low-esr. The start current in these could be too high for the preregulator and it shuts down. Is the solution to get some another caps. (would be quite difficult) or to mod something?

I hate this power supply!!

Thanx.

Peter

"Peter Andersen" wrote in news:44c9bb4b$0$84013$ snipped-for-privacy@dtext01.news.tele.dk:

Perhaps the digital board is drawing too much on the 5V line?

You did catch me post about the TIP31C being one of the two inverter xstrs,not it's controller xstr you mentioned....? And usually,one replaces BOTH inverter xstrs when one is blown(especially when using subs),because the 2nd one was overstressed and may fail in the future.

No,the change to 1000uf should not be a problem. FYI,the 2230 43V pre-reg current-limits at ~1.3A,normal is ~1A.

--
Jim Yanik
jyanik
at
kua.net