Tektronix model 2220 power supply problem ...

[Peter Andersen]

Hi
I have recently purchased a Tektronix 2220 digital storage scope in a very
good condition. Except the power supply!

The power supply is clicking normally due to some kind of overload. I have
repaired a lot of more "normal" smps's and I have lifted the diodes on the
secondary side and located the fault on that way.

But in this case I have unmounted everything on the secondary side, and the
problem persist! I found a service manual for a Tektronix 2230 and the PSU
seems to be the same. I have extracted a jpeg of the PSU here:

http://www.mespilus.dk/Tex_2230_smps.jpg

Can anyone please help me? I have never seen this kind of PSU design before.
It must be some king of capacitor problem or....?? can I be sure the problem
is on the primary side?

 

[Robert Obermayer]

The power supply is clicking normally due to some kind of overload. I have
repaired a lot of more "normal" smps's and I have lifted the diodes on the
secondary side and located the fault on that way.

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.

 

[Peter Andersen]

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).

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

 

[Jim Yanik]

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).

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.

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.

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

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

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

What substitute can I use for Q946+Q947?
TIP-31C


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

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.

 

[Peter Andersen]

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.

Ok, I will take it out and test it.

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.

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

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

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

Thanx!

Peter

 

[Jim Yanik]

Ok, I will take it out and test it.

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

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.

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

Thanx!

Peter

I believe 1N40xx are ordinary diodes,not fast-recovery.
100ns or less recovery is what you want.

 

[Peter Andersen]

I believe 1N40xx are ordinary diodes,not fast-recovery.
100ns or less recovery is what you want.

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.

 

[Jim Yanik]

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?

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

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?

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

maybe this is why I have problem with
the scope now. I have taken the TL594 out and want to test it
separately.

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.

 

[Peter Andersen]

Ok, thanx. I have found some cheap 1N4935 that could be used, they

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

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

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

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.

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.

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

 

[Jim Yanik]

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

peak inverse voltage.

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.

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.)

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

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.

 

[Peter Andersen]

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

 

[Ancient_Hacker]

What could be the problem??

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.

 

[Peter Andersen]

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.

All ready done

Peter

 

[Jim Yanik]

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. !!

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?

I have replaced VR943 and chanced Q944 to a TIP31C, ok?

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

- I couldn't
measure any CB diode) and Q938 and Q939 seems to be ok (could these be
replaced with BC558 if necessary?)

i have no idea,not knowing about BC xstrs.

What could be the problem??

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

 

[Ancient_Hacker]

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.

 

[Peter Andersen]

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.

 

[Jim Yanik]

Well, I have mine up and running now. Everything seems to be fine.

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

BTW,here's a nice reference and parts source for you;
http://www.sphere.bc.ca/test/tekequiv.html

 

[Peter Andersen]

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

BTW,here's a nice reference and parts source for you;
http://www.sphere.bc.ca/test/tekequiv.html

Thanx.

Peter

 

[Jim Yanik]

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.

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

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.

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.

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.

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