Author Topic: TEK 2445 (not A, not B) repair - U800, fan, etc.  (Read 10532 times)

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Offline SkimaskTopic starter

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TEK 2445 (not A, not B) repair - U800, fan, etc.
« on: May 21, 2016, 06:00:13 pm »
"Scored" a Tek 2445 off ebay.  That was the cheap part.  Pictures, video clips to come.  Pulling them off the card now.  USB2 sucks when you can't find the right USB3 cord.

Bought the Tek 2445 knowing it had problems.  Screen info only shows up on the right half of the screen.  When the Horizontal Position knob is turned left, everything bunches up in the middle and stops.  Turn it to the right, everything moves to the right like it should.  Hooking the probe up to the CAL output shows a trace.  Everything else seems to respond correctly.  A couple of the smaller knobs were broke when I got it, and I broke a few more taking the front panel off.  Add those to the shopping list.

Following the schematics, for the voltages at the U800...  The +Out and -Out from the U800 going to the horizontal deflection plates voltages pretty much match up to the voltages & waveforms in the service manual...sometimes.  When the Horizontal Position knob is turned more to towards the right, the waveforms (#61 & #62 around page ~245ish of the 2445 service manual) match up.  When the screen starts to collapse (eg. try to get something to display on the left half), the waveforms almost look like they fold back over themselves).  Power and system voltages are within spec, +87v, +/-15v, +5v, and whatever else is in there.  I went to the power subsystem schematic page and checked pretty much every voltage I could find on that page.

The fan is, for all practical purposes...shot.  Spins, but doesn't spin very fast.  The bearings seem to be shot as I can move the motor shaft in and out about 1mm or so.  Can get a replacement at Qservice Electronics for $35.  Debating whether or not to go with that, or modify the whole thing to fit a PC fan, or both.  Maybe put a couple of those really thin fans like they use on video cards in/around the U800 mounted to the outside of the case and tap off that +15Vunreg lead that feeds the main fan.

Looks like I'll want to swap out a few of the caps on the power boards.  No evidence of leakage, but the bottoms of a few of the larger electrolytics are blackened.  Just swap them out and be done with it.
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline SkimaskTopic starter

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #1 on: May 21, 2016, 06:27:57 pm »
Just grabbed a screen shot of the Tek's display.  Nothing displayed on the left half.  Everything that's supposed to be on the left half is kinda "bunched up" into a single vertical line around the middle, and the right half of the screen looks normal-ish.
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline FlyingHacker

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #2 on: May 22, 2016, 04:29:18 am »
I have one of those. Great scope.

I would start with the power supply. The low voltage power supply is known for capacitor failures, both electrolytics, and the yellow box line caps. Check all the voltages and the ripple. You will likely want to do a complete re-cap on the low voltage supply. The Tekscopes mailing list has a list of modern equivalent caps to use.

Once you get the power sorted out then start looking at any other faults.
« Last Edit: May 22, 2016, 06:06:21 am by FlyingHacker »
--73
 

Offline SkimaskTopic starter

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #3 on: May 22, 2016, 05:29:44 am »
Any thoughts on the fan swap?
Can get a 'new'/refurb replacement at Qservice for ~$35, probably a few other places online as well.  I've got this squirrel cage fan, 12V @ 1.1A.  Blows a fair amount of air.  Looks like it'll damn near bolt right up to the chassis.
(This one to be exact:  http://g01.a.alicdn.com/kf/HTB184xoIXXXXXXjXVXXq6xXFXXXh/AVC-F9733B12HP-12V-1-1A-97X97X33MM-server-cooling-fan.jpg_640x640.jpg )

Searching around for complete recap kits for now.  If that fails, I'll start over at Digikey and see what happens.

Any idea what is supposed to be plugged into J110, J118, and J119 on the main PCB?
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline FlyingHacker

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #4 on: May 23, 2016, 05:46:23 am »
My concern would be to make sure that fan has enough power. Not sure how much the power supply is designed to handle. Check the specs on the old fan.

It is really easy to break the collet when you remove the fan. I SuperGlued mine and it worked fine.
--73
 

Offline SkimaskTopic starter

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #5 on: May 23, 2016, 06:27:41 am »
The old fan is that stupid looking stock brushless fan, Siemens I think.  Looks a bit like the big ol' caps it sits next to.

When I say "a fair amount of air", what I mean by that is, with a 12v input, the proposed replacement fan draws a little over an amp, and easily blows around a stack of papers about a foot away from the outlet.
I'm 143% sure it'll push a lot more air than what that stock fan was moving.

Re-cap parts on order.  About 52 caps, plus a handful of diodes, resistors, etc. on order from Digikey, as well as replacement knobs from various other places.  All the caps are 105C parts or better, higher voltage ratings, tighter tolerances, etc.etc.  And only $80 for everything.

All in all, if this works out right, short of a proper calibration, I'll have a practically pristine 2445 in a couple weeks.  Roughly a total of $260 invested, along with a few hours of work.
Sure, a guy can get a digital 'scope for a couple hundred more that's got a buttload more bells and whistles, takes up 1/4 of the space, half as noisy, uses 1/10 the electricity...but where's the fun in that?
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline Orange

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #6 on: May 23, 2016, 08:22:50 am »
You wrote that all powersupply rails are OK. That means you have a problem with U800.

Before you do anything on this scope you better focus on this part. They are very difficult to find, and if you do find it, probably very expensive.
 

Offline grumpydoc

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #7 on: May 23, 2016, 08:41:40 am »
You wrote that all powersupply rails are OK. That means you have a problem with U800.

Before you do anything on this scope you better focus on this part. They are very difficult to find, and if you do find it, probably very expensive.
Could be U800 but that normally shows up as things drifting to the left.

Make sure both horizontal deflection plates are connected.
 

Offline SkimaskTopic starter

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #8 on: May 23, 2016, 11:32:48 am »
Checked the rails.
Already have a 'new' U800 installed.
Checked the plate connections before I tore it down, measured/compared voltages, etc.
Waiting anxiously on those new parts to come in.
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline Orange

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #9 on: May 23, 2016, 12:39:04 pm »
Checked the rails.
Already have a 'new' U800 installed.
Checked the plate connections before I tore it down, measured/compared voltages, etc.
Waiting anxiously on those new parts to come in.
And did the new U800 fix the problem ????
 

Offline grumpydoc

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #10 on: May 23, 2016, 01:05:27 pm »
Checked the rails.
Already have a 'new' U800 installed.
Checked the plate connections before I tore it down, measured/compared voltages, etc.
Waiting anxiously on those new parts to come in.
In that case start with the final X amplifier.

Do you have a 2nd 'scope?
 

Offline SkimaskTopic starter

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #11 on: May 23, 2016, 01:14:30 pm »
Ya, I recorded some video of what the problem was before I tore it down.  Don't have any time to get it edited and posted.  Got a 2245 and an SDS7102 as well.
The display bunched up in a vertical line about 1/4" to the right of center, almost as if the electrons were bunching up against a wall.  You could see where the display should have been vertically, it just wasn't spread out like it should've been.  If the horizontal position was turned to the right, the display would move to the right and look normal (using the built in cal test point for something to display).  Move it back towards the left and anything that was displayed would bunch up.
I've seen other videos of folks with roten U800's.  It similar-ish, but not the same.  In most of the videos I've seen, the display kinda rolls off in one direction or the other when the chip gets heated up.  Mine is just plain stuck.  Don't have any cold spray either to try out.
Doesnt really matter much now anyways since as I mentioned, I already swapped the U800 and I'm going g to recap it later this week when parts show up.
And I'll take another look at the schematics for that final X amp.  Hope it isn't one of those hybrids...
« Last Edit: May 23, 2016, 01:16:57 pm by Skimask »
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline siggi

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #12 on: May 23, 2016, 01:19:55 pm »
Any thoughts on the fan swap?
Can get a 'new'/refurb replacement at Qservice for ~$35, probably a few other places online as well.

The old squirrel cage fan is wonderful when it works. It's temperature controlled and under normal conditions it runs pretty slow and quiet - you'd be hard put to hear it in an otherwise totally quiet room.

I was able to recondition the fan motor in my 485 which uses the same gitup. The fan was in pretty rough shape in that there was a horrible rattle when I ran it. 
If you desolder the motor from the control board, you can get to an adjustment screw at the back of the motor. I pulled the screw all the way out and flushed the motor with IPA to get old gunky grease out. Soaking it, then blowing and drying it out is probably a good thing to do.
After drying it, I put a drop or two of synthetic motor oil in it, and it works like a charm now.
You can then tighten up the set screw a little bit to get rid of the slop, though I don't think a bit of slop is a problem.

Beware that before all of this I tried putting a drop of 3-in-1 in there, and the fan didn't like that at all.
 
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Offline tautech

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #13 on: May 23, 2016, 01:24:20 pm »
Any thoughts on the fan swap?
Can get a 'new'/refurb replacement at Qservice for ~$35, probably a few other places online as well.

The old squirrel cage fan is wonderful when it works. It's temperature controlled and under normal conditions it runs pretty slow and quiet - you'd be hard put to hear it in an otherwise totally quiet room.

I was able to recondition the fan motor in my 485 which uses the same gitup. The fan was in pretty rough shape in that there was a horrible rattle when I ran it. 
If you desolder the motor from the control board, you can get to an adjustment screw at the back of the motor. I pulled the screw all the way out and flushed the motor with IPA to get old gunky grease out. Soaking it, then blowing and drying it out is probably a good thing to do.
After drying it, I put a drop or two of synthetic motor oil in it, and it works like a charm now.
You can then tighten up the set screw a little bit to get rid of the slop, though I don't think a bit of slop is a problem.


Beware that before all of this I tried putting a drop of 3-in-1 in there, and the fan didn't like that at all.
That's a good trick to know, thanks for sharing.  :-+
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Offline SkimaskTopic starter

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #14 on: May 24, 2016, 03:20:42 am »
If you desolder the motor from the control board, you can get to an adjustment screw at the back of the motor.
That little 'slot' in the shaft that doesn't spin is actually a screw?
Huh...Gotta go have another look...
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline siggi

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #15 on: May 24, 2016, 11:09:49 am »
Matthew D'Asaro did a full rebuild of one of those http://www.antiqueradios.com/forums/viewtopic.php?f=8&t=235478 fan motors.


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Offline SkimaskTopic starter

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #16 on: May 24, 2016, 07:04:22 pm »
Matthew D'Asaro did a full rebuild of one of those http://www.antiqueradios.com/forums/viewtopic.php?f=8&t=235478 fan motors.
Had a look at the above page.  Ya, I'm not gonna play that game.
I've got a couple of squirrel cage fans of various sizes here that'll just about fit in that shrouded area in the back of the 'scope.  Maybe add a PCB with a regulator, filter caps, and a couple of ferrite beads along the wiring, and put it all in that little bowl where the original fan motor used to sit.

But for grins, I got the motor in the cleaner now, and I'll try the synth motor oil as described earlier.  Put 15v across the PCB and see what happens.
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline tautech

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #17 on: May 24, 2016, 09:31:08 pm »
Put 15v across the PCB and see what happens.
With a current limited PSU or a light bulb in series I hope.  :scared:
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Offline siggi

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #18 on: May 24, 2016, 11:55:47 pm »
Matthew D'Asaro did a full rebuild of one of those http://www.antiqueradios.com/forums/viewtopic.php?f=8&t=235478 fan motors.
Had a look at the above page.  Ya, I'm not gonna play that game.
Yeah - I wouldn't attempt that either, but at least you get great pics of the motor's construction :).

But for grins, I got the motor in the cleaner now, and I'll try the synth motor oil as described earlier.  Put 15v across the PCB and see what happens.
Good luck, I hope it works for you. I modded my 2465 with a 60mm case fan, but I hated the fan noise so much I eventually snagged a NOS fan motor on eBay and fixed'er back.
Now of course I mostly use the 2467 and a TDS784D - so much for a quiet lab :/.
 
My 485 fan with the impeller mounted on the bench consumed about 85mA, standalone on the bench after a drop of oil. Any interfering with the airflow dropped the current usage - putting my hand in front of the center of the impeller dropped it to ~65mA, so I suspect it runs at even lower currents in-place.
 

Offline SkimaskTopic starter

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #19 on: May 25, 2016, 04:12:13 am »
Well, I didn't take the motor apart completely, but I did remove that rear screw, and dunked the whole thing into my cheap ultrasonic cleaner for a half dozen 3 minute cycles.  Shook it up a bit, blew it dry, put a drop of Mobil 1 (should be good for 15,000 miles right? :D) , put the set screw back in and tightened it down until there wasn't any axial play in the main shaft, resoldered it to the circuit board (more on that later), and it worked just fine.  Wasn't noisy, was smooth, etc.

And I didn't just throw 15v across it.  I used my DP832 and ramped up the current slowly until I was sure it was dead shorted or anything...

8v @ 50mA
9v @ 53mA
10v @ 58mA
11v @ 61mA
12v @ 67mA
13v @ 74mA
14v @ 80mA
15v @ 89mA
16v @ 100mA
17v @ 112mA
18v @ 127mA
19v @ 149mA
20v @ 173mA

Schematic shows it being connected to the +15V-Unreg rail, but also shows a test point with 19.2V on it.

Hell with it.  I'll reinstalled the original part and keep an eye on it.
However, I am going to tap off that same +15V-Unreg rail and install something like a 50mm or 70mm on the bottom/outside of the case, blowing directly on the U800.  Maybe throw an inline 7805 or 7808 to keep the noise down a bit, if I have to, I'll run it off a separate supply.  Small hassle/price to pay to keep that U800 alive.
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline SkimaskTopic starter

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #20 on: May 26, 2016, 07:15:26 am »
New parts showed up.  ~40+ caps, a few resistors, etc.  Swapped them all out, and tested the pulled parts for grins.
1 250uF cap on the main input showed completely open, 2 other 100uF caps showed stupid high ESR, >50ohm.  Another 7 caps showed higher ESR's than their replacements by 1 or 2 orders of magnitude.
4 1N5821's on the input, pulled them for grins and replaced them.  3 of 4 of them were just a bit leaky, about 1K reverse leakage on 3 of them, 4th one was solid.  Replaced them all anyways.
All caps replaced with Nichicon or Panasonic, except for the film caps which were either KEMET or Vishay.  Most of the pulled parts were 85C, replaced with either 105C or 135C parts.  Also upped the voltage rating on all replacement caps by a step or two.
EXCEPT...the two big fat 290UF on the tray next to the cooling fan motor.  I got 2 new ones in...and the leads aren't long enough to reach from that tray down to the PCB.  WTF!!!
The old cap's are Sprague 290UF/200DC, measure out at ~290UF and < .1ohm ESR.
New ones are Nichicon 330UF/300DC @ 85C (couldn't find 105C parts), measure out at ~330UF and < .2ohm ESR.
Old ones aren't bulged, discolored, just a bit dusty and cleaned up with a douching of a bit of IPA.
I think I'm good to go.

Tomorrow's job will be to remember where all these nuts, bolts, washer, connectors go.  :-//
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline FlyingHacker

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #21 on: May 26, 2016, 03:41:07 pm »
Yeah, those bulk capacitors will require some extra wiring (with a decent gauge wire to handle the inrush). I ended up leaving my bulk caps alone. According to the guys on Tekscopes they rarely fail. If I had had the wire to hook them up at the time I would have replaced them when I had the instrument open, though.

Reminds me... I should open her up for an annual inspection  :-+
--73
 

Offline SkimaskTopic starter

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #22 on: May 26, 2016, 04:23:41 pm »
Gonna have look around later today.  I'll bet I've got some fairly big gauge pins that could easily get stuck in the holes, then stuff the cap wires into the pin where the wire should be.

I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline FlyingHacker

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #23 on: May 26, 2016, 05:02:17 pm »
My plan was to use some 20 or 22 gauge solid wire and run them up to the holder. Then pad the holder with something like foam, etc. It would be a good idea to have them insulated or heat shrunk, or both. I think some guy shows his on YouTube if you search for it.

Like I said, I bought the filter caps, but the ripple was fine so I just left them as they were.
--73
 

Offline SkimaskTopic starter

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Re: TEK 2445 (not A, not B) repair - U800, fan, etc.
« Reply #24 on: May 26, 2016, 10:09:07 pm »
Possibly overthinking this again...haven't put it back together yet...haven't had the time to do it yet...

Read above and you'll find the description of this 'scope's original problem...the display STOPS at about mid-screen, only shows up on the right side, if the horizontal position knob is turned, it stops at mid-screen, and the picture/data that is supposed to be on the left is basically bunched up in a line in the middle of the screen.

If one of the horizontal plates in the CRT was broken/disconnected/shot/etc, what would that do to the display on the CRT?  I guess the real question is, if one deflection plate is broke, would that cause the beam to only be deflected in the other direction?  Does a CRT require both deflection plates to move a beam, for instance one positive, one negative to go one direction, and vice-versa.  Or does a CRT only require voltage on one plate to move the beam in any particular plane?

Just attempting to wrap my head around how the horizontal beam deflection could hit such a hard-limit/brick-wall with a handful of rotten transistors and cap's as mine was showing...
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 


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