Author Topic: TEKHIND 2235 (Tektronix India)  (Read 3991 times)

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Offline abhi1981Topic starter

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TEKHIND 2235 (Tektronix India)
« on: July 05, 2023, 07:12:01 pm »
Hello,
Just got a  :-BROKE DEAD (Tekhind) Tektronix 2235 scope.
Nothing happens when I plug it in. The power led doesn't light up.
No visible damage other than some burnt rosin.
Where do I start?? :-// Please help.
Fuse is OK.



« Last Edit: July 06, 2023, 07:26:50 am by abhi1981 »
 

Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #1 on: July 06, 2023, 07:08:52 pm »


Cap C902 is blown. Most probably this is the culprit.
 

Offline Per Hansson

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Re: TEKHIND 2235 (Tektronix India)
« Reply #2 on: July 06, 2023, 07:41:28 pm »
Cap C902 is blown. Most probably this is the culprit.
That's just for line filtering, it will not have any effect, just make sure there is continuity through that board and it will be fine if you remove those two Rifa caps for now.
I would be allot more worried about the state of the main PCB, it looks like it was stored improperly and something leaked and corroded it?



 
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Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #3 on: July 06, 2023, 07:58:53 pm »
Thanks for your help Hansson. I'll remove the caps for the time being. Should they be replaced with exactly the same type of film cap or other material cap can be used ? Replacement options are limited in India.
Not much damage under the high voltage cover. But there is a lot of corrosion around U555. The traces have become discolored. I pretty sure someone has done resoldering with low quality flux paste, hence the burnt flux everywhere. I'll resolder all the corroded points.
« Last Edit: July 06, 2023, 08:07:33 pm by abhi1981 »
 

Offline Dave Wise

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Re: TEKHIND 2235 (Tektronix India)
« Reply #4 on: July 07, 2023, 01:45:18 pm »
You should join the "tekscopes" mailing list at groups.io, all the experts are there.
 
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Offline Per Hansson

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Re: TEKHIND 2235 (Tektronix India)
« Reply #5 on: July 08, 2023, 03:33:03 pm »
Thanks for your help Hansson. I'll remove the caps for the time being. Should they be replaced with exactly the same type of film cap or other material cap can be used ? Replacement options are limited in India.
They don't have to be exactly the same but they need to be class Y safety rated because they go from live and neutral to ground (chassis) so a short there would make the chassis live at mains voltage (Y class caps are guaranteed to fail open, not shorted).
P.S: You should replace all "Rifa" brand capacitors in the unit if one has failed the others are soon to follow...

Not much damage under the high voltage cover. But there is a lot of corrosion around U555. The traces have become discolored. I pretty sure someone has done resoldering with low quality flux paste, hence the burnt flux everywhere. I'll resolder all the corroded points.
I don't really agree, look at the first photo you attached around the screw hole in the PCB: there is corrosion underneath the soldermask.
That is something that usually only happens when a battery leaks, but there is no battery in the unit which is why I said something must have contaminated it.
Otherwise I don't know how this could happen...
Anyway trouble-shooting is straightforward if it is complete dead: just download the service manual and follow the mains input.
The failure could for example be C904 having failed shorted (it is another Rifa cap).
« Last Edit: July 08, 2023, 03:43:04 pm by Per Hansson »
 
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Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #6 on: July 08, 2023, 04:14:20 pm »
There is indeed corrosion under the solder mask, and I tried resoldering some of the corroded solder, but they are not melting easily due to the oxidation.

The voltage upto the power switch is 220V, but at the junction of diodes CR903 and CR901 its falling to 118V. Are the diodes faulty?
Checked them with DMM on diode mode, and they testing OK.
« Last Edit: July 08, 2023, 04:19:29 pm by abhi1981 »
 

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Re: TEKHIND 2235 (Tektronix India)
« Reply #7 on: July 08, 2023, 05:38:19 pm »
Someone may have used acid-flux to do a repair?

The corrosion damage looks pretty extensive, I'd be inclined to scratch the solder mask back wherever it's damaged and give it a really good clean to get any of whatever damaged it washed away. A fiberglass brush can help polish the traces clean too.
Then repair the traces by tinning with solder and/or soldering bare tinned copper wire along the traces if any are open circuit. Use lots of rosin flux to help the solder flow properly.
Seal it up again with conformal coating when you are finished and hopefully it will be ok..

If you leave it, the corrosion will probably just continue to get worse..
Where does all this test equipment keep coming from?!?

https://www.youtube.com/NearFarMedia/
 
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Offline Per Hansson

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Re: TEKHIND 2235 (Tektronix India)
« Reply #8 on: July 08, 2023, 05:53:06 pm »
The voltage upto the power switch is 220V, but at the junction of diodes CR903 and CR901 its falling to 118V. Are the diodes faulty?
Checked them with DMM on diode mode, and they testing OK.
Sounds like you are maybe measuring over only one of the diode pairs, measure the DC voltage on the large filter capacitor C906 instead, should be around 310VDC.
 
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Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #9 on: July 08, 2023, 06:05:42 pm »
Just switched on the scope to test voltage across C906, and behold, the scope suddenly powered on. The power led was on, but no trace. Beam find showed a bright dot. There was a faint whining sound and then there was pop. I switched it off immediately. No magic smoke but something definitely popped. I'll check further what blew up.
 

Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #10 on: July 08, 2023, 06:12:17 pm »
Someone may have used acid-flux to do a repair?

The corrosion damage looks pretty extensive, I'd be inclined to scratch the solder mask back wherever it's damaged and give it a really good clean to get any of whatever damaged it washed away. A fiberglass brush can help polish the traces clean too.
Then repair the traces by tinning with solder and/or soldering bare tinned copper wire along the traces if any are open circuit. Use lots of rosin flux to help the solder flow properly.
Seal it up again with conformal coating when you are finished and hopefully it will be ok..

If you leave it, the corrosion will probably just continue to get worse..

Totally agree with you. "Technicians" here still use paste flux, which leaves a burnt residue and they don't care to clean it  >:(
I'll clean the corrosion damage, but first it needs to power on properly.
 

Offline floobydust

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Re: TEKHIND 2235 (Tektronix India)
« Reply #11 on: July 08, 2023, 06:14:32 pm »
Spreadsheet list of 2235 capacitors to replace when doing a recap:  https://www.eevblog.com/forum/repair/tektronix-an-usm-4882235-high-8-6-v-ripple/msg2539461/#msg2539461
At this age, I replace all electrolytics in the PSU to prevent drama.
 
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Online tunk

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Re: TEKHIND 2235 (Tektronix India)
« Reply #12 on: July 08, 2023, 06:17:09 pm »
Ian Scott Johnston recently looked at a 2215 where he replaced 3-4 of
the Rifa caps. Your scope looks similar, maybe it has more of those caps.
https://youtu.be/MW_p8HzVAlY
 
 
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Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #13 on: July 08, 2023, 06:42:21 pm »
Can the Rifas be replaced with ceramic caps?
 

Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #14 on: July 08, 2023, 06:48:59 pm »
Or these
 

Online tunk

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Re: TEKHIND 2235 (Tektronix India)
« Reply #15 on: July 08, 2023, 07:08:16 pm »
I think they are safety caps (X or Y) and should be replaced with the same type.
 
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Re: TEKHIND 2235 (Tektronix India)
« Reply #16 on: July 09, 2023, 01:26:12 pm »
Yeah, only replace with the appropriate X or Y rated caps!

Also, here's a video I made on restoring and upgrading my 2235. There are some mods to the PSU section to make it more reliable.
https://youtu.be/lrXCVg6T-ek

Also, you may find some of your problems are due to the corrosion eating away traces, I'd start by scraping back the soldermask to check, or at least do continuity tests on all the corroded traces to be sure that none are open circuit...
Where does all this test equipment keep coming from?!?

https://www.youtube.com/NearFarMedia/
 
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Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #17 on: July 09, 2023, 02:57:41 pm »
Yeah, only replace with the appropriate X or Y rated caps!

Also, here's a video I made on restoring and upgrading my 2235. There are some mods to the PSU section to make it more reliable.
https://youtu.be/lrXCVg6T-ek

Also, you may find some of your problems are due to the corrosion eating away traces, I'd start by scraping back the soldermask to check, or at least do continuity tests on all the corroded traces to be sure that none are open circuit...

I was watching your video yesterday. Very good video.

The main problem in India is procuring the parts. You easily ordered all the parts from Digikey, but I cannot do so here. The postal system is very bad, packages from ebay etc. frequently get lost in transit. Only reliable service is Amazon, but not many electronic parts in stock.
I checked some local websites, but none of them have Y rated caps. X rated are available and at ridiculous prices.
Ceramic and mylar ones are easily available. Electrolytics are available, but not good brands such as Nichicon or Rubycon.

Regarding the corrosion, I'm also starting to think that the problem is not the caps but corrosion. There may be a loose connection somewhere, that is making intermittent contact. That's why the scope  suddenly powered on yesterday. I'll scrape the traces clean, resolder and then seal them with green UV mask.
 

Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #18 on: July 09, 2023, 02:58:57 pm »
Spreadsheet list of 2235 capacitors to replace when doing a recap:  https://www.eevblog.com/forum/repair/tektronix-an-usm-4882235-high-8-6-v-ripple/msg2539461/#msg2539461
At this age, I replace all electrolytics in the PSU to prevent drama.

Thanks. The spreadsheet was really helpful.
 

Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #19 on: July 09, 2023, 02:59:49 pm »
Ian Scott Johnston recently looked at a 2215 where he replaced 3-4 of
the Rifa caps. Your scope looks similar, maybe it has more of those caps.
https://youtu.be/MW_p8HzVAlY
 

Watched the video. Very informative.
 

Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #20 on: July 09, 2023, 07:28:57 pm »
Resoldered all the dirty points. Now the scope powers on. No trace. Beam find shows a bright dot.
The focus, position and intensity seem to work.
Checked the voltages on points W961, W968, W960, W954 and W956 - all OK.
Nothing has been changed on the board. One Rifa C902 is removed.
« Last Edit: July 09, 2023, 07:31:35 pm by abhi1981 »
 

Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #21 on: July 09, 2023, 08:33:32 pm »
IT'S ALIVE ;D ;D

My bad. The scope settings were wrong. Just followed the instructions on this post https://www.eevblog.com/forum/repair/tektronix-2235-no-trace/  and it works.
Channel B is noisy though.

But, how it started working suddenly is till a mystery. :-// :-//

Now to change those rifas.
« Last Edit: July 09, 2023, 08:37:44 pm by abhi1981 »
 
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Re: TEKHIND 2235 (Tektronix India)
« Reply #22 on: July 10, 2023, 01:20:47 am »
For the cost of shipping, I can see what I have in my stock of parts and send them over. A small box from Japan to India shouldn't cost too much.
Where does all this test equipment keep coming from?!?

https://www.youtube.com/NearFarMedia/
 
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Offline abhi1981Topic starter

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Re: TEKHIND 2235 (Tektronix India)
« Reply #23 on: July 10, 2023, 02:20:43 am »
For the cost of shipping, I can see what I have in my stock of parts and send them over. A small box from Japan to India shouldn't cost too much.
That's very kind of you Terra, but please don't send anything. The international postal services is very bad here. The package will surely be lost in transit.

Regarding the replacement for the rifas, should the capacitance be exactly the same or a higher value can be used.
 

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Re: TEKHIND 2235 (Tektronix India)
« Reply #24 on: July 10, 2023, 11:11:57 am »
It should be as close to original as possible, but a slight variation in capacitance wouldn't be terrible.
More important is that you don't use a lower voltage rating, but higher is fine (and potentially better for longer life).
Where does all this test equipment keep coming from?!?

https://www.youtube.com/NearFarMedia/
 
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