Author Topic: Tektronix TDS544A Repair  (Read 24642 times)

0 Members and 1 Guest are viewing this topic.

Offline PartialDischarge

  • Super Contributor
  • ***
  • Posts: 1611
  • Country: 00
Re: Tektronix TDS544A Repair
« Reply #25 on: September 28, 2016, 07:39:40 pm »
Felt like rescuing this thread instead of creating a new one.

Just got a TDS744A, works well overall. Haven't seen any leaking caps but will replace them nonetheless with 10/35V and 33/25V caps. A range of settings on
CH1 don't work well, 200mV to 1V show ground (but from time to time I hear the click from a relay and the signal goes through so it must be a contact thing)

Just ordered a DS1650Y and sockets... but my main question is, what about the other DS1486??? do I need to change/backup it?

 

Offline skennedyTopic starter

  • Contributor
  • Posts: 44
  • Country: au
Re: Tektronix TDS544A Repair
« Reply #26 on: September 28, 2016, 11:10:48 pm »
There was some discussions on the Tekscopes group on Yahoo regarding the relays wearing out. Might be a good spot to look. I think they diagnosed the issue by measuring the on resistance of the relays and more than a couple of ohms replaced them.

The TDS744A is quite a bit different from the TDS544A. Most of the capacitor issues that the earlier scopes had were resolved by the time the TDS744A came out.
 

Offline PartialDischarge

  • Super Contributor
  • ***
  • Posts: 1611
  • Country: 00
Re: Tektronix TDS544A Repair
« Reply #27 on: September 29, 2016, 06:18:58 pm »
There was some discussions on the Tekscopes group on Yahoo regarding the relays wearing out. Might be a good spot to look. I think they diagnosed the issue by measuring the on resistance of the relays and more than a couple of ohms replaced them.

The TDS744A is quite a bit different from the TDS544A. Most of the capacitor issues that the earlier scopes had were resolved by the time the TDS744A came out.

Yes, the caps don't seem to be a problem and the relay seems to be a contact issue.

However the Dallas rams worries me. I found a programmed that can read/write the RTC DS1486 and the DS1650Y so I'll desolder them and try that next.

 

Offline cncjerry

  • Supporter
  • ****
  • Posts: 1269
Re: Tektronix TDS544A Repair
« Reply #28 on: October 02, 2016, 02:17:47 am »
It's unlikely the caps are wholesale bad in a 744 like the 5xx series.  I wouldn't get carried away unless you find one through troubleshooting to be defective.
 

Offline nctnico

  • Super Contributor
  • ***
  • Posts: 26755
  • Country: nl
    • NCT Developments
Re: Tektronix TDS544A Repair
« Reply #29 on: October 02, 2016, 02:33:08 am »
AFAIK the capacitors are only bad in the scopes from the early 90's (say 90 - 92). I had a TDS510A from 1995 and the capacitors didn't leak at all.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline PartialDischarge

  • Super Contributor
  • ***
  • Posts: 1611
  • Country: 00
Re: Tektronix TDS544A Repair
« Reply #30 on: October 09, 2016, 09:39:24 am »
The caps seem to be fine, so I left them.

The attenuator problem is solved too. Seemed to be a contact problem although it took me a couple of tries to fix it. I did clean the contacts with
alcohol and most importantly I did pinch with tweezers the spongy gold contacts that interconnect the boards as some seemed to be too compressed.

I had another issue, in which the signals from 30Mhz and up did not trigger properly, there was jitter in the signal. After chasing a phantom hw problem, eventually it solved with the SPC self calibration.

Both NVR are backed up too

Now I can enjoy the scope!
« Last Edit: October 09, 2016, 10:02:18 am by MasterTech »
 

Offline ruairi

  • Frequent Contributor
  • **
  • Posts: 302
  • Country: us
Re: Tektronix TDS544A Repair
« Reply #31 on: February 08, 2017, 07:13:14 am »
Hi all,

I figured it's best to keep TDS series issues in one thread.  I have a very clean TDS620A that I bought from a friend a few years back, cal 'd in 2012 and has worked beautifully until tonight. 

I was probing around on an opamp stage when I accidentally touched the probe off of the palm of my hand, whether coincidence or not the scope flashed onscreen and shutdown. It attempted to reboot but failed every time.

I learned about the infamous electrolytic cap issues after I bought this scope so I opened it expecting the worst. Even under the magnifier I cannot see a single leaky cap or corroded trace on the board, everything is super clean.  I spot checked the ESR on maybe 10 caps with my Peak Atlas and every cap was sub 1 ohm.

Is there something obvious that I'm missing?  Any ideas appreciated.

Cheers,
Ruairi

 

Offline daveyk

  • Frequent Contributor
  • **
  • Posts: 413
  • Country: us
Re: Tektronix TDS544A Repair
« Reply #32 on: April 22, 2017, 03:23:48 am »
If that is really the fault, then I'm really looking forward to this repair. I skip these kind of early DSO when browsing though eBay. There's too much that can go wrong. Failed EPROMs, dying CRT, damaged ASICs. Just look at Dave trying to fix that LeCroy oscilloscope.

Or sometimes you get lucky and just have to replace caps.
On the Tektronix TDS500, 600 and 700 series you can't go wrong unless the display is bad. I have restored several. The problems with the leaking capacitors are well known and fixable. This scope doesn't seem to have a startup failure so chances are the capacitors didn't do any real damage yet. If you want to be safe its better to buy a scope from these series made after 1994.

There are 10uf and 33uf caps on the CPU, acquisition, front panel and I/O boards. What I do first is wash the board with a strong cleaner (like 'simple green' or 'st marc' paint cleaner. Look 'm up with Google and find something with the same ingredients) and a tooth-brush. Rinse with water and then clean with alcohol or ethanol. Then rinse with water and let it dry on a heater.

When removing the caps I mark the similar values first, remove the capacitors, place new ones and then do the same for the other value. Most capacitors are mounted in the same direction but some are reversed so look at the '+' signs on the boards.

While the boards are drying its a good time to clean the front panel, knobs, rubber key mats and housing. It will make you scope look like new. This is TDS544A I restored a couple of months ago (it had a bad CRT driver board and some problems caused by leaking capacitors but nothing that couldn't be fixed):

I have one that fail acquisition during boot up. A lot of the caps were leaking on the acq board but not all. So far I have replaced about 75% of the caps on the acq board and am finished for the night. I tried booting before bed and I get same error. The ones I didn't change yet aren't leaking. There is some corrosion but not a huge amount.  I don't hold out a lot of hope that changing the remain caps on that bottom acq board will fix it.

It's a shame the crt is bright and the colors nice.

It might end up on the scrap heap.

Dave


Sent from my iPhone using Tapatalk
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf