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TDS544A status


Ed Breya
 

Have replaced all the bad Al electrolytics with solid Ta caps on the controller, front panel, and printer port boards, and the instrument has survived so far, including board washing. Next will be the acquisition board - only about 90 or so more of those stupid caps to go.


Ed


Ed Breya
 

I let it run all night for burn-in testing. It was just fine first thing this morning, then a little later I noticed no display and that smell of a burnt part. I thought one the replacement caps failed, but it looks like something in the display unit went out instead. Running it with external VGA, it said POST was OK and ran as usual, so I'll have to dig into the display next.


Ed


Ed Breya
 

Oh well, this one's a goner as far as being a stand-alone scope goes. The burnt part is the HV flyback transformer T120. Upon opening it up it was obvious there was a charcoal patch on the top where it was arcing. It looks like it had internal failure, then burned up enough to also arc to the core. To confirm, I propped it open enough to observe, and rigged up enough connections on the control board to provide power to the display. It immediately lit up on power-up, and looked like a miniature charcoal BBQ glowing away. This transformer may have been on its way out for a while. As I reported at the very beginning, the display was quite dim, but I cranked up the internal intensity and contrast tweaks to get a decent display. This one extra night of continuous running was probably enough to finish it off - I never ran it so long before.


At least it was easy to find the problem. It's not worth fooling around with any more, so I'll set it aside - the CRT and shutter can be saved as spares for the 754A, and if I ever need it as a scope it can still work with an external VGA display, like in a dedicated rack mount setup. If I happen to find a junker for cheap that's ruined because of the bad caps, but has a good display, that may work out too, but not worth worrying about now. Even so, it still needs all those bad caps replaced on the acquisition board. I may just strip them all off and wash the board to prevent further damage, and set it aside for future consideration.


Ed


stefan_trethan
 

Best to consider yourself lucky that the burn-in did not turn into a
burn-down during the night.
The CRT on my TDS544A isn't very bright either, especially if you work
all 4 traces you can hardly see some colours.
The best repair would be to fit an LCD screen, but not very cheap.

Definitely take those caps off and wash the ACQ board. If nothing else
you can make someone happy in the future.



As an aside, it is a bad idea to run a board with electrolyte leakage
at all. Electrochemical corrosion makes the problem worse.

ST

On Thu, Jan 21, 2016 at 7:28 PM, edbreya@... [TekScopes]
<TekScopes@...> wrote:
Oh well, this one's a goner as far as being a stand-alone scope goes. The burnt part is the HV flyback transformer T120. Upon opening it up it was obvious there was a charcoal patch on the top where it was arcing. It looks like it had internal failure, then burned up enough to also arc to the core. To confirm, I propped it open enough to observe, and rigged up enough connections on the control board to provide power to the display. It immediately lit up on power-up, and looked like a miniature charcoal BBQ glowing away. This transformer may have been on its way out for a while. As I reported at the very beginning, the display was quite dim, but I cranked up the internal intensity and contrast tweaks to get a decent display. This one extra night of continuous running was probably enough to finish it off - I never ran it so long before.


At least it was easy to find the problem. It's not worth fooling around with any more, so I'll set it aside - the CRT and shutter can be saved as spares for the 754A, and if I ever need it as a scope it can still work with an external VGA display, like in a dedicated rack mount setup. If I happen to find a junker for cheap that's ruined because of the bad caps, but has a good display, that may work out too, but not worth worrying about now. Even so, it still needs all those bad caps replaced on the acquisition board. I may just strip them all off and wash the board to prevent further damage, and set it aside for future consideration.


Ed






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Ed Breya
 

The old caps are gone, the board's washed, and it's all back together except the display is disconnected. I have it running now for another burn-in to dry out any residual moisture. BTW it seems to run fine without any electrolytic bypass caps on the acquisition board - the ceramic ones all over the place should take care of fast stuff, but there could be slower stuff and supply ripple that may cause various issues under some conditions. If I re-commission this scope, I'll put in the Ta replacements.


I counted the husks after ripping them all out - 68 of those caps were on there. My previous mention of 90-something must have been the total estimate for the whole scope, so not as many left to replace as I thought - yippee.


Ed


bddicch
 

hi Ed please send me an email I have the same unit TDS544A and calibration software. now I can buy a TDS754D processor fail. send me email please: c.dickens@...


please email me.
greetz charly


Ed Breya
 

I'm not sure what you mean:


"hi Ed please send me an email I have the same unit TDS544A and calibration software. now I can buy a TDS754D processor fail. send me email please: c.dickens@... mailto:c.dickens@...


please email me.
greetz charly "



I can't send emails directly to anyone in the group because the address is blanked. I think you can email to me at my user name at yahoo.com.


Ed


stefan_trethan
 

Charly is c.dickens@...
or if yahoo tries to mess with it again:

c.dickens at xs4all.nl

ST

On Thu, Jan 21, 2016 at 11:34 PM, edbreya@... [TekScopes]
<TekScopes@...> wrote:
I'm not sure what you mean:


"hi Ed please send me an email I have the same unit TDS544A and calibration software. now I can buy a TDS754D processor fail. send me email please: c.dickens@... mailto:c.dickens@...


please email me.
greetz charly "



I can't send emails directly to anyone in the group because the address is blanked. I think you can email to me at my user name at yahoo.com.


Ed








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Ed Breya
 

OK - message sent.


Ed Breya
 

Now I'm getting paranoid - I just remembered that lately the 754A display sometimes has slight flickering in the display shortly after power-up, and then would be OK after warming up a bit. I hope this is not a sign of impending doom like a flaw in the HV transformer that gets worse as happened in the 544A. I'm thinking about maybe opening it up to see if there's any evidence of HV leakage on the outside of the transformer.


Ed


stefan_trethan
 

It can never hurt to open it up and have a look.
Except in those cases where you damage something in the process of course. ;-)

Even if there is nothing to be found at the very least it will give
you some idea what to expect when things do go wrong.

ST


On Fri, Jan 22, 2016 at 5:04 AM, edbreya@... [TekScopes]
<TekScopes@...> wrote:
Now I'm getting paranoid - I just remembered that lately the 754A display sometimes has slight flickering in the display shortly after power-up, and then would be OK after warming up a bit. I hope this is not a sign of impending doom like a flaw in the HV transformer that gets worse as happened in the 544A. I'm thinking about maybe opening it up to see if there's any evidence of HV leakage on the outside of the transformer.


Ed



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Hi Ed,

I have a number of those HV assemblies lying around from doing conversions to LCDs
They were converted as the CRTs were too dim for resale. I've been slowly unloading them on Ebay, but they're not hot sellers by any means. You can see one of them in Ebay item 321799417496
http://www.ebay.com/itm/Tektronix-TDS784C-HV-CRT-board-for-TDS700-600-and-500-series-oscilloscopes-/321799417496?ssPageName=STRK:MESE:IT http://www.ebay.com/itm/Tektronix-TDS784C-HV-CRT-board-for-TDS700-600-and-500-series-oscilloscopes-/321799417496?ssPageName=STRK:MESE:IT
If you're in the US, I'll send one to you for $75 including shipping.

Jay


Siggi
 

My TDS784D does this as well. I recapped the CRT driver board, which
alleviated this for a spell. I was in email contact with another TDS owner
who found that in his case it was due to degradation of the connections to
the horizontal deflection coil. Apparently there's reasonable peak currents
there and the connector is not so hot.
Once I get through the pile of HP gear hogging my bench ATM, I'll give the
connections a look-see and a good clean, as this random, flickering
shearing is a little annoying.

On Thu, Jan 21, 2016 at 23:04 edbreya@... [TekScopes] <
TekScopes@...> wrote:



Now I'm getting paranoid - I just remembered that lately the 754A display
sometimes has slight flickering in the display shortly after power-up, and
then would be OK after warming up a bit. I hope this is not a sign of
impending doom like a flaw in the HV transformer that gets worse as
happened in the 544A. I'm thinking about maybe opening it up to see if
there's any evidence of HV leakage on the outside of the transformer.



Ed






Ed Breya
 

Thanks Jay,
It's good to know these are available, but I'd be reluctant to get a new HVPS since the CRT isn't too good anyway. I can't look at it anymore now, but I recall that when it went through all the weird patterns at POST, there was one that lit the whole screen, and it clearly has some phosphor burn of various lines where the traces sat for long times.


I'd be more inclined to go with an LCD panel upgrade, but it probably isn't worth it on this scope. On the 754A it probably would be, if its display craps out.


Ed


 

Hi Ed,
Understod. Anyway, the LCDs I use is about $75 and I get 'em from China (Ebay). It takes a bit of shlocking, but the price is right.

Jay


Ed Breya
 

I managed to get a pretty good setup going. I happened to have an old rack-mount, slide-out LCD VGA station on hand that I got for free a while back. When opened up, it perches perfectly on top of the 544A. The native 640x480 VGA is also a perfect fit and gives a nice big-screen scope look that can be seen from across the room. It's a little awkward working the menu buttons since the display isn't physically associated with the button locations, but I can get used to it. The built-in laptop style keyboard isn't needed of course, but the deck makes a nice tray for paperwork or small items.

Ed