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TDS544A major surgery - CRT issues

Ed Breya
 

A few years back, I reported on restoring a TDS544A that had the capacitor plague on the acquisition board. That part worked out OK, but a couple months or so later, the HV transformer in the CRT circuit arced and was non-recoverable (way too much charcoal inside). Ever since, I have managed to keep using it though, with an external VGA display - nice and big, but awkward. At the last flea market of this season, a picked up a TDS540 carcass for cheap, figuring maybe I could swap out the displays and restore the 544A to full operation.

The 540 was just the guts with no can, but otherwise complete, and marked "won't start up" or something like that, so I figured typical PS trouble, and the display was likely OK. It turned out the PS and display were in fine shape, but the acquisition board indeed had the plague, so bad that it crashed the supply. I tried to clean it up as usual, but it did not recover enough. It all fires up, with a nice bright display, and passes the self-tests except for the dreaded acquisition failure.

I have decided to go ahead with the display swap, and let the 540 be for the spare parts dept, but thought I'd check here for any advice before starting. The main issue is that the 544A has the color-shutter, while the 540 is straight monochrome. Is the same CRT/display unit used in both? I vaguely recall seeing online somewhere that the shutter may be glued to the CRT - that would spoil the whole deal. Does anyone know if this is the case?

I'm up at the farm this weekend, so don't have access to all my usual tools and equipment, and I didn't think to bring all my notes and info from working on this before. The original shot display is still in the 544A (but unhooked), so I didn't even even experience removing it. I assume the front all has to come off, then the color-shutter and CRT out the front, and the rest out the middle after everything is opened up. If the shutter is bonded to the CRT, then the only other option is to leave the assembly in, and just replace the HV PS section - if it's compatible. Does anyone know if the CRTs are the same in this regard? I recall that before the 544A's display crapped out, the CRT seemed old and dim, so I'm hoping this new stuff will go right in. On the other hand, it's possible that the poor brightness on the old one was a symptom of the HV transformer going bad, so maybe it's in better shape than I thought.

Anyway, just thought I'd ask if anybody happens to know quick answers to these questions. I've got both units here, ready to start once I clear some usable space and gather up some tools. I'd like to wrap it up tonight, one way or another - tomorrow will be occupied with the water tank and other outdoor projects.

Ed

Harvey White
 

To the best of my knowledge. the displays are much the same, the difference being the LCD shutter feed from the MB.  From what I know, the LCD shutter is "fastened" to the display with an intermediate gel, and one problem is that the gel goes odd, perhaps dries out.  I know that there is at least one instance where the gel was rather laboriously scraped out, and the system was restored.  If the CRTs are identical, you may wish to just simply replace the display boards.

Not a quick answer, because I don't know (I have a 540 and a 640), wish I had a 544 or a 644 for just the color capability when running an external display, but that's the best I can do.

Harvey

On 10/19/2019 8:11 PM, Ed Breya via Groups.Io wrote:
A few years back, I reported on restoring a TDS544A that had the capacitor plague on the acquisition board. That part worked out OK, but a couple months or so later, the HV transformer in the CRT circuit arced and was non-recoverable (way too much charcoal inside). Ever since, I have managed to keep using it though, with an external VGA display - nice and big, but awkward. At the last flea market of this season, a picked up a TDS540 carcass for cheap, figuring maybe I could swap out the displays and restore the 544A to full operation.

The 540 was just the guts with no can, but otherwise complete, and marked "won't start up" or something like that, so I figured typical PS trouble, and the display was likely OK. It turned out the PS and display were in fine shape, but the acquisition board indeed had the plague, so bad that it crashed the supply. I tried to clean it up as usual, but it did not recover enough. It all fires up, with a nice bright display, and passes the self-tests except for the dreaded acquisition failure.

I have decided to go ahead with the display swap, and let the 540 be for the spare parts dept, but thought I'd check here for any advice before starting. The main issue is that the 544A has the color-shutter, while the 540 is straight monochrome. Is the same CRT/display unit used in both? I vaguely recall seeing online somewhere that the shutter may be glued to the CRT - that would spoil the whole deal. Does anyone know if this is the case?

I'm up at the farm this weekend, so don't have access to all my usual tools and equipment, and I didn't think to bring all my notes and info from working on this before. The original shot display is still in the 544A (but unhooked), so I didn't even even experience removing it. I assume the front all has to come off, then the color-shutter and CRT out the front, and the rest out the middle after everything is opened up. If the shutter is bonded to the CRT, then the only other option is to leave the assembly in, and just replace the HV PS section - if it's compatible. Does anyone know if the CRTs are the same in this regard? I recall that before the 544A's display crapped out, the CRT seemed old and dim, so I'm hoping this new stuff will go right in. On the other hand, it's possible that the poor brightness on the old one was a symptom of the HV transformer going bad, so maybe it's in better shape than I thought.

Anyway, just thought I'd ask if anybody happens to know quick answers to these questions. I've got both units here, ready to start once I clear some usable space and gather up some tools. I'd like to wrap it up tonight, one way or another - tomorrow will be occupied with the water tank and other outdoor projects.

Ed



Dan Fish
 

Ed,

I have a TDS584 that I purchased with the wrinkles in the gel between the CRT and shutter. I removed the gel, but the CRT was still dim and had blobs of pink and blue colors in the shutter. So I removed the CRT and shutter driver assemblies and put in an LCD display so that I can use the scope. So now I have the CRT and shutter driver assemblies that are probably good. If you are interested in trying them in your 544 you can have it for the cost of reimbursing me for the shipping charge. I am in WA state. You can contact me at defish1@....

Dan

@Arcticgeek
 

Ed,

The monochrome CRT used in the TDS540 is NOT the same CRT used in the color scopes such as the TDS544 and others. The HV requirement is different for both CRTs and the deflections yokes are different (and use different connectors). I've never actually tried substituting a B&W CRT for the color one, but my assumption is that it would be a spectacular display of smoke.

I have actually successfully removed a few of these color LCD shutters from dim CRTs, it can be done but you have to be careful not to cut the wires going around the display to LCD color shutter. The gel that was used in between the shutter and CRT was only used on the early models such as the TDS544A and TDS744A. It seems that newer units like the TDS644B/TDS654C and TDS754C/D did not have the gel, and that makes removal; a bit easier. If you have a good/bright CRT with a bad shutter you can swap a good shutter from a dim CRT. After the swap I simply bond the replacement color shutter to the CRT using RTV.

All of this is a bit of a pain but can be done.

Ed Breya
 

Thanks Dan, let's talk about it. I'm kind of busy right now but will try to figure out all the pieces and part numbers etc soon. The transplant was unsuccessful - the 540 display installed in the 544 just showed a bright blank raster. I think the reason is that the 544 display is nearly a VGA type, with higher scan rates, and somehow they did a converter from dot-sequential to field-sequential, to drive the color shutter. When I opened it up, the first thing I noticed was the yoke wound with Litz wire - definitely for higher scan rates than the 540 one, which looks closer to a regular NTSC video unit. It's probably somewhere in between. You can reach me at eb at telight.com.

Ed

Ed Breya
 

Oops. %$^& I hit the wrong button - this was supposed to be a private message. Please ignore. Ed