Re: Tek 576 Curve Tracer USB port to a cpu ... ?


Eric
 

This was along the lines I was thinking, having the video out VGA would let you use any older computer monitor. It would also let us view on a 19 inch or larger screen. The “zoom” in the larger screen would jump up the measurement ability of the unit from just having the larger display. I do like the ability to digitize and store 2 waveforms so that you could overlay the 2 for transistor matching. Replacing the tube seems to me will correct the 2 main terminal issues of the 576 The HV crapping out and the tubes being week.

On 1/8/2020 3:19 PM, Ed Breya via Groups.Io wrote:
Regarding converting the old 570 series CTs for "modern" display, readout, and control, there are degrees of complexity involved, ranging from fairly simple, like providing XYZ output in a unit with CRT or HV beyond hope, to very elaborate changes to full-blown, digital display and programmable functions. I'd recommend against getting too carried away with fancy modernization of these old beauties - it's doable, with a lot of effort, but not very practical. The most common, serious issue is the need to restore operation and usability to a unit with failed display. This can be done with internal modifications to provide XYZ access, to at least put the display on an external XY scope or monitor, or possibly digitize the signals and put in an LCD display, fitted to replace the CRT face inside. Providing readout of the myriad function settings adds quite a bit of complexity. Adding remote control borders on ridiculous. Again, all of this is doable, but not advisable. If you want all that, it's best to start from scratch and build or acquire appropriate SMUs and make a fully programmable system. The ATE industry figured this all out a long time ago.

I can speak readily to the 576 issues since I'm familiar with it. The biggest issue is CRT display failure, due to HV problems, or CRT wearout. As we can see from recent discussions, HV problems can be addressed with rewound transformers or even new designs. CRTs going bad have some chance of extra usable life by rejuvenation, but ultimately they will deteriorate beyond hope. There is no direct replacement for the 576 CRT except for the existing ones that may occasionally show up NOS, or salvaged from junkers. Once your CRT goes, that's it, and finding a replacement becomes ever more difficult over time.

What would be nice is the availability of a modern, LCD replacement, like those made for certain HP gear like the 8566/85660, which suffers the same sort of problem with CRT life. In this case, the XYZ info is readily accessible, and it's already digital, so interfacing is fairly straightforward. This is not the case with the 576.

I think the most essential, and simple "upgrade" for the 576 is to provide the same display info on a fitted LCD, as on the original CRT. The trick would be in digitizing and processing the XYZ info, and presenting VGA or whatever form is appropriate for the LCD. Getting the XYZ and other info from the 576 is fairly straightforward, but of course needs some internal modifications.

So, for anyone contemplating designing and selling a 576 "upgrade," the most important thing is to replicate the original XY display in real time, as would be shown on the CRT, while ideally also storing enough info to eliminate the flicker that results from multiple stepped-curve displays. Properly handling multiple curves may be the trickiest part. Other bells and whistles can be useful, but are secondary. Assuming the basic display can be made, the next most useful function I can picture, offhand, would be to replace the graticule intensity pot (no longer needed) with a button or rotary switch to activate digital storage features - imagine storing a curve of one device, compared to another that's live (or also stored), and so on.

I looked a bit at the 576 circuits, and it appears easy to get the XYZ info, especially if the CRT is eliminated. Unfortunately, many of the control settings are implemented within the X and Y deflection amplifiers, so there are no single-ended, ground-referenced tapping points available that can capture all the required info. The most straightforward access to all the original info is to take the deflection amplifier outputs, and convert them from differential to single-ended, and eliminate the common-mode signal originally set up for the CRT deflection plates. This is all easy to do, considering the low bandwidth requirement, and that the signals are quite strong to begin with. I didn't look at the Z-axis yet, but presume it's even easier to pick off. Synchronization and setting signals for digitizing, like from line and the step generator would likely be required, and should be readily accessible. I can elaborate on all this, if anyone is interested.

BTW my main 576's display recently crapped out. I haven't looked into it much yet, but it appears to be a HV failure, even though it is of the later type with the "good" transformer. Hopefully, it will be something minor.

Ed

Join TekScopes@groups.io to automatically receive all group messages.