Topics

7D20 with unknown options or mods


Richard Steedman
 

I have a 7D20 with a couple of modifications or options added. Can anyone provide some information about these?

The first is a board sitting on top of board A11 above the vacant IC sockets U1230, U1330 and U1430. It has a connector P200, connected to J100 on the CCD board A5. It has three ICs - a dual 4-input NOR gate, a quad analog switch/mux and a dual op-amp. One of the 7D20 photos on Barry Johnson's website looks like it has the same mod (http://www.barrytech.com/tektronix/tek7000/tek7d20top.jpg).

The second is a small board sitting behind the front panel in-between boards A6 and A7. It's connector has flying leads soldered directly to pins of the CCD chips on the underside of board A5.

I have posted photos here.

The 7D20 has a serial number in the B085000's and is running firmware F1.03. Any insights gratefully appreciated!


Chuck Harris
 

As I recall, there was a variation of the 7D20 that was called
the 7D20T, that fit in its own chassis, and was used in conjunction
with computers to gather data.

A picture is shown on page 338 of the 1984 TEK Products catalog.

-Chuck Harris



Richard Steedman wrote:

I have a 7D20 with a couple of modifications or options added. Can anyone provide some information about these?

The first is a board sitting on top of board A11 above the vacant IC sockets U1230, U1330 and U1430. It has a connector P200, connected to J100 on the CCD board A5. It has three ICs - a dual 4-input NOR gate, a quad analog switch/mux and a dual op-amp. One of the 7D20 photos on Barry Johnson's website looks like it has the same mod [(http://www.barrytech.com/tektronix/tek7000/tek7d20top.jpg)](http://www.barrytech.com/tektronix/tek7000/tek7d20top.jpg).

The second is a small board sitting behind the front panel in-between boards A6 and A7. It's connector has flying leads soldered directly to pins of the CCD chips on the underside of board A5.

I have posted photos [here](https://groups.io/g/TekScopes/album?id=253175).

The 7D20 has a serial number in the B085000's and is running firmware F1.03. Any insights gratefully appreciated!




Clark Foley
 

Chuck,

The 7D20T did not require anything extra from the 7D20. Any production 7D20 will function in the T package without modification. You could add the rear access cable for the GPIB that had a companion mod for the R7603. The mainframe for the 7D20T has the necessary 7k interface, rear GPIB wiring and power in a TM5003 skin (the notorious modular package system (MPS)).

Regards,
Clark Foley


Chuck Harris
 

Ok,

But there was an option on the 7D20 that made it work with
the 7854 digital storage scope. Perhaps that is the option
you seek?

-Chuck Harris

Clark Foley wrote:

Chuck,

The 7D20T did not require anything extra from the 7D20. Any production 7D20 will function in the T package without modification. You could add the rear access cable for the GPIB that had a companion mod for the R7603. The mainframe for the 7D20T has the necessary 7k interface, rear GPIB wiring and power in a TM5003 skin (the notorious modular package system (MPS)).

Regards,
Clark Foley




Clark Foley
 

Richard,

I can consult my micro fiche file for factory modifications. It's a bit tedious and slow to paw through the film, but I'll have a look.

Clark


Clark Foley
 

Richard,

I found some clues about the little board on the Timebase board. It is named "ERD Shift Adjust." ERD is a digitizing mode called "extended real-time digitizing." The little board allows for additional vertical offset correction to the CCD output depending upon the time/div. Without it, you will see a small but irritatingly noticeable vertical shift to the waveform as the time/div is changed in the ERD range. Apparently the original adjustments were not quite enough to cover the entire ERD range. I recall, from long ago, that some of the CCDs produced more voltage offset than others depending upon the clocking frequency; something to do with variations in transfer efficiency. Usually CCDs were clocked at a fixed rate and the offset is adjusted or cancelled by some external circuitry. ERD mode will operate the CCD at a rate unique determined by each time/div setting; hence, the extra offset adjustment. Anyway, that board is standard equipment on later units and not a custom trick for a special customer.

I don't know what the other mod is that has four wires soldered to the CCD. If you are able to tell me which CCD pins, I might be able to find a clue.

Clark


Richard Steedman
 

Thanks Clark, Chuck. Very interesting. The leads to the CCDs don't appear to be connected to any of its DIL pins. They look like they are soldered directly on to the substrate. The SL92104 looks a quite complicated MCM affair. I'm not sure I want to go poking around there! I haven't been able to find a datasheet for the SL92104 chip. Any idea whether such a document exists?


Clark Foley
 

Richard,

I found what I believe to be the same part. The pins and functions are the same, but under a different part number. I don't remember if Tek had them screened or selected for critical specification. The commercial Fairchild part number is CCD321A Analog Video Delay Line. I have posted the Fairchild data sheet to this site as a File (Fairchild_CCD_VideoDelayLine_PossilbleSL92104.pdf). The file is 5Mbytes.

It is possible that the four wires might be supplying power to a pair of thermo-electric coolers (a.k.a. Peltier coolers or reverse Seebeck). This is my guess without seeing what is actually attached to the ICs. I would have to pester one of the designers to confirm.

Clark


 

On Thu, Sep 10, 2020 at 09:52 PM, Clark Foley wrote:


I have posted the Fairchild data sheet to this site as a File
(Fairchild_CCD_VideoDelayLine_PossilbleSL92104.pdf).
https://groups.io/g/TekScopes/files/Fairchild_CCD_VideoDelayLine_PossilbleSL92104.pdf

Raymond


Richard Steedman
 

The cooler theory seems plausible. Assuming that the SL92104 and CCD321A are basically the same device, then whatever the leads are connected to is not part of the chip.