[Success] Conversion Tektronix TDS620B to TDS680B to TDS644B/TDS684B

[Nx-1997]

Hi, so I finally decided to open my 620B and see if I can somehow convert it to a higher model. I had to remove the acquisition board and flip it, this allowed me to locate the four ID resistors near the two eeproms that store calibration data. What interesting about this resistor config is that two of the pads are populated with 1M ohm resistors.
 
I decided to invert the resistor config and that seemed to have converted the scope to 680B. I tested the scope and found that although the 5GS/s sampling worked I was not able to get 1GHz bandwidth.

But I don’t really care about that. What I want is to convert it to 644B/684B so that I can have all four channels on screen at the same time. So, I desoldered all the resistors and attached some wires in their place. I started going through all the possible combinations, but I couldn’t really get the 644B or 684B model on the screen. All I get is 620B or 680B on the screen. I am positive that the 600B series all have the same acquisition boards.

I need pictures of 644B/684B/684C of the acquisition board and the digital board. I think the scope is using the Acq board ID resistors and the ID resistors on the digital board to identify if its a 680B (Mono) or 684B (Color).

Any help would be grateful.

[Nx-1997]

Ok, so I removed the R12 resistor on the Digital board and that seems to have worked. I have converted my 620B to 680B to 684B. All channels can now be on the screen and they all work perfectly. I have not tested the 1GHz bandwidth, but the 5GS/s sampling is now present for all channels and it works.

Now, only one issue remains, the CRT has a white overlay and I can’t really get rid of it and it is also present on the VGA output but only in the waveform display area. I think this has something to do with the fact that the digital board is missing some chips which are obviously present on the 684B scopes. what the VGA output looks like: https://streamable.com/lo9jyy

I am still looking for 644B/684B pics of digital and acquisition boards.
Any help would be appreciated on this matter.

[Jay_Diddy_B]

Hi

Read this thread:

https://www.eevblog.com/forum/testgear/conversion-of-500mhz-tds744a-to-1ghz-tds784a/msg568463/#msg568463

I solved the bandwidth problem by studying high resolution photographs of spare parts on eBay.

There are probably some capacitor to remove that are limiting the bandwidth.

You may find out if the 684B boards are fully stuffed.

Regards,
Jay_Diddy_B

[Nx-1997]

Yes I have seen your work. Thanks to you I was able to upgrade my 754D to 784D, but the 600B series has a different architecture. I don't see any difference between the 600B Acc boards. Currently, I am only looking to solve my VGA output problem. I think I might have to order the Video RAM chips according to this link: https://www.eevblog.com/forum/repair/conversion-tektronix-tds500-to-tds700-color-oscilloscope/

Sincerely,
Nx1997

[Jwalling]

If the board is like the TDS654C, then the four caps to be removed are located under those 4 NS flat packs on the solder side.

[Nx-1997]

Well, I finished converting my TDS620B to TDS684B. From 2 channel on-screen to all 4 channels. Bandwidth increased from 500MHz to 1GHz, sample rate from 2.5GS/s to 5GS/s. I tested the 1GHz bandwidth, its OK, 1V rms at 100MHz, 0.717mV rms at 1GHz. I removed the 4 resistors and 4 capacitors on the acquisition board. Removed resistors R151, R152, R153, R12 on the digital board. And populated the video ram(TC528257J-70) using sockets soldered to the board. I also replaced the CRT to 8 inch 4:3 anti-glare matte LCD, I had to cut through the front panel plastic as the LCD was too big.

[shakalnokturn]

Good hack! Thanks for documenting.
A pity for the LCD...

[madao]

Great !


You have convert from TDS620B to TDS680/684B with same acquisition board, correct?
It is really funny,   Tek  build  full 4 channel and limited him to 2 ch.

It means: You can buy  TDS620B/624B and convert him with change of resistor-ID to 4ch models for zero cost. 

This way is not possible on  TDS500/700, because  half of IC is missed.


TFT-replacement look a bit wreid, but,  bigger TFT is good for old men   
I have here  four  6.5" TFT Panel with VGA-Input board for  1:1  replacement of CRT in TDS500/600/700 family.

greetings
matt

[Rollin Hand]

what tft board did you use? and what vga driver did you use?
clean mod ,tanks for posting.

[Nx-1997]

Yes. All TDS620B, TDS680B and TDS644B can be upgraded to TDS684B without replacing any digital or acquisition boards. Similar hack are also possible for the TDS600C series and possibly for TDS600A series. Soldering the sockets for the VRAM is time consuming and required a microscope.

[Nx-1997]

The LCD used in this mod is the HJ080IA-01E, costs around $30 USD on aliexpress, it comes with the driver board.

[holgerinput]

How do the menu buttons line up to the menu entries now?

[coromonadalix]

take a marker   and do some lines on the front panel case, sure its not elegant, but better than nothing ?

[Nx-1997]

The buttons don't match the menu entries, it not a big deal for me. You get use to it. Obviously, you can get a smaller 4:3 LCD but they cost $100+ and this was the one cheap one I could find. I did a similar LCD mod (got the reflective screen instead of matte ) to my tds784d (upgraded from 754d). The picture looks washed out but in real life the LCD is really good.

[Shonky]

Bit of a thread dig, but seems appropriate as this seems the best source of info on upgrading these.

I have a TDS644B so already have the colour screen, 4 channels and looks like most/all of the major missing components are factory fitted.

The digital board is already missing the R12 and the other resistors nearby are the same config as pictured (from the factory so standard spec).

It has R151-R153 missing as it's colour already.

Do the R106x resistors contribute to how it identifies itself? I haven't found them yet. Are they on the inside side of the Acquisition PCB?

[TERRA Operative]

Do the R106x resistors contribute to how it identifies itself? I haven't found them yet. Are they on the inside side of the Acquisition PCB?

They can be n the front or the bck of the acquisition board, depending on board revision. Usually somewhere around where the 4 blue coax cables connect.