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Electronics => Repair => Topic started by: Johnny10 on January 11, 2018, 06:22:52 pm

Title: Tektronix TDS784D Mixed Acquisition and CPU Boards
Post by: Johnny10 on January 11, 2018, 06:22:52 pm
I recently picked up a TDS784D parts unit which may actually be a "parts unit".

Upon opening I found loose boards nothing connected.
And mixed Acquisition and CPU boards.

The serial  number is B0409xx
Acquisition Board 671-4164-02
CPU/Dram Board 679-4349-00

I can only get to the Tektronix Screen on start-up.
Wondering if this has to do with mismatched boards.
Title: Re: Tektronix TDS784D Mixed Acquisition and CPU Boards
Post by: ArcticGeek on January 11, 2018, 08:04:23 pm
Your hunch is correct.   

According to the TDS784D Service Manual, the part number for the acquisition board is correct for a TDS784D.  However, the CPU board that you have does not match what the manual states.  According to the manual, the part number for the processor board is 671-4172-00.  I suppose it's possible that Tek produced a newer revision board and didn't update the manual, but I doubt it.
Title: Re: Tektronix TDS784D Mixed Acquisition and CPU Boards
Post by: Jwalling on January 12, 2018, 10:56:19 am
Serial prefix B040XXX should have burst / synchronous memory. Yours has SRAM, which leads me to believe that the ACQ board is incorrect for your unit.
If you do a Google search on 679-4349-00 you'll get a number of hits for TDS784D and TDS754D, so the CPU board could be correct for B040XXX - it's hard to say...

For now, make sure switch #3 is in the off position on the CPU board when you power it up and see if it POSTs OK. This will make the scope skip most of the self tests.
Title: Re: Tektronix TDS784D Mixed Acquisition and CPU Boards
Post by: Johnny10 on January 12, 2018, 06:35:17 pm
More research in the board descriptions from the Service Manual shows that 671-4164-02 was used in Serial numbers up to B039999.
Then Acquisition Board 671-4770-01 After Serial # B040100.

Another site Keithley/Tektronix forum had a member that had CPU/Dram Board 679-4349-00 in a later series unit same as mine.

Going to be reading up on his attempts which match mine. Locked at Tektronix Splash screen.

Thanks for the ongoing suggestions. I tried changing Pin 3 but to no avail.

Title: Re: Tektronix TDS784D Mixed Acquisition and CPU Boards
Post by: Jwalling on January 13, 2018, 11:22:48 am
I think you'll have to score a new CPU board from an older scope to fix this, assuming that the CPU in your scope is for B040XXX. Serial prefix B040XX acquisition boards underwent a major re-design. Besides what I mentioned above, they combined the 4 A/D converters and MUX into one single chip, and the chips between the ACQ memory and A/D converters went from a 308 pin quad flatpack to BGA.
Title: Re: Tektronix TDS784D Mixed Acquisition and CPU Boards
Post by: andy2000 on January 13, 2018, 04:48:34 pm
You could try downgrading the firmware on your CPU board.  This would work if the CPU board doesn't have any significant hardware changes. 
Title: Re: Tektronix TDS784D Mixed Acquisition and CPU Boards
Post by: charlyd on January 13, 2018, 06:12:25 pm
for sure Jay  is right you need a  ACQ board: http://s32.postimg.org/t29kr56it/IMG_20160520_095728.jpg (http://s32.postimg.org/t29kr56it/IMG_20160520_095728.jpg)
Title: Re: Tektronix TDS784D Mixed Acquisition and CPU Boards
Post by: Johnny10 on January 13, 2018, 07:30:15 pm
Yes, I see that after more research into this issue.
Looks like I need a different acquisition board to match CPU board.
Acquisition Board 671-4770-01

I started looking today, made an offer on one we will see.

Not sure when they stopped making these units my 671-4164-02 acquisition board has a job sticker from 2004?

I know this unit was in for repair and left for parts.
Title: Re: Tektronix TDS784D Mixed Acquisition and CPU Boards
Post by: Jwalling on January 13, 2018, 08:28:22 pm
Yes, I see that after more research into this issue.
Looks like I need a different acquisition board to match CPU board.

Or an older CPU board, which is likely to cost less anyway.
Title: Re: Tektronix TDS784D Mixed Acquisition and CPU Boards
Post by: and.pas on June 19, 2019, 05:57:20 am
Hello Johnny,
I wonder if you eventually fixed your scope somehow...
I have a working TDS754D serial B01xx, which could be compatible with your ACQ board.
In case you are not employing it in your final setup, are you in willing to sell it?

Thanks
Andrea

Title: Re: Tektronix TDS784D Mixed Acquisition and CPU Boards
Post by: Johnny10 on June 19, 2019, 09:27:57 am
Yes, I did fix this unit and sold it.
Took about 4 months to find another broken unit.

Wish I would have kept it... it had fast boot up and was smaller than my new bench scope which is TDS7104.

I would have to look through my parts inventory.
What do you need exactly?

Title: Re: Tektronix TDS784D Mixed Acquisition and CPU Boards
Post by: charlyd on June 19, 2019, 05:30:11 pm
Jay is right, the board should be the newer version 679-4349-00 but you should get your scope wake up with an older board if it is ok. i repaired many of these.. and the best to do is try to get the console port connected.  after powering on...
Here how to build it,  i created a topic on it on the tek forum long time ago,
console port for dummies the topic is called:

http://i65.tinypic.com/f5acye.jpg (http://i65.tinypic.com/f5acye.jpg)