TDS784D: Recovery from Bricked state

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kc7gr.roadie
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TDS784D: Recovery from Bricked state

Post by kc7gr.roadie » October 12th, 2017, 9:16 am

I've decided to start a new thread as a spinoff from the previous: viewtopic.php?f=568&t=139999

The short version: I have a TDS784D which, through some mistakes on my part, has become 'bricked' (as in won't boot, just sits there with a blank screen). The original CPU board was part #679-4172-00 which, as I understand it, can only accept firmware up to 6.6e (the last load, the one which was working and which I've been unable to restore a backup of, is 6.5e).

Last night, I tried installing an updated CPU board, part 679-4349-00, taken from a known-working TDS724D and bearing firmware version 7.4e. The results were both interesting and frustrating: This time, the unit starts its boot process and gets past the 'Digital Phosphor Oscilloscope' splash screen and the initial turn-off of all the front panel LED indicators.

However, at that point, it hangs. Once again, it just sits there with a blank screen and non-responsive front panel buttons.

I've watched the seven-segment LED display on the CPU board during the boot process. After the initial count-up, during the portion of the boot process which displays the splash screen, the top and bottom segments (c and f) flash alternately about twice per second. When the boot process stalls, this alternating flashing stops with the bottom segment (c) steadily lit. I'm guessing the alternate flashing means 'Everything's OK, software running normally.'

First Question: When a replacement CPU board is installed in a scope different from what it was in before, is there some sort of 'initialization' or 'reset' process I need to do before the thing will work? Perhaps there's a 'factory reset' trick by holding in certain buttons during power-up?

Second question: Does the scope put out console status messages to the RS232 port during boot-up? Or do I need to kludge some sort of console monitor for it? I'm thinking if I can see, exactly, where the process is hanging up it'll give me a good clue where to go poking around next.

Some tricks I'm considering: Adjusting the ID jumpers on the acquisition board, temporarily, to make it ID like that of a 724D. I've already tried moving the NVRAM chips around between boards (I converted both the original CPU board and my replacement to sockets for both Dallas chips), and that didn't seem to help.

Thoughts welcome. Thanks much!

strick
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Joined: March 22nd, 2016, 11:23 am
Country: United States

Re: TDS784D: Recovery from Bricked state

Post by strick » October 12th, 2017, 10:45 am

Changing the processor board should not bother the scope with this later series. Older versions like the 544a would complain when you put a 524 processor board in (was looking for 4 channels, only found two). But the scope would boot and you could see what was going on.

I've never had a 744D to swap out, but I've done it many times with other 5/700A/B series... However, I would love to hear some other folks (like Cap) chime in if they have a different opinion.

There is no magic reset unless you consider running the calibration routine as select "cold start". But, look in the TDS-520B component service manual and you can set the dip switches (S1001) on the processor board to skip certain tests (page 1-53). As I recall, placing switches 7 and 8 to the 1 position will skip all bootrom tests and may get you into the scope.

The serial port is just that, a serial port for a printer. There is a way to rig up a "debug" device using the same option 13 board (which has the parallel/serial ports) and connect to the rear (unused) port on the rear of the board. Search for debug and serial port on this board and you should find it.

good luck

kc7gr.roadie
Posts: 14
Joined: October 5th, 2017, 12:14 am
Country: United States

Re: TDS784D: Recovery from Bricked state

Post by kc7gr.roadie » October 12th, 2017, 1:34 pm

I think I just figured out what the problem is.

My original 784D was made prior to serial B04xxxx (as I recall, it's B01xxxsomething). This means it has an early-version acquisition board.

The CPU board I put in came out of a scope with a much later B04xxxx series serial number. In that later series, the acquisition board went through some hardware revisions as well.

My conclusion: The later-model CPU boards will not talk to the early-model acquisition boards. :!:

(sigh) OK -- Well, the good news is I can at least continue my efforts with the original CPU board. In retrospect, I think the reason I've not been able to restore its flash is because I wasn't using an ISA-based GPIB card. That's arriving today, so I get to try again. Even then, I've still got the option of physically pulling the flash devices off the board, reloading them in my Unisite and reattaching them.

I will also be looking out for a late-issue acquisition board. No matter what, I'll post an update with whatever results I come up with.

My deepest thanks to all who commented. I've learned a lot more about the TDS series than I ever dreamed I would! :D

kc7gr.roadie
Posts: 14
Joined: October 5th, 2017, 12:14 am
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Re: TDS784D: Recovery from Bricked state - IT LIVES AGAIN!!!!

Post by kc7gr.roadie » October 14th, 2017, 12:26 am

Strick, you are a certified miracle worker! :D

I'm delighted to report your tektool_0 file (the correct one to use, since my 'scope has the earlier CPU board with 28F016 flash chips), plus setting up an ISA-bus based GPIB card (an AT-GPIB, to be exact, under Windows 98SE), has resulted in my 'scope becoming fully functional once again. I'm bloody glad I saved a backup of the firmware before I ever started experimenting, because I certainly needed it.

Also, please note! There are differences in the version of CPU and Acquisition board used on the TDS7xxD series, and NOT all firmware loads are compatible with them. I would strongly recommend checking both the serial number AND doing an actual visual check of the part number labels on the boards before you even think of messing with firmware updates.

Specifically: Serial numbers LOWER THAN B04xxxx will likely have CPU board part number 679-4172-00. This board is NOT compatible with anything later than firmware version 6.6e, nor is the acquisition board which it pairs with.

Serial numbers of B04xxxx and higher will likely have CPU P/N 679-4349-00. This board, and its matching acquisition board, need firmware version 7.4e to work (other versions in the 7.x series may work as well; That would be a question for Tek support).

For anyone else who's considering working with Tektool: Your GPIB card should be a genuine National Instruments item, either the AT-GPIB or the GPIB-PCII/IIA, and whatever computer you use is going to need at least one ISA slot (8-bit for the original PCII/IIA, 16-bit for the AT-GPIB or the PCII/IIA) to accommodate said card. As for an OS, Windows 98SE, with NI's drivers for the card.

Yes, you'll likely have trouble finding an ISA-capable desktop system these days, even on the used market. One trick which may help you is to look for the industrial-class PC's, with the passive backplane and single-board computer modules. The combo ISA and PCI form factor will do if you can't find an all-ISA, as long as the backplane has ISA slots. I was lucky, as I had an old Dell XPS hanging around (all but one of its expansion slots are PCI, and that one exception is 16-bit ISA).

Now, if you'll excuse me, I just have to put the outer case back on and stick the thing back on my bench.

THANK YOU!!!

strick
Posts: 36
Joined: March 22nd, 2016, 11:23 am
Country: United States

Re: TDS784D: Recovery from Bricked state

Post by strick » October 15th, 2017, 5:55 pm

Excellent! Glad to help and thanks for the detailed FW dump. On the earlier 500/700A-C scopes that I've dealt with didn't seem to be quite as particular with the version of FW. I've often swapped an older FW board onto an acq board and they did fine.

Strick

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