TDS754d not booting anymore.

[wn1fju]

@poot36:  Thanks, I've seen that web page already, along with dozens of other ones relating to the Tek TDS series.  This current eevBlog thread, however,
is the only one I've seen discussing where the scope seems to completely lock up with an .8 on the diagnostic LED.  Unfortunately, the original author of
this thread didn't submit a solution (if he/she ever found one).

Anyway, there are a few more things I want to check out around the reset circuitry.  What must be a big clue in my particular case was the fact that the
scope seemed to hang earlier and earlier as I kept troubleshooting it throughout the day.  So whatever broke did so somewhat gradually and gracefully. 
Not sure whether that points to an analog failure, such as a capacitor, or a digital failure.  Power supplies all look good.

[wn1fju]

Yay - some progress!

When I got the TDS520 a couple of weeks ago (and it worked fine), I first opened it up and examined all the electrolytic capacitors.  These are known failure
points and the forums are full of warnings to quickly replace them on the 1) processor, 2) acquisition and 3) front panel boards.  My unit had a repair sticker
inside dated 1999 (6 years after it was built) and it was clear that the acquisition board had been re-capped (a lot of them were cockeyed and there were
scratch marks nearby).  I assumed the other two boards were re-capped also.  The front panel board clearly was not since I found puddles of wet electrolyte,
so I re-capped that one.  That left the processor board which was absolutely clean and bone dry with hardly any corrosion on the solder pads - I left that board alone.

So for my present problem with the frozen boot, I did three things:  1) re-capped the processor board and scrubbed it with Simple Green and alcohol several
times (there were no puddles of electrolyte, but there sure was that telltale smell when I desoldered the pads); 2) replaced the 74HCT273 latch that was
driving my diagnostic LED that had gone dim, then completely dark and 3) threw in a new MC68020 uP since it was cheap enough to buy on eBay.

Well, wouldn't you know - the TDS520 now works flawlessly.  Shame on me for not doing the three "fixes" incrementally so I could figure out which one
actually cured it.  As one of my earlier posts said, I already ordered a replacement boot ROM which hasn't arrived yet, but obviously that was a waste of
money.

We will see how long all this lasts.....  Hopefully at least until tomorrow!

[poot36]

Good job of finding the issues.  Sorry I lead you down the rabbit hole with the firmware replacement.  Could you at least dump it so that if someone needs it they have it?

[james_s]

I would not be the least bit surprised if the entire problem was caused by the capacitors. Puddles of electrolyte on the front panel could have been jamming up the bus and getting it into who knows what state.

[wn1fju]

@james_s:  If it was a cap failure, it was definitely on the processor board.  I had already re-capped the front panel board and it was working for a few
days after that.  I'm wondering, however, if some of the caps on the processor board ultimately lost their capacitance.  Almost all of them are on power
rails, but I see one that sets the timing for the TL7705 chip that controls the 68020's reset circuitry.  That might upset things.

@poot36:  I do have the boot ROM file for TDS520 version 1.5, Tek part number 160-8505-00.  I'll see if I can post it here tomorrow- I have to transfer
it over from a different computer first.

[picburner]

If in the future someone needed it you can find many Tek eprom images here: http://w140.com/tekwiki/wiki/ROM_images including the one for this scope.

[wn1fju]

@picburner:  Many thanks for the link to the ROM images.  Would have saved me $25 had I known about this!  I swear I did a google search for the ROM
images a couple of weeks ago.  I don't know what I was thinking then, because when I now google "Tektronix TDS520 ROM Image," there it is in plain view.

Oh well, no need to post my image.  And I did verify that my image equals the link's image (as expected since my scope is working).  So that also confirms
that the diagnostic flow chart in the service manual that lists the first four bytes of the ROM has a misprint.  Fourth byte = FE, not FF.

[analogRF]

can anybody show/tell me where the serial console on TDS784D is located?
the tek forum link that was posted earlier in this thread is dead now

thanks

[madao]

Here-   (TDS540A, but console port is same at position, near  LTP/RS232 Interface )


@wn1fju  I have uploaded   TDS520 Firmware to KO4BB Site (of coruse,12x file for EPROM )  But,  "readme.txt" tells , it is for TDS524A, it is my fault 
It is newste  Firmware for TDS520 (Version 2.16e)