Man that's a really nice outcome! I'm not familiar with that "dreaded" issue, what is it that fails - only the board? Why does it fail?
I have a lot of test equipment but just recently started the Tek TM500 series journey myself. I actually used that stuff in industry in my career, so I wanted to get some of the same items that I used on a daily basis. I don't have that particular counter but I do have the DC 504. I'll have to keep an eye out for the DC 508.
You can see my collection in the pic, I don't think I've posted a shot of it all yet. Well, one is missing that's on the bench - an FG 502 that's been a little bit of a project to get going but we're nearing the end of the repair.
Look forward to more of your repairs, and remember we love pics!
Ok, the original 3 digit 7 segment display part is the weak link. Eventually, all of them will fail. It is a time thing, I guess. But the board itself is ok. The Tek engineers decided to socket the 4 status LEDs on the board. I guess thinking that they would be the weak links. Funny how the opposite happens sometimes.
Anyway, the DL883A part (I forget the Tek part number) does have a NSN number assigned to it. So you actually CAN get them. I got a quote of ~$600.00 each. So yeah, I still consider that part as made of unobtainium. There are quite a few pieces of TM500 modules that used this part. Your DC504, for example. It has 2 DL882A 2 digit displays paired with 1 DL883A 3 digit displays. A lot of people bought DC504s to repair their DC508s. However, the DL882/3A parts are VERY sensitive to heat and I lot of them were destroyed in the removal/replacement process.
Not to mention it ends the life of the poor DC504. In my DC508's case, there was a dead segment in each of the 3 display parts. So I would have to find 3 DC504s with good DL883As in them and pray to the gods of 7 segment displays that I didn't tear them up in the scavenging process.
The later DC504As don't have these displays and use something more like a modern display. However, I don't know if there are any drop in replacements for these at all, as the pin outs / footprints may be strange by today's standards.
So, if you are looking on auction sights, beware of sellers offering a DC508(A) if they don't show them powered up. Pressing the reset button doubles as a display test function where it lights up every segment on the display. I say this even knowing that a lot of guys on this thread might prefer a DOA challenge. But for those that want a functional DC508(A), caveat emptor!
DC508(A)s used to be on eBay all of the time. Now, not so much.
I just tested this DC508 against my Racal Dana 1992's 10MHz standard. Seems to be spot on. It is nice when all of your equipment's time bases seem to agree.
Now I need to take a look at my DC504A and figure out why it is so deaf. It takes max rated input signal strength to get it to work.
Steve