B&F Enterprises "Digital Clock" flakes out

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7 years 6 months ago - 7 years 6 months ago #4868 by Ty_Eeberfest
Oh, it's repairable. Just depends how much time and effort you can put into it ;)

Let us know when you've gone over the solder joints, etc. Speculating on components is IMHO pointless until that's done. And yeah, real flux remover and an old toothbrush rocks, 91% isopropyl is more like a second rate emergency substitute. If you can get real 1,1,1-Trichloroethane, use it. The MG Chemicals heavy duty stuff in sprat can ain't bad either.

Regarding the resets, the 7490s have 4 (!) resets per chip and the 7492s have 2. Here's your data sheet...

EDIT: Doing it as an attachment is failing for some reason. Here's the link to where I got it.

www.ti.com/lit/ds/symlink/sn74ls90.pdf

Look into it later when the dust is clearing off the crater.
Last edit: 7 years 6 months ago by Ty_Eeberfest. Reason: PDF Attachments Failed

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7 years 6 months ago #4869 by Dr. Optigan
Well, I opened the clock, and did another tap test around the ICs. Got flickers from other tubes then, once I tapped underneath one of the 7490s (the lone '72 original), it started counting again. I know I'm not out of the woods yet, but at least it's not still stuck. :) Gonna examine all the solder joints in the area once I can get a good magnifier, and might reflow all of the suspect IC's joints with the soldering iron just to be sure.
-Adam

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7 years 6 months ago - 7 years 6 months ago #4870 by DekatronNixie
Replied by DekatronNixie on topic Re: B&F Enterprises "Digital Clock" flakes out
Hi,

Having looked at your photo with the components I suggest that you check pin number 4 and 12 of the 7490 (stamped with date code 7227) as the strip sockets used there seems to be "open" more than the other pins. You can lift the ic's out of their sockets and very gently push these sockets closed again, but don't press to hard as it will be problematic to put the ic's back again.

While you are at it you should check each and every ic socket and in your case it might help to just remove the ic's and put them back, the corossion that can build up over the years in these sockets can be part of the problem.

I would also replace the red drop formed tantalum capacitor as those are known to short and burn when they get old. I have replaced hundreds of those, most before they have exploded but a lot after they have exploded and then I had to replace components close to them and clean the PCB's. It looks like it says "10" and "25V" on yours, then it is 10uF/25V.

/Martin
Last edit: 7 years 6 months ago by DekatronNixie. Reason: corrected spelling

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7 years 6 months ago #4871 by Dr. Optigan

DekatronNixie wrote: Hi,

Having looked at your photo with the components I suggest that you check pin number 4 and 12 of the 7490 (stamped with date code 7227) as the strip sockets used there seems to be "open" more than the other pins. You can lift the ic's out of their sockets and very gently push these sockets closed again, but don't press to hard as it will be problematic to put the ic's back again.

While you are at it you should check each and every ic socket and in your case it might help to just remove the ic's and put them back, the corossion that can build up over the years in these sockets can be part of the problem.

I would also replace the red drop formed tantalum capacitor as those are known to short and burn when they get old. I have replaced hundreds of those, most before they have exploded but a lot after they have exploded and then I had to replace components close to them and clean the PCB's. It looks like it says "10" and "25V" on yours, then it is 10uF/25V.

/Martin


Thanks for the suggestions! I indeed suspected that 7490, though it's not the only issue. I tried re-tensioning those pins as best I could, and cleaned each pin socket with DeOxit, but it didn't have too much of an effect. I then ended up using needlenose pliers to squeeze the pin sockets on opposite sides of each of the counter ICs closer together, and so far that has held. I'm definitely not ready to call it cured, but it's held up for over 15 hours thus far.

I can see why they stopped using these 'strip sockets', and switched to more-conventional plastic sockets. I'm not entirely sure why the builder ended up using these things in the first place, as they don't seem to hold the pins very securely. Guessing it seemed like a good idea at the time... :pinch:

Yeah, I'm planning to replace that tantalum cap in the near future. Would it be OK to use a conventional electrolytic capacitor in its place? I'm guessing the tantalum cap was used for its reduced size characteristics, and not the other advantages they're said to have over conventional electrolytic caps.
-Adam

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7 years 6 months ago #4872 by DekatronNixie
Replied by DekatronNixie on topic Re: B&F Enterprises "Digital Clock" flakes out
You can use any ordinary electrolytic capacitor instead of a tantalum. Tantalum capacitors were often used for their reduced size and also because they were "popular" but some break down with a large bang and burn and semll awful so I usually replace old ones on sight.

Yes, those strip sockets were a lot cheaper when they came and you could easily do whatever size of socket that you wanted, you just had to cut off any number of pins from the role. You did not have to have drawers full of different size sockets.

New sockets should not set you back much with todays low prices.

/Martin

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3 years 11 months ago - 3 years 11 months ago #7183 by Dr. Optigan
Hello again, everyone! Figured I'd give a long-overdue update about this clock. Some friends of mine worked on it a few years ago, and it's been working mostly glitch-free ever since. It's had the filter capacitances increased, the internal wiring has been replaced, and those cursed strip sockets are long-gone! :woohoo:

Anyway, a remarkable thing happened recently: I heard from someone who built one of these B&F Enterprises clocks back in the early 1970s! He's been having issues with it (I'm not surprised), but managed to save the paperwork which originally went with it, which he was kind enough to send me a scan of! It's not in the best shape, but he cleaned it up, and it's decently readable. Below is an image of the long-awaited schematic:



I have also created PDF files of the instructions , and the associated diagrams (which includes the schematic). Enjoy!
-Adam
Last edit: 3 years 11 months ago by Dr. Optigan.

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