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Thread: Frustrating Problem

  1. #51
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    Quote Originally Posted by Hugo Holden View Post
    One interesting thing, about the TI sockets, that grip IC pins from side to side, is that the plastic body of the socket can be lifted off the socket pin/claws, to leave them exposed with easy access on the pcb. So the damaged ones can either be repaired, or if they are beyond that, replaced with a pin/claw from a donor TI socket.
    That's only true, AFAIK, for the solder-tail TI units. I think that I remember that the wire-wrap ones are different--I'd have to dig in my stash to make sure, however.

  2. #52

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    Quote Originally Posted by glitch View Post
    I respect the dedication required to actually fix up old TI low-profile sockets! I remove them and replace with high quality machine pin sockets, though.
    Yes, I replace the sockets also if they are too damaged, but, the machine pin ones don't often match the others on the board, so it makes it obvious the board is not original and has been repaired. For that reason I replace with a similar looking dual wipe type. But I still try to avoid changing a whole socket as it is still a thermal stressor on the pcb pads & tracks. Though that can be kept to a minimum with good technique and a good sucker and a temp controlled iron. Most of the issues I have seen is when somebody else has done a bad job replacing the sockets and damaged tracks & pads, for this I use miniature brass eyelets to help with the repairs.

    When I replace DIP switches I replace these with a machine pin IC socket and fit low profile high reliability OMRON switches, that have the same form factor as an IC, this way if the switches fail in the future a new one can just be plugged in.

  3. #53

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    Quote Originally Posted by Chuck(G) View Post
    I used pins from TI gold-plated wirewrap sockets as prototyping board terminals. Just solder them in after clipping off the grabber ends. Honestly, TI sockets were some of the worst ever produced.
    There is a particularly good product sold at Jaycar, a gold plated 0.9mm dia pcb pin and a socket for a flying wire. If the socket is covered in heatshrink and lubricated before use it, you can plug and unplug them many (hundreds) times as they have a very springy phosphor bronze under the gold plating. They are really a help when you need a few connectors here and there on a pcb and I use these in most of my prototype equipment. They are rated at 1 amp, but I would seldom use them for that current.

    https://www.jaycar.com.au/search?tex...d-1df91c6ac355

  4. #54
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    It's simply easier for me to dig into my pile (thousands) of WW socket pins and use those. I'll never last long enough to use all of them. When I do a semi-permanent WW design, I take a hunk of single-sided FR4 PCB stock and drill holes for the pins with a number 48 drill. I seat the pins with an automatic center punch. The copper on the foil side is relieved slightly using a 3/16" drill to cut a slight relief. If the pin is to be grounded, I don't bother with the relief. Produces a very nice and very stable result. For props, you can tin- or silver-plate the copper.

    The benefit is a great ground plane.

  5. #55
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    Well.... the intermittent cloud that has been circling Wisconsin is still in place. I got my Televideo monitor to work. And I wrote a program to continuously test the 8259 PIC in my machine. It ran for a few hours with no errors. So I can discount that as part of the problem. In between this I have checked a few more IC/socket connections and found what I see maybe as a general problem. I found on one of the wire wraps some fuzz. Could not see it bare eyed, but under magnification, it was clear. I replaced the wire and can see the fuzz on the inside wraps. I wonder if there is more of this on other connections? I have tried Hugo's pin test and found at least one socket that I thought should be replaced. Some of this has led to CP/M loading, but it never lasts for more than a few minutes. Then disk errors show up again. I have made some progress. I had some random interrupts which I could not explain, but one of the replacements seem to have solved this. Now I can see that the FDC is issuing DRQ's, the DMA Ctrl is responding with DACK's, I get 128 or these and then get a Terminal Count from the 8237 to the 8272, followed by an interrupt. This is the cycle for reading one sector. And I'm getting the correct floppy sector data in the proper memory addresses. The problem now seems to be, the machine is only reading a few sectors and then quitting. Occasionally only one sector is read most times it is about 15, once in a while it will move to the next track and read a few sectors, but almost never read all the CP/M sectors on track 0 and 1. So while some progress has been made, I'm thinking that I should replace all the sockets on my FDC board, in fact I have ordered a bunch of the new machined ones. Who knows when they will come with all the Christmas mail these days. I did some investigation of the 8272 drive polling and found that the DS0, DS1 and READY lines seem to be working fine. I looked at the WRITE CLOCK waveform and it looks good. The INDEX pulse is OK and so is the TRACK0. I also tried a couple of different 8272 chip. I found one that is definitely bad, but two others will work as above. I want to look at the read data and clock pulse coming from the drives. Maybe there is something there. But why the FDC just stops reading sectors and not the same number of them is still a mystery. Getting closer, Merry Christmas Mike

  6. #56
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    "fuzz"?

    What are you using for wire wrap wire? It should be silver-plated Kynar-insulated solid wire.

  7. #57

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    Any chance the "fuzz" is tin or silver "metal whiskers" which can grow with age?

  8. #58
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    I've used a lot of this wire and have never had any problems like this. It is Belden A.W.M style 1061, 30 AWG solid tinned 0.009" PVC insulation, 9978. The fuzz is very short, I tried to get a picture, but can't focus down that far. It scraps off. I also checked some of the other wires that I replaced and there are no signs of it. Maybe this spool has a length of wire that is missing the tin plating? Mike

  9. #59
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    PVC, tinned? Not for good gas-tight connections.

    You want something like this

    Kynar, silver-plated. I don't even know if you can form a gas-tight connection with tin-plated wire.

    Yes, it's expensive, but you get what you pay for. I buy mine in 1000' foot rolls. You can also get the stuff pre-cut and stripped to lengths--very handy.

  10. #60
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    Well.... that's interesting. I've used this Belden wire for years and have many projects that work just fine for a long time in the power plant. Coal burning produces a lot of corrosive gases. But since I want this card to work consistently and since I have new sockets for it, I may as well use 'good quality' wire. I'm sure there is at least one more gremlin larking on my board. I really would like to know exactly what the problem is, rather than just give up on it, but how much time can I put into it? Sure have gotten to know the PIC DMA and the FDC Intel chips a lot better. Let you know how this works, thanks Mike

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