Thoughts on desoldering a component on a 30+ year old retro computer

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Lizard1977

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#288375 24-Jun-2021 14:07

I've been enjoying retro computing the last few months, upgrading my Amiga 500 with new features (RGB2HDMI, a GoEx floppy drive emulator) but the latest project has caused some damage. I was installing a switching socket that would let me switch between the original internal floppy drive and the new GoEx drive (installed as an external floppy drive) for booting, but the 34-pin floppy header on the motherboard got damaged, and one of the critical pins broke off/came out.

As far as I can tell, the only real solution is to desolder the old floppy pin header and solder in a new header. However, this is beyond my usual skill level with a soldering iron. I'm hoping to draw on support from my local makerspace, but I wanted to check with others that may have experience in modding/soldering with older computers. Is there a practical alternative to what I've outlined?

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#2733810 24-Jun-2021 14:15

Photos would be very helpful !

frankv

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#2733842 24-Jun-2021 14:55

Yeah, photos would be good. But I assume it's a 2x17-pin header at the usual 2.54mm spacing. In which case, you might get away with cutting the header between 2 pairs of pins, leaving maybe 15 pairs in place and removing 2 faulty pairs. You could then get a 2x2-pin header (or cut 2 pairs of pins off a larger header) and solder it into the right place. With a bit of care and luck, everything will line up enough for the connector to go over all 34 pins.

But... removing/replacing headers is probably the easiest soldering repair task you'll come across, because there's no particular issues around putting too much heat in. Think of this as a learning opportunity to gain some skills that will likely be useful in the future if you continue to dabble with older computers.

Worst case, a connector is just a connector. It doesn't have to be all in one piece. You could solder on a couple of jumper wires to another (say) 2-pin connector, add the opposite on your floppy drive(s), and you'll be good to go. A bit of a bodge job that you wouldn't want anyone else to see, but probably serviceable enough.

JaseNZ

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#2733844 24-Jun-2021 15:00

I do a fair bit of soldering on old gear, I always combine a low melt solder onto the component first just makes it so much easier for removing things. Just my 2c

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elpenguino

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#2733869 24-Jun-2021 15:58

Lizard1977:

As far as I can tell, the only real solution is to desolder the old floppy pin header and solder in a new header.

It's not the only solution but it would lead to your retro device looking less bodged than otherwise.

Replacing through hole components like that is relatively easy. I speculate you could rob a replacement socket from anything else that had a floppy device such as an old PC motherboard etc.

I'd be happy to help if you're in Wellington.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

MadEngineer

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#2733972 24-Jun-2021 18:33

Ditto if Manawatu

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Lizard1977

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#2733989 24-Jun-2021 19:37

Here's what the missing pin looks like.

Here's the reverse side of the board. The double row of pins just above centre are the header pins. I can't see a lot around the area which looks especially delicate.

I got in touch with the local Makerspace in Palmerston North here and they are going to help with the desoldering. I had a look at Jaycar and found this 40 pin dual in line component which I think should be fine - just snap away what I don't need, and solder it in place. Thanks @frankv for the suggestion of just cutting away the missing part and soldering in a 2x2 replacement section. I'll keep that in mind - if desoldering proves problematic that might be a simpler solution. But it might pay to replace the whole component, especially if there's a chance that other pins might fall out.

gbwelly

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#2734005 24-Jun-2021 20:41

Did you flip it left to right between pictures or top to bottom?

Did it actually go anywhere on the back of the board? If it wasn't soldered in, perhaps that is why it dropped out. Maybe you don't need to do anything.

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frankv

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#2734017 24-Jun-2021 21:10

I'd be inclined to just try putting the missing pin back in. (If you've lost , extract one from a header). Hold the pin with long nose pliers, and heat it if necessary to go through the hole in the plastic header. Maybe desolder the hole from the back of the board, and the pin will go into place. Otherwise heat the pad on the back of the board while keeping pressure on the pin from the front. With a bit of luck it'll go into the hole.

If the pin is a bit crooked, heat the pad again while you straighten it.

neb

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#2734037 24-Jun-2021 22:47

Lizard1977:
Here's what the missing pin looks like.

If it's just a single pin missing, could you use a dremel to drill out the hole and then solder in some appropriate piece of conductor to replace it?

Lizard1977

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#2734069 25-Jun-2021 08:17

Thanks guys,

I did wonder about replacing just the pin that's missing. It might be worth trying in the first instance and if that doesn't work then replacing the strip.

elpenguino

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#2734096 25-Jun-2021 09:31

Lizard1977:

Thanks guys,

I did wonder about replacing just the pin that's missing. It might be worth trying in the first instance and if that doesn't work then replacing the strip.

Yep, that can be done and it wouldn't look too bad - see the other comment about straightening it.

Once the donor pin is hot it will just slide out of the plastic housing under plier tension.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

gbwelly

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#2734124 25-Jun-2021 10:16

Have you established if the pin actually does anything before you bother fixing it?

Lizard1977

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#2734147 25-Jun-2021 10:51

gbwelly:
Have you established if the pin actually does anything before you bother fixing it?

Not directly but the drive doesn't spin at all and from looking at the pinot diagram it appears this pin controls MTRON which turns the motor on, hence no spinning.

BlueOwl

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#2734148 25-Jun-2021 10:53

That pin is probably supposed to be missing.

I seem to remember that pin 3 was blanked on many insulation-displacement connectors and the pin was left out on motherboard headers to act as a kind of keying mechanism to prevent the connector from being attached the wrong way.

All of the odd pins are connected to ground, so having one missing wasn't a problem.

frankv

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#2734210 25-Jun-2021 11:11

@gbwelly, I don't believe your arrow is pointing to the right connector on the reverse side? Your arrow points to holes that appear to be in a zig-zag pattern, not 2x17. I think that the tail of your arrow is pointing to the connector in question?

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