General Category > Lisa Troubleshooting and Repair

Edge Connector Replacement

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patrick:

--- Quote from: fri0701 on December 19, 2022, 11:01:21 pm ---While we're on the subject, recently I had an odd component failure in a 1.2A PSU - the transistor at CR21 "blew its top" and its case cracked in half (picture attached). I'd like to get a replacement... the schematics say this component is a "MPU131", which might be this: https://digitroncorp.com/Digitron/media/Files/Datasheets/MPU131-MPU133.pdf

--- End quote ---
This is a "programmable uni-junction transistor" (PUT). A long time obsolete device that behaves like a voltage controlled thyristor (a real thyristor or "silicon controlled rectifier" is current controlled). It has a high impedance until the gate voltage reaches a certain level and then it snaps to a low-impedance state.

PUTs were used for oscillators or, as here in this application, as comparators. Newer designs prefer to rely on the TL431A zener diode (which is not a direct replacement!).


--- Quote ---I'm not sure where to find a replacement or appropriate substitute. Anyone have any ideas?

--- End quote ---
MPU131-MPU133 can be substituted by Motorola 2N6027 or 2N6028.

fri0701:
I replaced one of my memory connectors today, and it looks like the replacement part will work well - thanks! I had a broken data line on my motherboard that I was able to patch, and now my memory problems look like they've gone away.

However, I have a new problem. The gray connector in the card bay (that connects to the drive, power switch, etc) has many pins that aren't contacting the edge of my motherboard properly. After removing the connector, I noticed several pins are very loose, and some have fallen out. Is this something I'll be able to fix, or is there a replacement that anyone's used in the past they can recommend?

sigma7:

--- Quote from: fri0701 on January 07, 2023, 06:54:10 pm ---The gray connector in the card bay (that connects to the drive, power switch, etc) has many pins that aren't contacting the edge of my motherboard properly. After removing the connector, I noticed several pins are very loose, and some have fallen out. Is this something I'll be able to fix, or is there a replacement that anyone's used in the past they can recommend?

--- End quote ---
I think you are referring to the 60 contact card-edge connector that is bolted to the chassis and has a ribbon cable on the inside that splits off to the drive, power switch etc. (It is black on the Lisas that are in view to me at the moment, but I think your description narrows it down to that one)

It seems odd that some of the contacts are loose; a picture of those may be helpful in case a repair is straightforward...

At first look, this one is a bit problematic to source. I'd describe it as a 60 contact 0.1" pitch card-edge IDC ribbon cable connector with mounting flanges.

3M made this as part #s 3666-0000 and 3666-0002 but they are no longer available (you may find some NOS somewhere).

Panduit has part number varieties similar to 055-060-455x  where x is F or S for mounting flanges (no flange if blank), but the sites I've checked don't carry it.

This might be a usable part:
"(CPC) 499559-7"  near the bottom of the page at https://www.surplussales.com/ComputerAccess/con_edge.html

Alternate ideas:

Similar parts are available without the mounting flanges. If you can determine the cause of the loose contacts, it may be possible to purchase a similar connector of the same brand and scavenge contacts from it to repair yours.

60 contact card edge connectors with flanges and wire-wrap tails are available. Using one of these with a common 60 contact IDC socket header plugged onto the wire-wrap tails should work ok. The wire-wrap tails have a row spacing of 0.2" so they would need to be bent a bit to fit the header with 0.1" spacing.

The same part without the mounting flanges might be usable by fabricating flanges and attaching them. I think this may be difficult to make strong enough but not impossible.

fri0701:
I am referring to that connector, yes. I was noticing problems with my power switch not working, keyboard having issues, etc, and narrowed it down to that connector.

To be more specific, many of the metal pins in that connector have lost their "springiness". Some have fallen completely out of the connector body, and at the end of each of these pins, there's a blue mound of corrosion. Removing the plastic back of the connector (that crimps the ribbon cables in place) revealed more blue corrosion.

I think, unfortunately, that the battery damage in this Lisa was so severe that it damaged this connector too, and the pins I'm seeing that are falling out are actually broken off, having been eaten away :(. In retrospect, this connector being unreliable explains a lot of the intermittent issues I've had with testing various boards, so I'm at least happy to have found the culprit.

For the short term, I have a spare harness from another Lisa body that I can swap in, but eventually, I'd like to find a more permanent replacement. A quick and dirty "solution", of course, would be to use any 60 pin connector that fits and to solder some ribbon cables directly to it, but I'd like to avoid that route. That link you sent seems like it would work, so maybe I'll give that a shot - thanks!

sigma7:

--- Quote from: fri0701 on January 08, 2023, 09:36:32 pm ---I think, unfortunately, that the battery damage in this Lisa was so severe that it damaged this connector too, and the pins I'm seeing that are falling out are actually broken off, having been eaten away :(

--- End quote ---
In that case, you might save the housing portions of the connector in case you need to resort to replacing the damaged contacts with new ones from a similar connector of the same brand (eg. you may be able to get the same style of connector in a different size or without flanges).

As well as checking all of the remaining connectors, also examine the wires connected to them (as corrosion will progress along the wire under the insulation) and trim back or replace as needed.

Good luck!

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