Image of inside of HP71B HP-IL module

[pamphonica]

I have a pretty clearly damaged HP-IL module and would like to see what the contact area should look like. If anyone has a working 82401A HP-IL module and would be prepared to lift off the metal cover and take a few close-up photos I would be very grateful indeed. I think there may have been small metal fingers on the pads, but all that is left is a roughened solder surface, and two pads are missing but have no obvious traces to them. The main calculator just has a set of flat edge-connector-style pads.
My module does not appear to the host HP71B so there is almost certainly a contact problem, at the very least.
It seems a real shame to just junk this module as it might be persuaded to work again.
All help gladly received.
Jeremy

[Dave Frederickson]

From the HP 71B Compendium.

[Sylvain Cote]

Beware, there are two pins that are missing from my module picture.
I still need to find time to solder them to make the module work again.

[J-F Garnier]

From one of my HP-IL module:



Can you post pictures of your damaged module?

J-F

[mfleming]

This image from the Hardware Design Spec may help visualize replacement contact fingers.
   

The fingers look to be about 10 mil thick (0.010", 0.25mm) phosphor bronze that you may be able to fashion for yourself from sheet. Another possibility might be half-round jewelry wire of the right gauge. Anything that makes contact will do, since you're unlikely to remove the module once it works!

[pamphonica]

That's enormously helpful. ALL the fingers on my module are missing! And two pads are damaged, and one pad is lifted (not obvious in photo).
I'll need to do some very fine soldering to replace them. Phosphor Bronze is probably a good idea.
It's interesting that this module came IN an HP71B, but the fingers were nowhere to be seen, so the seller must have known it was bust. I got a large rebate!
Photo attached.
Thanks everyone,
-Jeremy

[J-F Garnier]

I can't believe that the contacts have been accidentally damaged. It seems to me that they have been deliberately removed. For what purpose? Not to wire the module inside the HP-71B case, as can be done with RAM or ROM, because it would not fit due to the HP-IL connector.
Maybe have they been reused to repair another module.
In the same way, you may try to find a cheap module like a low-value 4K RAM to get replacement contacts. Soldering them in the right position may be tricky.

J-F

[pamphonica]

I agree - they seem to have been removed, maybe to repair something else. Of course this module may well prove to be dead when I put the new fingers on!

There are differences in shape (bending) between your excellent photo above and the technical design drawing. But I can see what shape the contacts have to take, and I expect I can replicate that. I have found some 0.4mm phosphor bronze rods on Ebay that look promising. I will probably have to make up a jig to keep the rods in place while soldering them.

But that's a job for another day. Meanwhile, I hope that a working module will soon be on its way to me. Then I can check things out in the HP71B

[Dave Frederickson]

When soldering module pins it's helpful to tape them all together to maintain alignment.

https://photos.google.com/album/AF1QipO_...A7-yz1dRz4

The tape in the pic is relatively antistatic however do NOT use regular cellophane tape.

[cruff]

(08-03-2020 08:23 PM)Dave Frederickson Wrote:  The tape in the pic is relatively antistatic however do NOT use regular cellophane tape.

I get a 404 error when I try to view the picture.

[rprosperi]

Same here. It appears the file was not set to public, as gDrive forces me to sign-in, and then fails with 404.

[Dave Frederickson]

Here it is.

https://drive.google.com/file/d/1FitAQXc...sp=sharing

This also protects the pin contact area from getting tinned by accidental bumps from the soldering iron.

[pamphonica]

Very good suggestion - it looks like Kapton tape. Excellent stuff for high-temperature work. I was thinking of a tiny bakelite jig with holes but this may well be easier and better.
Thanks

[J-F Garnier]

(08-04-2020 04:42 PM)Dave Frederickson Wrote:  https://drive.google.com/file/d/1FitAQXc...sp=sharing
This also protects the pin contact area from getting tinned by accidental bumps from the soldering iron.

This one looks like a 4K RAM module.
So, Dave, it seems you did remove/replace module contacts, was it to repair a module?

J-F

[Dave Frederickson]

(08-05-2020 12:50 PM)J-F Garnier Wrote:  

(08-04-2020 04:42 PM)Dave Frederickson Wrote:  https://drive.google.com/file/d/1FitAQXc...sp=sharing
This also protects the pin contact area from getting tinned by accidental bumps from the soldering iron.

This one looks like a 4K RAM module.
So, Dave, it seems you did remove/replace module contacts, was it to repair a module?

J-F

No. I was making an "OD module" for a FRAM71 module.

(08-05-2020 09:18 AM)pamphonica Wrote:  Very good suggestion - it looks like Kapton tape.

Correct.

Dave

[pamphonica]

Ah, the legendary FRAM71 module! Looks like I came just too late to the party for one of those... It's a shame, as I do intend to actually use my HP71B to control testgear etc, so it would have come in useful.
If anyone reading this has one to sell do contact me.
-Jeremy

[pamphonica]

I finally got the module under a microscope so I could work on it.
With my finest soldering tip I touched each pad and confirmed that the pads were intact (except 2 that I can see are damaged). Then I found that the plate-through holes still had the tips of the contact fingers in them. So someone virtually wrenched off the fingers. That sounds more like gold harvesting than salvaging the fingers.
Anyway, the only way to remove these was to flip the board and get a soldering iron and finest tweezers onto the underside, to grab the remainder of the leg, very fiddly even under a microscope.
Finally I got the desoldering gun with finest tip onto the underside and cleared out each hole. No further damage other than a partial floating pad on the topside which has been heated and is now flat again.
Here are photos of the pads. Underside with the first three finger remnants removed, topside with all holes cleared.
Next job is to fabricate 13 fingers, and make a jig to hold them while soldering.
-Jeremy
   
   

[J-F Garnier]

Nice cleaning job!

The two damaged pads #10 and #11, with no track from them are unused by the HP-IL module. You may not need to put a finder on them.

The other pads are used (of course), including pad #9 that is named OD in the HIDS but is actually used for Dout to chain the HP-IL modules in the dual HP-IL module carrier HP82402A.

J-F

[pamphonica]

A dull morning, so I thought I should get on with the repair. I'd been putting it off since bending 13 minute springs was going to be very fiddly.
But it worked! Read on if you are interested in the details.

1. Get 4mm phosphor bronze wire(s) from Ebay. about £3.
2. Make a sacrificial alignment jig from scrap plasticard. This fits over pcb components to give a solid surface for supporting the fingers as I solder them.
          
3. Using a fine soldering iron, press scrap bit of wire lightly into edge of jig, exactly in line with each hole, leaving a groove.
      
4. bend end of wire at right agle, to fit into pcb hole, and then a slight uplift angle to raise the fingers a bit.
5. Put bent end of wire into hole and using a soldering iron press other end into jig slot enough to secure it.
6. Solder lower end carefully.
      
7. Repeat above for all 13 wires.
      
8. Cut wires to correct length (careful examination of original) and discard jig and scrap wires.
9. Turn over end of each wire to form a bent contact area.
10. carefully bend all wires down to correct angle then check that all spacings are still correct.
11. Do a quick continuity check between contacts. Only the end two should be shorted.
    

That's pretty much it. The module slide in nicely (better than the original!) and power up was slightly slower, as it should be.
I connected a loop if HPIL cable, then did RESET IO (no result as expected), then RESTORE IO which gave no result unless the loop was disconnected.
So, as far as I can tell I now have a working module.

Thank you everyone for your incredible help with photos, advice and encouragement. I'm sure very few will have to follow this route, but it is quite do-able.

-Jeremy

[pamphonica]

Cutting the wires to length:
   
Bending the wire tips
   
Correct loop fail message means it's all working!
   

Jeremy