HP 9826A key switches



#5

I've come into possession of a 9826A controller, the red-headed stepchild of HP collectors.

It was free, and has 2.7MB of memory.

I installed a TAS-obtained BASIC 2.0 card. It took me a while to figure out how to use it, 'cause the manual says with a ROM BASIC card it will simply come up automatically and say READY, but in reality it displays "ROM: B B" at the upper right hand corner of the screen and you have to press "B". But I digress...

Several of the keys on the keyboard don't register. Checking with a multimeter, I can see that pressing a working key shorts the corresponding switch's two contacts on the bottom of the keyboard PCB, whereas pressing a non-working key does not. OK, so the problem is the key switch.

The dead keys are really dead and will not register no matter how hard I bang on them.

Physically, the 9826A key switches look very like modern key switches. They snap into a metal support plate and have two solder points on the keyboard PCB.

So: any suggestions as to my options? Is removing a key switch and trying to disassemble and clean it reasonable? Should I look for a parts machine?


#6

Ah, never mind. The solution is:

1. Unsolder and remove key switch. Professional desoldering station is a help, but a standard iron and pump type solder sucker can get it done.

2. Disassemble key switch. Surprisingly easy to do.

3. Remove metal switch contact plates. Wipe on T-shirt.

4. Snap switch back together and check for proper operation.

5. Repeat until done.


#7

I am pretty sure I totally dismantled one of these keyboards (perhaps on a 9836, it's the same part). As you said, it's not hard, and I found a normal soldering iron and solder sucker was easily good enough.

One thing I did was to sort the keyswitches into working and not working when I took them out. I cleaned up the not-working ones and they seemed OK, but when I put it back together, I put the non-working ones in little-used places (I almost never use the numeric keypad, so the cleaned ones ended up there).


#8

I'm sufficiently unskilled with a soldering iron and sucker to worry about lifting traces or otherwise damaging the keyboard. I did remove, disassemble, and clean the four switches on the main keyboard that weren't working (A,H,J, and X) and they're all back in now. There are five more nonfunctional switches on the numeric pad and I just noticed the "6" key on the main keyboard doesn't work, but I'm going to wait until I get my desoldering station (reasonably cheap these days) to do any more work.

The machine has 2.7MB of memory but no language cards when I received it. I found the BASIC 2.0 card in California and the HPL card in Israel, both are now installed and working perfectly, although the manual's description of how the language cards work is nothing like my system. The manual says with just the BASIC card installed, the system will come up with BASIC READY, and that with both cards installed it'll say WHICH SYSTEM? B H

Mine says ROM: B H at the upper right of the screen with both cards, and ROM: B with only the BASIC card. But pressing B or H still works.

Disks format and I can save and load files with no problem.

Oddly, the machine identifies itself as a 9836A when it boots. Perhaps this is the result of a service or parts swap?


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