HP-97 keyboard problem

[Dave92F1]

I just got my 3rd HP-97 from eBay. Two rows on the keyboard don't seem to register.

The digits 1, 2, 3 and the whole row ENTER/CHS/EEX/divide do nothing at all when I press them.

Other than that the calculator seems OK (didn't test the printer or card reader yet; I suppose they'll need the usual...)

I already completely disassembled and cleaned the keyboard and key contacts - that didn't help (didn't make it worse either). I also checked the connection on the pins in connectors P1 and P2 carefully - that doesn't seem to be it either. I tested with a known-good battery pack and charger from another HP-97.

Any suggestions?

If I can't get it working, I'll have to sell it for parts and buy another one (I actually use these things!)

[Paul Berger (Canada)]

Well most of the keys you mention are in the same column, what about DSP, A, B, D, E, RCL and f? also in the same column. If all the keys in a column don't work they are driven by the PIK chip the divide key seems to be in a different column, but in the row with CHS - and FIX, the rows are driven by the cathode driver, and if one of them is bad you should be missing a digit in the display as well. If some but not all in a column do not function I would look for a broken connection on the keyboard.The service guide, available on the MoHPC documentation memory stick, shows a grid of the keyboard wiring.

Paul.

[Dave92F1]

[Edited to correct stupidities...I am not always the sharpest tool in the shed.]

Hm. I checked again. Here's the complete list of keys that don't respond:

A B C D E f RCL DSP CLX ENTER 1 2 3 EEX CHS

The FIX and divide keys work OK.

So, you're right - it's the whole rightmost column in the schematic on page 4-23 of the service manual. Which looks like it connects to pin 1 of connector P1.

Do I have a bad cathode driver chip (U1) ? Is that something that can be replaced (I'm up for desoldering/resoldering a 22 pin DIP)? Or is it made of unobtanium?

Or - is it perhaps the mess of transistors and diodes in the lower right corner of page 4-15 (the logic board schematic). That seems to show Pins 1 and 2 of P1 both connected to C6 - if so, why is only the rightmost column affected (and not the one next to it?)

[Paul Berger (Canada)]

No if it is column that is out it's not a bad cathode driver, they drive the rows, the columns are driven by the PIK chip and if it is truly bad the only place to get another is from another topcat, the same applies for the cathode driver it is also a custom chip but in the case of a failed cathode driver there are alternatives to get them to work, but would involve modification. I have not verified this however my guess is that when a key is pressed, it pulls down the column line under it when the cathode driver for the row is active.

For your missing column check carefully between the KBA pin on the PIK (looks like pin 24) and the first key contact you will need to trace from the P1 connector to the pad on the keyboard the actual wiring likely does not look like a nice grid. Check right from the actual pin on the chip as it could be a cold solder joint. If the connections are good I am afraid it is likely a PIK chip. Do all of the voltages inside look good? Its a long shot but if one is marginal they can do some weird things.

[Dave92F1]

Thanks. The connections look good all the way to the gold traces on the keyboard PCB.

I'll check the voltages tomorrow, but probably it's the PIK. Sigh.

Eventually I'll post it for parts on eBay; I'll post a link to the auction in case somebody here is interested.

Other than that one problem, it's a good looking calculator (esp. after I spend several hours today cleaning it...).

[rprosperi]

(02-19-2016 11:04 PM)Dave92F1 Wrote:  Thanks. The connections look good all the way to the gold traces on the keyboard PCB.

I'll check the voltages tomorrow, but probably it's the PIK. Sigh.

Eventually I'll post it for parts on eBay; I'll post a link to the auction in case somebody here is interested.

Other than that one problem, it's a good looking calculator (esp. after I spend several hours today cleaning it...).

Dave - Forum rules prohibit posting links to items you are selling yourself, to avoid the obvious explosion of posts that would otherwise result...

But I suggest you post a note in the Forum classified section to allow MoHPC members to contact you directly to purchase (or trade, etc.) prior to listing it on TAS. Listing fees are cheaper here as well.

[Dave92F1]

Thanks, Bob - will do. (Didn't mean to break any rules.)

It will be a few weeks (I'll keep it for parts in case the next one I get has a problem... once that's settled I'll offer it for sale - all flaws described, of course.)