CDTV keyboard issues

[hishamk]

I have a CDTV with a keyboard that I haven't gotten around to use until now. I found out that the 5 pin DIN connector had a broken pin so I decided to replace it.

I've attempted to replace the connector with a modified ps/2 connector (twisted out the 6th pin and snapped the plastic key bit).

Right now it's a bit of a hacky job with temporary splice connectors to see if it works. I've done the following connections (see attached diagram):

C12 connector on keyboard circuit:
RED - GROUND
WHITE - DATA
YELLOW - CLOCK
ORANGE - +5v
Case Ground -> Connector Shield Ground

So on power up, the keyboard's caps lock key blinks once as usual. However, once it gets to AmigaDOS a constant stream of apostrophes is typed (raw code 00) (no, that key is not stuck - even if it was, I would still be able to type other characters). Pressing keys on the keyboard does not do anything, including the reset combo. Pressing caps lock works (light on/off) but then after five presses or so it stop to light up. The '`' stream continues indefinitely nevertheless.

To test whether the keyboard actually works and that the MCU is not fried, I tested it with my A3000 (I just swapped in the cable from the A3000's keyboard). It worked fine on the A3000.

I also decided to try the A3000's keyboard on the CDTV with my hack cable and the result was the same as with the CDTV keyboard, a series of never ending '`', and no other keys responding, including reset combo.

So this tells me the keyboard is fine. It's something else that's gone amiss.

I swapped around the CDTV's odd and even CIAs and that didn't make a difference.

So I'm beginning to guess that either my hacky connection is wonky or that it's something between the keyboard port and the CIAs that's causing an issue.

Would it be worth replacing both CIAs with completely new ones? I've got a few donor machines I could pull those out from. FWIW I've tested the CIAs with Amiga Test Kit and everything passes.

Does anyone have any suggestions on what could be wrong?


Thanks

[hishamk]

I did try them swapped, but then there’s nothing at all, not even the apostrophe.

Tested both ends of cable for shorts and continuity and it all checks out.

[hishamk]

Thanks @Pat the Cat for the help so far.

I just tried it with the keyboard sense grounded but it's still the same infinite apostrophes.

[hishamk]

No, it was pretty much what I had.

I've also checked continuity across the port, keyboard SSM and CIA and both data and clock pins seem to be fine.

My issue seems very close to this one: http://eab.abime.net/showthread.php?t=94188 - he even got the apostrophes

He seems to have resolved it with a beefier PSU.

[hishamk]

I measured the voltage going through the keyboard and it's at 4.65v. Not sure if this is off 5v enough to cause issues though.

[hishamk]

Well, I measured the voltage between the port Vcc/GND pins and it's 4.99v. I've also linked the keyboard with a much shorter cable and the voltage is at 4.99v on the keyboard's mobo.

I've measured continuity across the port, 252609-02 chip, and CIA. Data and clock lines are fine.

I switched the CIAs, swapped in a different Gary and it's still the same. The apostrophes persist. All tests done with an extremely short connection at 4.99v.

The only thing left is to swap in a new 252609-02.

Not sure if there are any other things I could check. I have an old oscilloscope that I could pull out and peek at signals, but need some help as to what exactly to look for.

[hishamk]

It looks like it's RP6. The resistance is pretty shot for 40 and 39 against +5V. It's around 2 ohm.

I didn't do the oscope check since I was concerned about grounding (I have an old Tektronix analog scope and the CDTV appears to be earth grounded - not an expert on these things though).

I have individual 10k ohm resistors. I was wondering if there's a way to hack them temporarily on to the connections to see if that'll fix things before replacing RP6 outright. Possible?

In any case, I've sourced a 10-ohm 10-pin pack but it might take a week or so to get here.

Cheers

[hishamk]

So I replaced the 10k resistor pack and also the 10uf 50v cap by the keyboard port (the old one was fine though). Still no joy, exactly the same behavior.