hw keyboard failure

Page 1/3
| 2 | 3

By PingPong

Prophet (4093)

PingPong's picture

27-09-2012, 16:15

Hi, i've discovered that my old msx1 sony hb 10p has a failure detecting keypress on some keys.
for example 'b','r','7',';' does not detect keypress.
i suspect is a failure in some column / row hw line or worse, a problem in PPI ?
anyone know if those keys share a common row or column?

i've discovered that there is an approximate n. of keys not working. the rate is 1 key dead every 8 keys.

Login or register to post comments

By hap

Paragon (2042)

hap's picture

27-09-2012, 16:27

PPI chip should be fine, otherwise it probably wouldn't even boot up Tongue but test PB7 to be certain about it: http://www.thesatya.com/images/pin8255.png
Check the keyboard matrix here, http://map.grauw.nl/articles/keymatrix.php you can see they're all on the same column, right?

*edit* typo :O

By PingPong

Prophet (4093)

PingPong's picture

27-09-2012, 18:09

hap wrote:

Check the keyboard matrix here, http://map.grauw.nl/articles/keymatrix.php you can see they're all on the same column, right?

hi hap. i've an international keyboard, checking to the matrix should be bit 7 that is not working.
However, i'm confused: in the case of bit 7 the dead keys should be more.
the return key and right cursor key works fine on my machine, they should not work if bit 7 is broken.
any idea?

By jltursan

Prophet (2619)

jltursan's picture

27-09-2012, 18:24

Have you got some keypresses varying pressure?, are they absolutely dead?, most of the time it's only a mechanical failure: cold solder joints, dirty conductive plates, degraded contact rubber cups. Usually I find all of them; but your failing keys are in the same column; so at a first look can be suspicious.
Anyway you'll need to dismantle the keyboard, using a voltmeter you can easily check the continuity failures.
I've never seer a faulty 8255 tho oO

By PingPong

Prophet (4093)

PingPong's picture

27-09-2012, 18:30

jltursan wrote:

I've never seer a faulty 8255 tho oO

it's suspicious, i've never tryed more deeply,my machine is a HB-10P SONY and i've not found somewhere instructions for accessing the keyboard by dismounting the unit. because my pratical skills are the worse one can imagine i'm also afraid to break something.
apparently the dead keys does not work even if strongly pressed
Crying is this the end of my msx?

By PingPong

Prophet (4093)

PingPong's picture

27-09-2012, 20:09

update:
dismounted the machine. here my considerations:
- machine is clean, no sign of dust, oxide, no dirty internals
- the flat cable connections with keyboard appear to be intact and clean.
- i've looked for the PPI, but i've found a thing that shocked me. this machine has a S3527 inside, i guess the PPI is here. there is also the infamous vdp clone by toshiba.
- all keys with bit 7 are DEAD except return and right cursor keys that are probably connected elsewhere

the keyboard flat cable has 24 conductors. anyone knows about the meaning of signals?

anyone can help me in finding what's wrong?

By OeiOeiVogeltje

Paragon (1426)

OeiOeiVogeltje's picture

27-09-2012, 21:04

a cut line on keyboard film? (if any)

By PingPong

Prophet (4093)

PingPong's picture

28-09-2012, 01:45

i think there is no interruption. i need to find a way to easily blame the S3527 which i suspect may be the problem. maybe pin x7?
however i do not know how to do to know if it's the S3527 or not

By sd_snatcher

Prophet (3642)

sd_snatcher's picture

28-09-2012, 03:27

@PingPong

It may be:

1) A problem on the signal path to/on the keyboard. Check all the soldering and connections. Check if there isn't any ruptured track on the machine mobo. Check the keyboard film. Check all the signal path with a multimeter.
2) Dead pin on the S3527

On the first case your machine can be easily fixed. Just fix the problem on the signal path.

On the second case, you probably can kiss your machine goodbye, because (a) it's very hard to find a replacement S3527 and (b) it's very hard to do the actual replacement, as it requires wild soldering skills. The problem could be easily fixable, if people actually respected the standard, by plugging a cartridge with a new keyboard interface and replacing the BIOS, or even by using Danjovic's cheap PS/2->joystick port adapter and a modified BIOS. But sadly, it seems very hard to convince people of the many advantages of respecting the standard coding guidelines, making upgrades and alternative fixes very hard/expensive.

By hit9918

Prophet (2927)

hit9918's picture

28-09-2012, 14:13

"all keys with bit 7 are DEAD except return and right cursor keys that are probably connected elsewhere"

Looking at a layout diagram,
return and cursor is Y7 Y8 of X7.
Maybe some wire broken between Y7 and Y6 of X7, not PPI X7 broken?

On Y6 is F3, how about that one, do the function keys all work.

By PingPong

Prophet (4093)

PingPong's picture

28-09-2012, 21:18

hit9918 wrote:

"all keys with bit 7 are DEAD except return and right cursor keys that are probably connected elsewhere"

Looking at a layout diagram,
return and cursor is Y7 Y8 of X7.
Maybe some wire broken between Y7 and Y6 of X7, not PPI X7 broken?

On Y6 is F3, how about that one, do the function keys all work.

@hit9918: all keys means all keys unfortunately: so f3 key is also DEAD.

My problem: I need a way to first check the integrity of S3527. If this chip is ok, i can research more deeply the problem, that probably is fixable, otherwise no hope. Sad

Page 1/3
| 2 | 3