Video problem on Toshiba HX-20

Rookie (23)

14-09-2004, 08:46

Hi to all,

I'm new to this forum, but I own an MSX from the '86

Recently I bought a 2nd hand Toshiba HX-20, with a little problem.
I connect the MSX, power on it, it works, but after some minutes the top of the screen starts to change color (a strange dark green).
(for ex. in MSX-Basic, screen totally blue, the top becomes "strange green" and the rest blue).

The "strange" color starts to invade the screen from the top to the bottom, but very slowly.
The screen becomes all so, and a few minutes after, it becomes totally black&white. (color disappears totally).

I tried to get the video-signal from both composite output & RF output, but the problem is always present.

I thinked that some component malfunction when it heats.
I opened the Toshiba and I tried to heat gently the PCB over the motherboard (the one which outputs video/audio and RF signals), but nothing.
Then I thinked the damage is around the VDP.
I suppose the damage is on the top of the T6950, where are 2 capacitors, an oscillator (quartz) and a variable capacitor (I think!).

Someone may help me?

I appreciate every reply.

P.S.
Anybody could tell me where to download the service manual for Toshiba HX-20 (HX-10 & 22 too)?
I searched for days on the net, but nothing to do!

By anonymous

incognito ergo sum (116)

14-09-2004, 15:35

I suppose the analog circuitry that composes the video signal is breaking down. The VDP is probably ok.

By davcl

Rookie (23)

14-09-2004, 20:33

Hi GuyveR800, thank you for reply!

The T6950 is different from standard MSX1 VDP (TMS9929), as it has more pins.

I noted that the PAL-Encoder (LVA510) lacks, so I think T6950 outputs directly PAL-video signal.
Is it right?

Please, someone has idea on how to fix this problem?

Someone has the pdf of T6950?

By Manuel

Ascended (19300)

14-09-2004, 20:45

The HX-20 and HX-22 are very rare, at least in the Netherlands and the rest of Europe, as far as I know...

By flyguille

Prophet (3031)

14-09-2004, 21:26

all msx has an analog circuit that modulates the colour signal... then send the signal to the mixer for finally go out by the video plug

if the msx was a lot of time in the closet, maybe it just get humidity not much as notice it, but maybe that is happening

get a air-hot-machine , then dry hotting a bit the board.... just a bit

then , ensamble all , and test

other thing can be the calibration of a coil. or maybe your TV is not capable of show correctly the unacurate signal that makes a msx... , sometimes happened to me, try test it in other tv set.

By anonymous

incognito ergo sum (116)

14-09-2004, 21:32

Frankly, I have never heard of a T6950 VDP... Who is the manufacturer?

By dhau

Paragon (1570)

15-09-2004, 03:24

davcl, just get another computer and dispose of this one. It will be cheaper. Unless it is a fun project for you

By davcl

Rookie (23)

15-09-2004, 08:34

Frankly, I have never heard of a T6950 VDP... Who is the manufacturer?

T= Toshiba!

By davcl

Rookie (23)

15-09-2004, 08:43

davcl, just get another computer and dispose of this one. It will be cheaper. Unless it is a fun project for you

I've got my old Philips VG8020 (my first computer!) in working condition, but HX-20 is very RARE in Italy.
And... I want it perfect functionally! I think a "stupid" component is damaged.
I'' try to make some other tests on the PCB...

By anonymous

incognito ergo sum (116)

15-09-2004, 13:08

Frankly, I have never heard of a T6950 VDP... Who is the manufacturer?
T= Toshiba!
Could've known that, but wanted to be sure anyway... It's logical tho. Their MSX-ENGINE chips have a T69xx number too.

By davcl

Rookie (23)

15-09-2004, 19:29

Hi boys,

I think I fixed the problem.
Just I did a "fine tuning" of the variable capacitor on the top of the VDP.
The HX-20 seems to work ok (from 40 minutes).

However, I'll wait more, befor exulting

P.S.

On the VDP I read:

Toshiba
T6950
JAPAN8519Y