C128 display problems

[diskers]

Hi everyone,

I have a strange problem with one of the C128. For exemple in Ikari Warriors or IK+ the backgrounds that should be black are white (in Ikari warriors the main screen with the two soldiers is white as well as ingame backround and in IK+ the background have white squares instead of black as well as on player "sahdow"). Anyone could know what it can be?

Cheers,
diskers

 

[r0jaws]

How are you connecting to your video output? RF, Composite, VGA?

 

[diskers]

DIN to SCART connection. I'll will pack some pics taken from the tv and post them here.
PS. Here's the link to 4 jpg taken with my phone from TV:
http://www.filedropper.com/c128screenpics

 

[diskers]

PS. I will connect the c128 using a RF cable and see if the same problem persist...

 

[diskers]

Hi again,
OK the same error occurs in bith DIN and RF connection. Any clue?

 

[roy_bates]

any chance you can post the picture here in the thread?

 

[diskers]

Here we go:

 

[r0jaws]

Have you tested the power supply, Is it putting out the correct voltages?

Also, the removable chips on the main board. I had some graphical problems with my 128, not exactly the same as this but garbled graphics. I had to remove, clean with compressed air and isopropyl all the chips and sockets. Systematically working and testing them I narrowed it down to the ROMs. I advocate carefully removing the Chips altogether, cleaning the legs and sockets before re-seating. I have far more success with that than I ever have by just pressing down on them.

I now have JiffyDOS installed and have had no further problems.

 

[diskers]

Hi again,

I tested briefly the PSU and... the 9VAC is only 7VAC on the pinout side but on the PSU direct out it's 10.5 VAC..... The 5.0V seems to be OK at pinout side and aswell at PSU out (5.05).

 

[r0jaws]

Where are you measuring the 7v at? Do you have another PSU you can test with?

 

[diskers]

Hi,
The 7VAC is on the PSU connector (if I remember well pins 3 and 5). No I have only one PSU for the amiga style case C128.

Cheers,
diskers

 

[r0jaws]

You should have 9v. I believe the 9v isn't extensively used so maybe a read herring. but it's one thing that would need to be ruled out.
I had a look last night and it looks like the 9v is used by the CIA and SID chips, and serial port. It may also have something to do with the video output frequency. At the moment my money would be on that. Especially if you are testing it on the other side of the PSU input and it's losing 3v.

Also, have you cleaned and reset any of the chips? Is the condition of the board ok? No bulging caps or anything?

 

[roy_bates]

its not just a case of you having the contrast turned up too far is it?
yeah does sound silly.

 

[diskers]

@roy_bates no, the c64, amigas, snes and megadrive work fine...
@rOjaws I opened before the c128 and took off the chips then reinserted them. I didn't saw any leaking caps or any damage on the mobo. Anyway I will try to find some time to open it again and clean the pins and sockets (but a waste of 2V is I think the cause). As I presume the inside 9VAC must be rectified to 9VDC on the mobo for the ICs that use this voltage , so a converter from AC to DC is another loss of about 0,5V....
Anyway I also have a problem with a 1571 internal drive in a 128D...LOL...but it will be for another thread...

 

[roy_bates]

your probably going to think,huh whats he talking about.but here goes.
that 9 volts ac gets rectified and converted to 12 volts dc through a regulator in places.

 

[diskers]

LOL...Those Commodore engineers must be really frightened by the Jack Attack.....9VAC===>9VDC===>12VDC . Anyway if a rectifier/converter doesn't receive enough juice it won't give a stable current....

 

[xc8]

I am curious how this C128 boots, AFAIK the z80 needs 9v ...
VIC needs some checking anyway.

 

[roy_bates]

well you was close,9VAC to 12VDC,no 9 volts dc in the middle.


a bit off topic but,you can turn 12 volts dc into 240volts and upwards, the tech has been around long before these machines etc

 

[diskers]

It would be so much easier to make a direct 12VDC and the PSU would be smaller....

 

[roy_bates]

It would be so much easier to make a direct 12VDC and the PSU would be smaller....

its not really true,if it was just 12 volts you would still have to find the other voltages from it,so the 12 volt line would have to be alot more stronger to compinsate for the draw on power comming from a single line.