Atari 400 (PAL) Black & White Display?

[BeaglzNZ]

Needing some help before I reach for a bigger hammer!

 

I have an Atari 400-U (PAL version) and I can only seem to achieve a black & white output. The UHF signal isn't great so I installed a UAV chip to give composite output. This gave a fantastic crisp screen but still in B&W.

 

I have double checked that the CPU board has the PAL GTIA as well as PAL CPU which it does. Also tried the 'pot' adjustment on the CPU board which didn't change things.

 

I have tried a CPU board (PAL) from a working Atari 800 and still get B&W screen.

 

I am suspecting something on the motherboard maybe the problem but not sure what - any ideas?

[erichenneke]

Are you sure it isn't the monitor you are hooking it up to? If I hook up my pal machine to a TV that only does ntsc it gives a super crisp b&w display, but no color.

[Rybags]

The colour generation crystal is on the CPU card so trying another one rules out a bunch of possibilities.

 

Some of the later stage video generation is on the power supply board so it could be the problem.

Not sure what UAV bypasses so that could rule out further possible causes.

 

But if you have a PS board from another 800 it might be worth a shot.

Edited December 30, 2017 by Rybags

[+tf_hh]

I have an Atari 400-U (PAL version) and I can only seem to achieve a black & white output.

I have double checked that the CPU board has the PAL GTIA as well as PAL CPU which it does. Also tried the 'pot' adjustment on the CPU board which didn't change things.

I have tried a CPU board (PAL) from a working Atari 800 and still get B&W screen.

I am suspecting something on the motherboard maybe the problem but not sure what - any ideas?

 

Maybe one of the pre-owner changed some parts... sometimes this happen to machines sold, brought and sold again via eBay, Craigslist and similar.

 

Take a closer look to the mainboard. The master clock crystal is located at the left side of the mainboard (pointing the joystick ports to you). This one have the frequency and/or the ATARI partnumber as a marking. When there´s a NTSC system crystal, the system will run perfectly, but you never will get a colored screen using PAL.

 

CO12285 or CO16112 = 3.5468 MHz = PAL

CO10177 or CO61090 = 3.57945 MHz = NTSC

 

So if you found a "NTSC" crystal, then you know why no color appears.

 

Do a second look (not dependent for color display, but a good indicator for "swapped parts" system) to the O.S. ROMs. These are the three 24 pin chips at the bottom of the PCB.

 

The CO12399B (socket A105) is the MATH-Pack ROM. It´s always the same (NTSC or PAL).

 

CO15199 and CO15299 is the one and only existing ROM version of OS "A" for PAL series. Any "real" PAL system should have this both ROMs. IMHO the OS "B" for PAL is vaporware. Until today nobody found it.

 

The markings for the NTSC OS are CO12499 and CO14599 (OS "A"), the OS "B" ones have a "B" after the numbers.

 

You can use the OS "B" NTSC also for a PAL system. It works fine. The only difference is a little faster tape speed (when writing to tape), reading no problems. And the key repeat rare is much faster than on PAL, but it´s usable. SIO printers MAYBE won´t work, but... I´m sure the most users can live with that

 

Good luck, Jurgen

[BeaglzNZ]

 

Maybe one of the pre-owner changed some parts... sometimes this happen to machines sold, brought and sold again via eBay, Craigslist and similar.

 

Take a closer look to the mainboard. The master clock crystal is located at the left side of the mainboard (pointing the joystick ports to you). This one have the frequency and/or the ATARI partnumber as a marking. When there´s a NTSC system crystal, the system will run perfectly, but you never will get a colored screen using PAL.

 

CO12285 or CO16112 = 3.5468 MHz = PAL

CO10177 or CO61090 = 3.57945 MHz = NTSC

 

So if you found a "NTSC" crystal, then you know why no color appears.

 

Do a second look (not dependent for color display, but a good indicator for "swapped parts" system) to the O.S. ROMs. These are the three 24 pin chips at the bottom of the PCB.

 

The CO12399B (socket A105) is the MATH-Pack ROM. It´s always the same (NTSC or PAL).

 

CO15199 and CO15299 is the one and only existing ROM version of OS "A" for PAL series. Any "real" PAL system should have this both ROMs. IMHO the OS "B" for PAL is vaporware. Until today nobody found it.

 

The markings for the NTSC OS are CO12499 and CO14599 (OS "A"), the OS "B" ones have a "B" after the numbers.

 

You can use the OS "B" NTSC also for a PAL system. It works fine. The only difference is a little faster tape speed (when writing to tape), reading no problems. And the key repeat rare is much faster than on PAL, but it´s usable. SIO printers MAYBE won´t work, but... I´m sure the most users can live with that

 

Good luck, Jurgen

 

Thanks for the above info - has helped clear up a few things for me.

 

Turns out the replacement MB I received was indeed a NTSC board which explains the B&W screen. Does mean the CPU board and memory boards are functioning fine.

 

Went back to the original PAL MB I still have and that just gives me a RED screen on boot up. Not much documentation on that issue and given the CPU board is fine it probably means the ROM chips or PIA need replacing. Probably easier to track down a new PAL motherboard - would the PSU board have any impact?

[BeaglzNZ]

Tracked the issue down to the ROM chips. Swapped the ROMs form the NTSC board as they were 'B' versions and everything is running fine. Just finished installed the RCA sockets on the back of the case for the UAV mod and took the audio from R160 and it is giving a fantastic picture and good sound. A good way to sign off 2017 - now time to crack open a beer and bring in 2018 which is less than 8 hours away!