PAL 800XL with no colors

[scelbi8h]

Hi guys,

 

I got today an Atari 800XL and while everything works ok, it shows on screen a lovely black and white image (looks really sharp!). It's a PAL machine, and I'm using with this CRT TV both PAL and NTSC Ataris with no issue, so it's something coming from the computer. I'm getting the image from the composite video out - I don't have yet an S-Video cable. 

 

My first thought (and I'm positive is where the problem is located) was to turn the potentiometer on board. Well, no luck, moving it all the way to the left and right made no change, but only at the very end of it when turning it in clockwise direction. While I get some change on this position, it shows horrible looking bleeding colors. It's like if I could get the good image if only the potentiometer could go beyond this point.

 

Do you think it's a matter of a faulty potentiometer? Or maybe it got out of spec for some other reason? Otherwise the computer works great, I was even doing some BBSing in 80 columns mode - with this sharp B/W image it looked great in 80 column mode!

 

A couple of images:

 

 

Edited January 15, 2022 by scelbi8h

[_The Doctor__]

Maybe the other machines that work are modified to use s video etc and this one is just putting out chroma with some sync bleed through.

[Beeblebrox]

@scelbi8h I had this happen with an a 130XE I brought back from the dead. In my case it was the Q3 transistor that needed replacing which was causing the lack of colour aside at one small stage when turning the pot. May or may not be the same for your 800XL but sounds suspiciously similar.

 

See here: 

 

Edited January 16, 2022 by Beeblebrox

[scelbi8h]

9 hours ago, _The Doctor__ said:

Maybe the other machines that work are modified to use s video etc and this one is just putting out chroma with some sync bleed through.

But I'm not using the S-Video out, just composite.

 

9 hours ago, Beeblebrox said:

@scelbi8h I had this happen with an a 130XE I brought back from the dead. In my case it was the Q3 transistor that needed replacing which was causing the lack of colour aside at one small stage when turning the pot. May or may not be the same for your 800XL but sounds suspiciously similar.

 

See here: 

 

The content of that thread looks promising! It makes sense one of the transistors is defective, so I'm going to try that first and maybe see what happens with another 74LS74 I must have around while I get the parts. Thanks!!

 

EDIT: Just ordered a set box with some different transistors from Amazon, I should have it tomorrow. As I saw in this service manual, Q1-5 are the same as in the 130XE (2N3904) which is included in this transistor set.

 

Atari 800XL Field Service Manual (Page 28 of 30) | ManualsLib

 

Hopefully I'll have it fixed by tomorrow! I was also thinking about installing an UAV board I have around. My question is, does the UAV replaces only the IC where is mounted or some other components from the video circuit too?

Edited January 16, 2022 by scelbi8h

[_The Doctor__]

make sure you use darlington transistors, normally higher gain, more responsive, better picture

[scelbi8h]

2 hours ago, _The Doctor__ said:

make sure you use darlington transistors, normally higher gain, more responsive, better picture

Thanks for the advice. I bought a box with some different transistors, but I'm afraid they are all made in china or similar. From now on I'll be looking for the Darlington ones. Well, I hope with the new transistor (if that's the issue) and the UAV I'll get a nice image. 

Edited January 16, 2022 by scelbi8h

[_The Doctor__]

You will be very happy with the UAV!

[scelbi8h]

Solved! My Atari 800XL is not a B/W computer anymore!

 

I received this morning that transistor set, so after getting it went home and replaced Q1... just to find out the issue was somewhere else, because placing a new transistor there did nothing at all. 

 

So I started looking carefully at the board. Well, there where 2 strange resistors doing piggyback on others, another one acting as a jumper, C54 was missing and the modulator had all the cables cut. Also on the bottom, there was a jumper cable going to the chroma pin on the DIN socket. So I guess somebody did an S-Video mod and if I only had a S-Video cable I may have seen colours right away, because I suppose composite colour got disabled with this mod. I couldn't see all these things before because until now I didn't remove the RF shield.

 

I decided to undo all these modifications and installed that UAV board I had left (I purchased 3 of them a couple of months ago, and thought I would never need more... and now I'm out of UAVs!). The C54 capacitor was still missing and couldn't find a replacement, so the C54 socket was left empty. Never mind, once installed the UAV gave a beautiful colour picture. Well, not right away, because as I turned the computer ON I saw a B/W screen, but turning the pot did the trick. After some adjustments it is showing the right colours, so I consider it fixed. Only the S-Video out has to be checked (A cable is on the way), which I will connect to an HDMI monitor through a RetroTink converter. 

 

As always, I got really focused on fixing stuff and forgot to take pictures. I only have a couple from my CRT TV right after fixing the computer. But I couldn't get the phone to focus properly, nor they are showing the same colours I see with my eyes. But you can get an idea: 

 

 

 

 

I'm very pleased with the result. 

 

Thanks guys for your advice!

 

 

Edited January 17, 2022 by scelbi8h

[Beeblebrox]

9 minutes ago, scelbi8h said:

Solved! My Atari 800XL is not a B/W computer anymore!

 

I received this morning that transistor set, so after getting it went home and replaced Q1... just to find out the issue was somewhere else, because placing a new transistor there did nothing at all. 

 

So I started looking carefully at the board. Well, there where 2 strange resistors doing piggyback on others, another one acting as a jumper and C54 was missing. Also on the bottom, there was a jumper cable going to the chroma pin on the DIN socket. So I guess somebody did an S-Video mod and if I only had a S-Video cable I may have seen colours right away. I couldn't see all these things before because until now I didn't remove the RF shield.

 

I decided to remove that mod and installed that UAV board I had left (I purchased 3 of them a couple of months ago, and thought I would never need more... and now I'm out of UAVs!). The C54 capacitor was still missing and couldn't find a replacement, so the C54 socket was left empty. Never mind, once installed the UAV gave a beautiful colour picture. Well, not right away, because as I turned the computer ON I saw a B/W screen, but turning the pot did the trick. After some adjustments, it is showing the right colours, so I consider it fixed. Only the S-Video out has to be checked (A cable is on the way), which I will connect to an HDMI monitor through a RetroTink converter. 

 

As always, I got really focused on fixing stuff and forgot to take pictures. I only have a couple from my CRT TV right after fixing the computer. But I couldn't get the phone to focus properly, nor they are showing the same colours I see with my eyes. But you can get an idea: 

 

 

 

 

I'm very pleased with the result. 

 

Thanks guys for your advice!

 

 

@scelbi8h  Great. Yup it always pays to open up the machine and remove the RF shield to have a look inside first.

 

The jumper cable to DIN plug (pin 5 I think), is part of the Chroma line reconnection S-video related mod. (As you probably know for the majority of the 800XL the S-video chroma line was not connected at the factory, so S-video is always black and white until you connect it up). The C54 capacitor was removed intentionally as part of the mod also as it improves image quality with the mod if I recall. (I removed this capacitor myself in one of my 800XLs last year IIRC).

 

It may well be then like you say that the mod you had in place was one which had removed composite colour leaving only S-video. I vaguely recall a version of the mod that removes this, but the name of it escapes me, (Sure it has Super in it heh heh!).

 

Glad installing UAV has helped rectify this. I also fell for the need to readjust the pot at some stage after I'd fixed my resurrected 130XE.

 

 

 

[scelbi8h]

10 hours ago, Beeblebrox said:

@scelbi8h  Great. Yup it always pays to open up the machine and remove the RF shield to have a look inside first.

I learnt the lesson 

 

10 hours ago, Beeblebrox said:

The jumper cable to DIN plug (pin 5 I think), is part of the Chroma line reconnection S-video related mod. (As you probably know for the majority of the 800XL the S-video chroma line was not connected at the factory, so S-video is always black and white until you connect it up). The C54 capacitor was removed intentionally as part of the mod also as it improves image quality with the mod if I recall. (I removed this capacitor myself in one of my 800XLs last year IIRC).

 

It may well be then like you say that the mod you had in place was one which had removed composite colour leaving only S-video. I vaguely recall a version of the mod that removes this, but the name of it escapes me, (Sure it has Super in it heh heh!).

I got this idea somewhere. In some page or PDF I read about a mod where the C54 had to be lifted by one leg and a switch could be installed there if you wanted to use composite, because with that mod the composite colour got disabled. I've been looking for that document but I can't find it right now, so maybe I'm mistaken and it doesn't apply to C54 but another capacitor.

 

10 hours ago, scelbi8h said:

As always, I got really focused on fixing stuff and forgot to take pictures.

Quoting myself here, because I do have a picture from the board as it was before working on it, taken by the seller from eBay. A bit blurry but you can see the missing capacitor and some other modifications. (BTW, almost everything is socketed!)

 

 

Zooming in, here you can see in the circle a resistor making a bridge, and pointed with arrows the missing capacitor and a resistor installed over another. There was another resistor like this, but I can't locate it now. There's no picture from the other side of the board.

 

 

And now for some pictures from before...

 

 

...and after. It had a weird uneven yellowing on the white part of the case, but a deep cleaning and a couple of mornings in this winter sun left it like this. 

 

 

Very nice one, with an Alps switches keyboard. The keys have no signs of use on the surface (function keys even still have the protective plastic layer), and it's a pleasure to use it. By the way, I have other two 800XLs, a 600XL and an 800 and none of them have the mylar keyboard. So far I never saw one, I thought it was common to get an Atari computer with the mylar keyboard, or maybe I was just lucky.

 

I was thinking about selling this computer after fixing it... But on a second thought I feel I want to keep it. ?

Edited January 18, 2022 by scelbi8h