Help diagnosing 800XL issues

[Sardonyx]

I just recently picked up an 800XL that was listed for parts.  It was inexpensive and came with some other things I was interested in purchasing that bought individually cost about what I paid for the lot.

 

The case is missing all the screws, but the plastic is like new and keyboard also looked amazing.  I figured worst case I get a spare case and some keycaps. 

 

It arrived a couple days ago and aside from all the screws being removed looks new.  I figured I may as well fire it up and see what state it's in.  To my surprise it actually powered up to BASIC.  However, it was in black and white.  I tried the onboard self tests and the audio/video tests were fine.  The keyboard works completely, but the RAM test failed on one block.  Repeated tests had different results usually hanging the machine.   I was able to load a couple demos and they seemed to work, aside from being in black and white.

 

Any thoughts on what might be causing the issues?  I'm assuming bad RAM, and maybe a bad GTIA?  Would it be worth trying to fix?

 

One other oddity I hadn't notice - the font on the keyboard is slightly different from what I'm use to on the 800XL.  Also the keys are light, silky smooth and are very easy to press.  I'm use to them being a bit more firm.  Were there different keyboards used or possibly an aftermarket keyboard?

[reifsnyderb]

Hello,

 

How did you have the 800XL connected when it came up black and white?  Did you have it connected via the 5 pin DIN monitor port or via the RF connection?

[Sardonyx]

1 hour ago, reifsnyderb said:

Hello,

 

How did you have the 800XL connected when it came up black and white?  Did you have it connected via the 5 pin DIN monitor port or via the RF connection?

Hello,  It was through the 5 pin DN monitor port

[+bf2k+]

Stock 800 XLs are missing the chroma signal on the monitor port.  Hence black & white only...

[Sardonyx]

1 minute ago, bf2k+ said:

Stock 800 XLs are missing the chroma signal on the monitor port.

Interesting.  I'm using a 4-connector cable that came with another 800XL I purchased.  That one has a UAV mod in it.  The cable provides composite, chroma, luma, and audio as RCA connectors out of the 5-pin DIN.  I was using the composite and audio as I don't have an adapter handy to take the separate chroma and luma into an S-Video connector.  

 

Would the pin out have changed to move the composite signal to another pin?  I can try the other 2 signals and see if composite might be on a different pin on the stock system.  

Or do you mean it just doesn't provide chroma at all, even on composite on a stock 800XL?

[reifsnyderb]

1 minute ago, Sardonyx said:

Hello,  It was through the 5 pin DN monitor port

It's normal for an 800XL to be black and white when using the 5 pin DIN monitor port.  Pin 5, chroma, wasn't connected.  On some machines, the display is a little "fuzzy", too.

 

The solution is to solder a 100 ohm resistor to pin 5 on the monitor jack then connect the other side of that same resistor via a jumper wire to the junction of R66, R67, R68, and Q5.

 

If the display is still fuzzy, and your computer has a capacitor C54, remove capacitor C54.

 

If you don't mind losing RF, you can further clean up the display by removing C54.

 

 

 

[+bf2k+]

No chroma at all on a stock 800XL.  I have done Brian's original mod to fix this years ago on one of my current machines and more recently installed UAVs on the rest of my 800XLs and my 600XL.

 

The composite signal has color.

 

I never noticed the problem on my original Amdek Color 1 monitors... they were composite.  But when I got a Commodore 1702 which has chroma and luma inputs, it bit me.

[Draxxs]

Chroma is not on a stock ntsc machine at all.  You have to do the mod to get it to the 5 pin.

[Sardonyx]

I tried the different connectors on the 5-pin DIN cable.  I'm getting audio so that one is correct.  The composite connector, which does give color on the UAV modded 800XL is black and white on this 800XL.  I also just separately tried the luma and chroma connectors into the composite input in case the pins may have been swapped on the modded 800XL. The luma was black and white (as expected) and the chroma provided no signal (also as expected, even it was connected).

 

Just for clarity sake - would the composite output on a stock 800XL normally be black and white without the chroma mod? Normally composite on most devices would carry the luma+chroma signal by default.  Or is the chroma mod only needed to get color with separate chroma/luma?

 

[reifsnyderb]

8 minutes ago, Sardonyx said:

I tried the different connectors on the 5-pin DIN cable.  I'm getting audio so that one is correct.  The composite connector, which does give color on the UAV modded 800XL is black and white on this 800XL.  I also just separately tried the luma and chroma connectors into the composite input in case the pins may have been swapped on the modded 800XL. The luma was black and white (as expected) and the chroma provided no signal (also as expected, even it was connected).

 

Just for clarity sake - would the composite output on a stock 800XL normally be black and white without the chroma mod? Normally composite on most devices would carry the luma+chroma signal by default.  Or is the chroma mod only needed to get color with separate chroma/luma?

 

 

Composite has chroma connected but it's usually awful.

 

The pins are:

 

1 -- Luma

2 -- Ground

3 -- Audio

4 -- Composite

5 -- No connection in most "stock" 800XL's.  If modified, or one of the rare stock 800XL's this is the chroma pin.

 

 

 

From the back the pins are like this:

 

    3                      1

      5                  4

               2

 

 

 

 

Edited August 5, 2022 by reifsnyderb

[Sardonyx]

Just now, reifsnyderb said:

 

Composite has chroma connected but it's usually awful.

 

The pins are:

 

1 -- Luma

2 -- Ground

3 -- Audio

4 -- Composite

5 -- No connection in most "stock" 800XL's.  If modified, or one of the rare stock 800XL's this is the chroma pin.

 

 

I think something may be wrong then, the composite output seems to be black and white.   The video is very crisp, but no color.

I'm not sure if I have the connectors to hook up RF, but I can take a look and see if I still have an adapter to test it.  I may have to setup an old TV too, I don't think the one I'm using has an NTSC tuner in it.

[Sardonyx]

I was able to hook up RF and test it.  Wow!  I don't remember RF being that bad, but it's been forever lol

 

It did have color over RF, so that's something, but still only black and white over composite.  What could cause that?  I would think it would be the same composite signal running to the DIN connector and input into the RF modulator.

[reifsnyderb]

20 minutes ago, Sardonyx said:

I was able to hook up RF and test it.  Wow!  I don't remember RF being that bad, but it's been forever lol

 

It did have color over RF, so that's something, but still only black and white over composite.  What could cause that?  I would think it would be the same composite signal running to the DIN connector and input into the RF modulator.

That's a good sign.  The color circuitry works.  The composite is picked off of the same components the RF is taken from.  There may be some problem with your cable.  The only component that hasn't been checked is L7...and I sort of doubt that's bad as it's just a ferrite bead.  (I suppose anything is possible.)

 

If you can solder, doing the chroma fix I posted earlier is the cheapest way to get really nice S-Video output.  (With color, of course.)

 

Edited August 5, 2022 by reifsnyderb

[Draxxs]

Yep , I agree your cable is wrong or your on the wrong pin.  If rf is color then composite output will be color.  Break out a meter and check continuity of the composite from the back side of the connector out to the tip of the composite.  A nice black and white picture is gonna be your luma channel.

[Sardonyx]

38 minutes ago, Draxxs said:

Yep , I agree your cable is wrong or your on the wrong pin.  If rf is color then composite output will be color.  Break out a meter and check continuity of the composite from the back side of the connector out to the tip of the composite.  A nice black and white picture is gonna be your luma channel.

I suppose it could be cable, but both the luma and composite plugs come out as black and white on the 800XL I'm testing.  On my UAV modded 800XL, I'm using the composite plug and getting color from that.  Though to be fair I haven't checked the Luma connector on the UAV moded 800XL as my setup can only accept separate chroma/luma through S-Video and I need to get an adapter for that. 

 

I don't know for sure the cable works on a stock 800XL.  It's behaving like both the Composite and Luma RCA plugs are connected to Luma on this 800XL I'm trying to test.  I guess I could test it on the modded 800XL and see if the connector marked as Luma is outputting color as well or if it truly is a B&W Luma signal as it should be.  It's possible the cable isn't wired correctly or labeled correctly.  When it came with the modded 800XL I just plugged in composite and audio and it worked as expected so I didn't think more about it.

Edited August 5, 2022 by Sardonyx

[reifsnyderb]

I think some cables create composite in the cable by combining Luma and Chroma in the cable itself.  If this is what your cable is doing then you'll only get black and white on and unmodded 800XL.

Edited August 5, 2022 by reifsnyderb

[Sardonyx]

11 minutes ago, reifsnyderb said:

I think some cables create composite in the cable by combining Luma and Chroma in the cable itself.  If this is what your cable is doing then you'll only get black and white on and unmodded 800XL.

That makes sense, maybe that's what's happening.  I tested Composite and Luma connections on the cable from the modded 800XL into Composite input of my video setup.  Composite has color, Luma doesn't as you'd expect.  

 

If a stock 800XL feeds the same composite signal to the DIN connector and the RF modulator, I don't see how the color information could be present in the RF output, but not on the composite pin in the DIN cable.  So the cable being wired as you suggest would explain it.  I guess I'll order a regular Atari composite video cable and give that a try.

[sup8pdct]

There is a pot on the main board that controls colour that Gtia produces. Give it a little fiddle while on and see what that does. maybe a bit of oxide has formed and it isn't doing its job properly.

 

Chroma is a separate signal from Gtia that goes through its own amplifier circuit. Maybe something has gone bad there.

[reifsnyderb]

3 hours ago, sup8pdct said:

There is a pot on the main board that controls colour that Gtia produces. Give it a little fiddle while on and see what that does. maybe a bit of oxide has formed and it isn't doing its job properly.

 

Chroma is a separate signal from Gtia that goes through its own amplifier circuit. Maybe something has gone bad there.

@Sardonyx already proved the color circuit is working by trying RF.

[Draxxs]

Quote

 

Be careful of cables.  My first cable I bought on Amazon was listed as an Atari Video cable and one of the wires was not even connected inside. Been a while but it seems it was the composite that was not connected on the cable. It had the RCA jack for the pin but there was no connection.  I installed a UAV on the machine and went to S video and purchased a decent cable from a small company out of Canada.

[Mrshoujo]

Actially, the 800XL outputs full color composite video even while using the Monitor port. I have one of those 4 connector cables and figured out how to get composite video and audio on only 2 plugs. Don't use the separated chroma / luma. You can connect them if you really want to by doing the mods everyone knows. I never saw the need.

[Sardonyx]

18 minutes ago, Draxxs said:

Be careful of cables.  My first cable I bought on Amazon was listed as an Atari Video cable and one of the wires was not even connected inside. Been a while but it seems it was the composite that was not connected on the cable. It had the RCA jack for the pin but there was no connection.  I installed a UAV on the machine and went to S video and purchased a decent cable from a small company out of Canada.

So I used a multi-meter on the cable a little earlier this morning as a sanity check.  It looks like all the pins are connected to the plugs they're labeled as, and ground goes to all 4 outer rings.  

 

That leads me to think the cable is fine. It also works fine on the UAV modded 800XL it came with.  

 

But that means the theory from last night of the cable being made such that chroma+luma were tied together is not correct.  I get continuity from the composite pin to the composite RCA plug.  I also checked each of the 4 signals on the DIN connector and all they go to one unique plug.  There's nothing odd like Luma showing up on both Luma and Composite.  So it should be feeding whatever's on the composite pin in the 800XL to the composite video RCA plug.

 

Looking at a schematic for the 800XL it looks like the color for the Composite and RF outs are pulled straight from the same amps.  It's hard to see how one would have color and the other wouldn't.  The only component that looks like it's different is a ferrite bead (L7) that filters the composite line on the way to the DIN connector.

 

[Paul Westphal]

The only time I have seen black and white out of the monitor port, it was a chip problem or a shitty cable. Try replacing the small 8 pin chip (pic). A bad GTIA could also be the culprit.

[TGB1718]

7 minutes ago, Paul Westphal said:

The only time I have seen black and white out of the monitor port, it was a chip problem or a shitty cable. Try replacing the small 8 pin chip (pic). A bad GTIA could also be the culprit.

You have to love the propensity of modern camera's to focus on the background ?

[+kheller2]

Tap the comp line feeding the RF modulator OR can you test your monitor/cable with another non UAV XL?   Obviously there was a reason this XL was listed as for parts.