Super Video 2.0 mod gone bad

[dkerfoot]

So I decided to do the 8-bit Alchemist's Super Video 2.0 mod on my 800xl. Things seemed to be going well until I plugged it back in and I now have a very crisp clean monochrome output. Color is gone whether I use the monitor port or the RF jack.

 

I have checked and double-checked and I see nothing visibly wrong. I was an electronics tech in a past life, but it has been many years and I don't know much about the workings of this video circuit. Does anyone know the circuit well enough to narrow down the possibilities (based on sharp mono picture but no color)?

 

I do have an o-scope available if needed.

 

Thanks for any help or suggestions.

 

-Doug

[Rybags]

PAL or NTSC machine?

 

Do you have a link to the page where you got the instructions? There's a few variations around.

 

I did one of the mods too and found a similar problem, I only get proper colour representation when using the Colour/Luma from the monitor port.

 

IMO the mod in itself is kinda flawed because the colour in itself isn't really at fault, the main problem is lack of definition with the luma portion.

 

So the solution would be to leave the colour alone for the most part, although I'm not sure you can do one without affecting the other.

[Bryan]

I'm not sure about the SV2.0 mod, but some mods remove the chroma-luma mixing at the composite jack to provide a cleaner s-video signal. If that is the case, then you won't have composite until you restore the resistor and capacitor between the two signals.

 

EDIT: Composite is made up of a chroma-luma mix via components R56, C54 and R67. The problem is, luminance will show evidence of the color carrier if these components are installed due to the crude mixing method used.

Edited August 21, 2011 by Bryan

[Faicuai]

Oddly enough, I had a very similar problem with my 800XL, albeit mine did not have super-video 2.0 or any of those parts-ripping variants.

 

My machine is RevC, HongKong, fully socketed. Only did power-reroute from C3 (which is definitely recommended), C56 out, and chroma-signal pin enabled (NO resistor added of any kind, whatsoever, just a good-caliber cable with decent/nice soldering).

 

One day, I turned it on and I had NO video signal AT ALL on s-video but (strangely) composite signal did work (the above mod. mantains all RF/Composite/Y+C signals fully operational, mated with the proper cable). It turned out the problem was at the cable itself.

In your case, If RF or Composite signal fails, the problem is pretty easy to trace on the MoBo, and you can actually JUMP each individual/intermediate point (relevants) from the luma or chroma signal path straight into the video-jack directly (they are separate and join at ONE point, on the Composite/Y-C output path), so you can quickly isolate the offending part.

 

I recently troubleshooted a 800XL that had a totally wrecked video-signal, especially in Composite and Y/C (both components). Culprits turned out to be:

 

a. A small capacitor in the chroma-path right before combination,

b. an 800 "JayMiner" Antic that some idiot dropped in place of the XL-series Antic, and

c. a specific 16-pin chip that handles luminance, pretty close to the antic, on the middle-left side of the MoBo.

 

After this, the machine worked out superb. SuperSalt Diagnostics was used to troubleshoot luminance. A simple Multimeter was used to check for every single resistance's correct value (per 800XL schematics and/or color-codes on the resistors), and test leads as jumpers for sending intermediate signals straight to the video jack. I followed the video-path (Y/C) carefully from the jack back into the MoBo traces, step-by-step.

 

I strongly suggest you to get a fresh, original copy of the 800XL service manual, which includes full schematics. It will help you today, and FOR EVER.

 

F.

[+wood_jl]

b. an 800 "JayMiner" Antic that some idiot dropped in place of the XL-series Antic, and

 

What's a "JayMiner"?

 

 

But you can confrim that the 400/800 ANTIC is different from the XL ANTIC? I bought PAL 130XE from B&C Computervisions, and also some replacement PAL ANTICs. When I was asking about buying the ANTICs (extra, of course) Bruce didn't know right away if he had any, and it sounded like he was going to pull them from a beige PAL 800. Now I'm wondering if I have ones that won't work????

 

Can people here confirm: Will a PAL ANTIC out of a beige PAL 800 work in a PAL 130XE?

 

Thanks.

[Faicuai]

But you can confrim that the 400/800 ANTIC is different from the XL ANTIC?

 

Correct (NTSC are different, and carry different part-numbers).

 

 

I have recently amassed a mini-kit/stock of ALL NTSC key internals, for both the "JayMiner" and "XL" series. When ordering ANTICs for both machine-classes (NTSC), I had to specifiy correct part numbers to Best Electronics.

 

 

NOTE: on 800XL schematics, Antic specifically/clearly appears as U7 / ANTIC "E"

 

 

F.

[dkerfoot]

Thanks for the replies. Here are answers to the questions:

 

NTSC

http://www.wolfpup.net/atarimods/supervid2.html

 

 

Some of the replies puzzle me a bit - did I make it clear that both RF and Composite work, but the picture is grayscale (no color at all) for both of them? Just for clarity - color worked fine on both RF and composite before the mod.

 

 

 

Here are the steps (condensed):

 

1. Replace R53 with 75 Ohm

2. Remove C56 (Mine was already vacant)

3. Replace R116 with 2.2 Ohm

4. Replace R66 with 75 Ohm

5. Add a 10uF capacitor R116 - R66 (original instructions reverse step 4 and 5 - after soldering the cap to R66, replace R66 - Doh!)

6. Add Composite Video disable switch inline with R56

7. Add 100 Ohm Chroma pickoff resister from R67-R68 junction to Pin 5 of the monitor jack

 

I don't currently have S-Video working. I suspect it may be an issue with the cable I bought but I don't know for sure. It is a dual composite/S-video cable - composite side tested fine (with color) before the mod.

 

 

The mod step 7 adds Chroma. R56, C54 and R67 were not messed with except to add the switch.

 

Composite works with switch closed, but with no color at all - just grayscale (very sharp grayscale!) Opening the switch kills composite of course.

RF works regardless of composite switch position - just grayscale - predictably fuzzier than the composite.

 

I have tried removing the Chroma Pickoff resister and the 10uF cap with no apparent change.

 

Does ALL the color signal come through Q4? If so, I am now thinking it would have to be a Q4/R66 problem to kill color to both the composite and the RF (or something upstream from there). A problem anywhere else looks like it might kill one, but not the other. Does that make sense?

 

I do have the service manual schematics on .pdf Does the service manual have any kind of O-Scope signal tracing information? That would be helpful.

Edited August 22, 2011 by dkerfoot

[sloopy]

the only difference between a '800 -C012296/ CO14887 (NTSC/PAL)' antic and a 'XE -CO21697/CO21698' antic is the DRAM refresh circuit...

 

the XE version has an extra bit of DRAM refresh needed for more then 64k, and in a 800XL, if memory is a stock 64k either will work equally well, and if the machine is upgraded to 192k (256k), or 448K (512K), then either need a newer ANTIC, or a extra circuit for the additional refresh...

 

when getting replacment parts, the C021697 will work in either machine, and would generally be preferred for 'in stock' replacement parts for people who repair A8's

 

 

sloopy.

[+bob1200xl]

Before you get crazy here, turn the color adjustment pot some - see if the color comes back. They get flakey...

 

Bob

 

 

 

Thanks for the replies. Here are answers to the questions:

 

NTSC

http://www.wolfpup.net/atarimods/supervid2.html

 

 

Some of the replies puzzle me a bit - did I make it clear that both RF and Composite work, but the picture is grayscale (no color at all) for both of them? Just for clarity - color worked fine on both RF and composite before the mod.

 

 

 

Here are the steps (condensed):

 

1. Replace R53 with 75 Ohm

2. Remove C56 (Mine was already vacant)

3. Replace R116 with 2.2 Ohm

4. Replace R66 with 75 Ohm

5. Add a 10uF capacitor R116 - R66 (original instructions reverse step 4 and 5 - after soldering the cap to R66, replace R66 - Doh!)

6. Add Composite Video disable switch inline with R56

7. Add 100 Ohm Chroma pickoff resister from R67-R68 junction to Pin 5 of the monitor jack

 

I don't currently have S-Video working. I suspect it may be an issue with the cable I bought but I don't know for sure. It is a dual composite/S-video cable - composite side tested fine (with color) before the mod.

 

 

The mod step 7 adds Chroma. R56, C54 and R67 were not messed with except to add the switch.

 

Composite works with switch closed, but with no color at all - just grayscale (very sharp grayscale!) Opening the switch kills composite of course.

RF works regardless of composite switch position - just grayscale - predictably fuzzier than the composite.

 

I have tried removing the Chroma Pickoff resister and the 10uF cap with no apparent change.

 

Does ALL the color signal come through Q4? If so, I am now thinking it would have to be a Q4/R66 problem to kill color to both the composite and the RF (or something upstream from there). A problem anywhere else looks like it might kill one, but not the other. Does that make sense?

 

I do have the service manual schematics on .pdf Does the service manual have any kind of O-Scope signal tracing information? That would be helpful.

[Faicuai]

I don't currently have S-Video working. I suspect it may be an issue with the cable I bought but I don't know for sure. It is a dual composite/S-video cable - composite side tested fine (with color) before the mod.

 

The mod step 7 adds Chroma. R56, C54 and R67 were not messed with except to add the switch.

 

Composite works with switch closed, but with no color at all - just grayscale (very sharp grayscale!) Opening the switch kills composite of course.

RF works regardless of composite switch position - just grayscale - predictably fuzzier than the composite.

 

I have tried removing the Chroma Pickoff resister and the 10uF cap with no apparent change.

 

 

Some specific observations:

 

 

1. Set Scope in Conitnuity-test mode, and check for EACH of Cable's pins (from A800XL-side to RCA and s-Video ends), pin by pin. You need pin-out to make sure that Composite, Y, C, Audio lines are active and PROPERLY connected.

2. If cable is Ok:

....a. Fully dissassemble machine (remove shields), and rest MoBo on bottom-plastic shelf.

....b. Connect the whole thing (A800XL, power supply, s-Video/Composite cable on S-VIDEO, and monitor), and fire them up (leave at Ready or Self-Test intro).

....c. Find one multimeter test-lead (sharp/fine ends).

....d. JUMP (manually, with test-lead ends) chroma output at juncture of R67/R68 (or "Chroma" from now on) STRAIGHT to Chroma-Pin at monitor-jack. Check for on-screen chroma-response.

....NOTE: You may need to reverse MoBo upside-down if video-jack conceals pins on the top-side.

 

....e. If d. above is negative (in the following order):

........i) Check R67 resistance (should be about 75 Ohm)

........ii) Check R68 resistance (should be about 3K Ohm)

........iv) Check Q4 output and then check Q5 output (can't give you some readings from my working 800XLs as they are all assembled. Will have a VERY LONG day at the office, tomorrow),

........v) Check for every surrounding resistor's value(R58, R59, R60, R61, R62, R63, R64, R65, R66, R97).

........vi) Check for Q2's output.

........vii) Check U20 (short north-bound legs with your finger-tip and check for screwed-up/flashing/distorted chroma response on-screen

........(=> Here, my secondary 800XL was losing chroma signal, COMPLETELY, even though U20 handles LUMA)

........NOTE: an acceptable way to discard or identify U20 is to run SuperSalt's gray-bar test and make sure entire gray-bar gradient shows up.

 

 

.....f. if d. above is positive (in the following order):

........i) Connect Cable's COMPOSITE end to Monitor/TV.

........ii) JUMP Chroma from INPUT trace/point of C54 to output trace/point of L7 (going to monitor jack's composite). Check for on-screen Luma & Chroma delivery.

........iii) JUMP Chroma from INPUT trace/point of C54 to input trace/point of L7 (going to monitor jack's composite). Check for on-screen Luma & Chroma delivery.

........iv) JUMP Chroma from OUTPUT trace/point of C54 to (input or output) trace/point of L7. Check for on-screen Luma & Chroma delivery.

........(=> Here, my secondary 800XL SUCKED big time.)

 

 

If you reach this point with a totally absent chroma response (on-screen), and assuming your TV/Monitor chroma processing is not fried, it is possible that you have a deformed or damaged chroma-signal that cannot be properly locked by the TV, though. In this case, I would have to open my secondary 800XL, and start with triggering composite signal's waveform in every step of the way (relevant), beginning on e) above, and show them to you, so you can compare on your end how yours look/read in the same test-point sequence. You will need a scope capable of natively triggering NTSC/PAL TV-signals, non-interlaced, with the ability to select a specific TV-line. This will certainly take some time, maybe this entire week.

 

F.

[José Pereira]

b. an 800 "JayMiner" Antic that some idiot dropped in place of the XL-series Antic, and

 

What's a "JayMiner"?

 

It's an A8, best not to have some people thinking it's another thing and in future this is AA, and ..., and the ... it's ...

 

In the eighties I think that I bought a computer called Eight Hundred Extra Large that was part of A8 family.

Exactly like the 800 "Jay Miner"

See it's not difficult... Just some more words but you have to learn to call things in their real and correct names

Edited August 22, 2011 by José Pereira

[dkerfoot]

Thanks for the suggestions. I had a solder bridge on R65. It took a while to find because my mullti-meter stopped working. Color is back and the video is very sharp!

[dkerfoot]

Thanks for the suggestions. I had a solder bridge on R65. It took a while to find because my mullti-meter stopped working. Color is back and the video is very sharp!

 

 

I'll also add that I got my S-Video working as well and had a great time playing Star Raiders on my 67" LCD TV! I am very impressed with just how good it looks and plays on the big screen.