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A Question About Crystals.


DavidMil

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I have a 1220XL that the color keeps going in and out and lately the PC is always locking up. I have traced it back to the clock circuitry.

First I thought it was one of the transistors but changing them out didn't resolve the problem. When I put my scope on the crystal, it was

not stable and moved all over the place. Sometimes up to 4MHz but mostly down around 2.xxxMHz. So my question arises from the fact

that I don't have C061090 crystal, but I do have a C016010 crystal. Can I use the C016010 (from a 2600) in the 1200XL? They both

seem to have the same frequency.

 

Thanks,

DavidMil

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Probably... I needed a 14 MHz one for my 800XL with VBXE. In it's case you retain the colour gen crystal for the PAL machine and use the 14.1 which the VBXE divides down to provide the master system clock.

I got mine from a 7800. Then replaced the one from the 7800 with a generic NTSC 14 MHz crystal which I got from some old PC expansion card.

 

Weird that the clock would be all over the place. Maybe the quartz has a fracture or something? Generally the tolerance of these things is pretty tight.

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David I'm just wondering if you are trying to attach the scope directly to the crystal? Doing so would cause great instability in the frequency, which is what you say you are seeing. It would be preferred to scope it on the output side of the associated transistor oscillator circuit. An easy place to do that would be to scope pin-28 of the GTIA chip.

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David I'm just wondering if you are trying to attach the scope directly to the crystal? Doing so would cause great instability in the frequency, which is what you say you are seeing. It would be preferred to scope it on the output side of the associated transistor oscillator circuit. An easy place to do that would be to scope pin-28 of the GTIA chip.

 

Pin 28 of the GTIA chip was where I first discovered the problem. The 1200XL field service manual is so poor I use the 800XL manual for

trouble shooting. It says that no color or bad color (which I started having first) could be the clock circuitry. It was like the oscillator circuit

was 'skipping a beat' every now and then. The scope would have these random very short 'flat lines' (where the voltage didn't move). And

then it would start up again.

And yes I was putting the test lead directly to the crystal. Thank you for the new knowledge!

Ok, I'm open to suggestions here...

 

David

 

Other things: This was my first 1200XL and the boys played it for hours every day. I know for sure that it was dropped at least once. But

there is now telling what kinds of torture a couple of boys could do to a computer over the course of several years. I've done the 'simple'

trouble shooting (swapping all the chips including the delay chip) with known working chips in my other 1200XL. The problem stayed with

the bad 1200XL. VRegs are solid and stable. Game cartridges work fine except there is no color (or just a flicker of color every once in

awhile), at least until the machine locks up.

 

DM

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You know the story, especially if dropped and tortured by kids, time for the complete clean and re seat, look for failed sockets, cracked joints et al. While it is rare for a crystal to go bad, it can happen, rough treatment or not, I've had to resort to hot and cold machines for testing already for a couple of machine that no one could figure out, literally acted one way in the cold another in the warmest room. Turned out to be a complex issue, some components were failing at the edges of the operating temperature ranges, yet sort of worked at normal temperature so it was a moving gremlin. replaced a socket, a transistor, and a support IC that were all supposedly good, but were marginal in reality. Problem solved on that one. Same deal sort of but not quite with a crystal, depending on the temperature it worked perfect or would become erratic (I suspected it was cracked inside and would either contact fully at one temp and not so much at others.

 

Sometimes swapping stuff just because, after all else had failed works... I just had to know why so I dedicated way to much time on such science experiments...

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Well so much for my Crystal solution...

I don't remember what I was doing but I pressed down on the board just a bit to the right of R13 and the screen went

black and the computer locked up. So I guess I'm going to reflow every thing around R13 and then I'll break out the

wife's high powered magnifier to look at components. Also I'll have to connect the leads to end points of all traces

around there and press on the board again to see if I get any open traces. It's a good thing I enjoy (well mostly enjoy)

figuring out these kinds of problems.

 

David

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The saga continues...

After reflowing all the components within an inch of R13, I decided to do the GTIA chip too. When I pulled out the chip, part of the single

wipe pin from position 21 fell out of the socket too. I thought I had discovered my problem but when I desoldered the socket several

other pins fell out of the plastic before I could even turn the board back over! Not good, not good. So I decided to look at the ANTIC

socket too. Yes, several of the pins were very loose there too. Only two pins fell out while desoldering that socket. One fell out of the

CPU socket too. So now I've decided to replace every socket on this 1200XL. I don't have enough 40 pin sockets to replace all of them

now, so tomorrow I'll call Brad and order some more. I have a special feeling for this old computer, or I swear I'd pull all the chips out and

drop the system board in the garbage at this point!

 

DavidMil

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napoleon-dynamite-time-machine.jpg

 

Always use the proper crystal! Especially for 1982 era equipment. Then your Atari will launch that football over them mountains.

 

After I changed out all the sockets and the machine quit being 'flaky', I tried swapping out the crystals. You would think that .0009 MHz wouldn't create any problems,

but it was enough that the 1200XL came up and worked without any problems...

Except there was no color, only a black and white image. Like you said Stephan," Always use the proper crystal."

 

DavidMil

Edited by DavidMil
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Beautiful work there! Love seeing all those big 40 pin machine sockets in place. That would take me ages with my lowly thumb-press suction pump. Maybe one christmas I'll get one of those fancy desoldering stations :)

 

I recently stocked up on these machine sockets...

https://www.aliexpress.com/item/10PCS-Round-Hole-IC-socket-Connector-DIP-6-8-14-16-18-20-24-28-pin/32888818828.html

 

Grand total of $11.11 (free shipping) for 40 sockets: 20x28 pin, and 20x24 pin sockets. Took about a month for delivery.

 

Then from eBay:

https://www.ebay.com/itm/182144230222
10PCS DIP40 40Pin SIP Round IC Sockets Adaptor Solder Type gold plated machined
10 for USD $3.51, Free shipping

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Beautiful work there! Love seeing all those big 40 pin machine sockets in place. That would take me ages with my lowly thumb-press suction pump. Maybe one christmas I'll get one of those fancy desoldering stations :)

 

 

Thank you Nezgar. If you can swing the $120 or so dollars, it's really worth it. I removed all those bad sockets in a little over an hour.

 

David

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After I changed out all the sockets and the machine quit being 'flaky', I tried swapping out the crystals. You would think that .0009 MHz wouldn't create any problems,

but it was enough that the 1200XL came up and worked without any problems...

Except there was no color, only a black and white image. Like you said Stephan," Always use the proper crystal."

 

DavidMil

 

David,

The chroma line was not connected to the monitor port on the 1200XL. How are you connecting the computer to the monitor?

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I've modified all of my 1200XL's with a video upgrade from a guy named Bob Woolly. I use his ClearPic 2002 upgrade.

The improvement is really amazing! Especially when using S Video. I don't know if he ever did another improvement

to this upgrade... Anyone Know (hint, hint Bob)?

 

DavidMil

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I missed this thread until now - dude, next time make it clear it's a 1200XL in the subject line! :)

 

Yeah, the stock Atari single-wipe sockets suck donkey balls. I had to replace three of the 40-pin sockets in my Ugly Duckling 1200XL during my restoration of that machine. Note pin 19 on this one: broken right off at the bend. Bah.

 

post-30400-0-64414700-1550370323_thumb.jpg

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I missed this thread until now - dude, next time make it clear it's a 1200XL in the subject line! :)

 

Yeah, the stock Atari single-wipe sockets suck donkey balls. I had to replace three of the 40-pin sockets in my Ugly Duckling 1200XL during my restoration of that machine. Note pin 19 on this one: broken right off at the bend. Bah.

 

attachicon.gifPin19.jpg

 

Sorry DrVenkman. Here's a picture of all the bad/loose pins:

Don't know why but the pins in the PIA chip were fine. I don't think I every replaced it before...

 

DavidMil

post-47264-0-76396500-1550379130_thumb.jpg

Edited by DavidMil
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I modify my 'working' 1200XLs by removing R63, C115, and L15, and replacing them with wire (1 ohm resistors, actually). Add a wire from the left side of R186 (looking at the component side of the PCB) to the empty pin of J5 (the video DIN). This is a CHROMA pickoff.

 

You can also either remove C60 or replace it with a smaller value, like 39pf. This affects your noise/bandwidth - sharp characters or noise in the background.

 

Bob

 

 

 

 

I've modified all of my 1200XL's with a video upgrade from a guy named Bob Woolly. I use his ClearPic 2002 upgrade.

The improvement is really amazing! Especially when using S Video. I don't know if he ever did another improvement

to this upgrade... Anyone Know (hint, hint Bob)?

 

DavidMil

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I modify my 'working' 1200XLs by removing R63, C115, and L15, and replacing them with wire (1 ohm resistors, actually). Add a wire from the left side of R186 (looking at the component side of the PCB) to the empty pin of J5 (the video DIN). This is a CHROMA pickoff.

 

You can also either remove C60 or replace it with a smaller value, like 39pf. This affects your noise/bandwidth - sharp characters or noise in the background.

 

Bob

 

So you don't remove Q8 and all the other components from the 2002 upgrade anymore?

 

David

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