Fixing an Atari Najm 65XE

[atari65xenajm]

Hello,

 

I finally was able to put my hands on my 1989 Atari Najm 65XE 8-bit computer. I knew from before it did not display anything on screen and the potentiometer R38 is broken.

 

When I opened it up and removed the RF shield, I noticed when the computer is powered up, the 6502C chip heats up very fast.

 

Does this mean this CPU is faulty?

 

Also, does anyone know where I could purchase another R38 (and a CPU if you believe it is faulty)?

 

I appreciate any help in trying to get this computer back to operational!

[atari65xenajm]

I reached out to Brad from Atari Best Electronics. I purchased a pot, the CPU, GTIA, and ANTIC chips (these three ICs were super hot). There was one resistance L25 that was burned off, which I replaced with a 10 ohm + 5% tolerance per the online schematics of the Atari 130XE.

 

Still no luck. I sometimes get a blank screen with no READY prompt. The ICs still get hot.

 

Any advice on what I should do next?

[Guest]

CPU GTIA and ANTIC still getting hot?

 

or other board ICs?

 

which version of the XEN is it? 65xe (8x ram)

or 130xe (2 of 4 ram chips)

Edited January 24, 2018 by Guest

[_The Doctor__]

check the power supply, if you've replaced all those chips and they are all getting too warm or hot again you've got power rail problem or power / ground loop from or through display

now you know to check the support chips, transistors, diode and caps, hopefully non have shorted, also make sure the insulator is between the lower shield and pcb, I've seen them bent and legs touch...

Edited January 24, 2018 by _The Doctor__

[atari65xenajm]

CPU GTIA and ANTIC still getting hot?

 

or other board ICs?

 

which version of the XEN is it? 65xe (8x ram)

or 130xe (2 of 4 ram chips)

Yes. The CPU/GTIA/ANTIC ICs are the ones getting hot. The version of XEN is 65XE Rev 2. Please check the picture in case my guess of the version is incorrect. Thank you.

 

Edited January 24, 2018 by atari65xenajm

[atari65xenajm]

check the power supply, if you've replaced all those chips and they are all getting too warm or hot again you've got power rail problem or power / ground loop from or through display

now you know to check the support chips, transistors, diode and caps, hopefully non have shorted, also make sure the insulator is between the lower shield and pcb, I've seen them bent and legs touch...

 

Thank you. I used to have an Ingot power supply back in the early 1990s which I believe may have caused damage (I read about it online very recently and this is when I decided to try to fix it). I have purchased a brand new Atari 130XE with the C061982 power supply and I know it simply works. I have checked the lower shield and the PCB (and in fact removed the lower shield and placed the PCB on a cardboard box. Still same thing.

 

I think checking the support checks, transistors, diodes, resistors, and caps may be a time consuming exercise for me, but I am willing to do it if nothing else is likely to be faulty.

[_The Doctor__]

unless it's a trick of light, I see solder joints not filled in on components down in the lower left and upper left, make sure components are not rubbing IC pins. Give the board a good look over for cracked joints and low flowed joints.

[Geister]

I'd also take a close look at the capacitor and resistor down near the 555 timer chip. It looks like something is corroded or bridged there.

[atari65xenajm]

Thanks everyone. I have attached two more pictures here. I hope this sheds more clarity on whether the 555 IC or its surroundings are problematic (this bridge was like this even when the computer was working back in the 80's-90's).

 

As for the soldering of the CPU and ANTIC, I will de-solder and re-solder these two ICs and re-straighten the IC legs sometime during the weeknd and let you all know the outcome. Thank you again.

 

[_The Doctor__]

Wow that's a mess, I would have put sockets in when replacing the chips, I see blobs on some legs, underflow on others, some bad or cracked joints, I see some flux or other contaminants and blobs on the legs of c014806 the cap just below it needs reflow. What I see concerns me I am worried some pins were extremely over heated why others weren't heated enough...

 

I also see solder flecks lying about, I would make sure to brush off the board, flux both sides of the board and clean it up removing the blobs and adding quality 40-60 solder to anything suspect. after that it might be okay if not, you going to have to test chips again, I am crossing my fingers that they're OK

Edited January 25, 2018 by _The Doctor__

[flashjazzcat]

Yep: The CPU alone is lacking solder on the IRQ pin (pin 4), O2 (pin 39) and A8-A11 over on the right hand side, plus several others. Not much hope of working until that's all taken care of.

[+kheller2]

Do we have a dump of this version of the OS? The date on the OS ROM sticker -- is that the burn date or OS version date, because I don't see that in Kr0tki's list. Although it might just be the bb1r59a.rom from here: http://atariage.com/forums/topic/217772-atari-400800-os-b-pal-the-real-mccoy/?p=3238760

[charliecron]

This thread got me to pull mine out. I could not remember if mine was PAL or NTSC but I dug up an old thread, and it's PAL. I've got a cheap USB capture thingy now that can do PAL, still, it would not work. I felt my chips, found a hot RAM chip, swapped it out, and it boots! I also didn't realize that Prowizard mentioned I was missing a color pot on my board. So I pulled one off an 800XL board because why not, and I'll be dammed I got a blue screen! I do remember it being only black and white the one time I had it working, but I thought that was cause I didnt have a PAL monitor. Well, I have the same board pictured here. I think I used a wrong chip though, cause it's only showing 48k. I think the chip I used was extra from a RAMBO upgrade I did on another machine. I'll try to pull a chip off an 800xl and see if I get 64k another night.. here is a terrible picture. You can see my terrible job on the RAM chip, it's the second one from the top.

 

[+Stephen]

The RAM test will only show 48kB (or 40 if BASIC is enabled).

[atari65xenajm]

Wow that's a mess, I would have put sockets in when replacing the chips, I see blobs on some legs, underflow on others, some bad or cracked joints, I see some flux or other contaminants and blobs on the legs of c014806 the cap just below it needs reflow. What I see concerns me I am worried some pins were extremely over heated why others weren't heated enough...

 

I also see solder flecks lying about, I would make sure to brush off the board, flux both sides of the board and clean it up removing the blobs and adding quality 40-60 solder to anything suspect. after that it might be okay if not, you going to have to test chips again, I am crossing my fingers that they're OK

 

Thanks for your input. I must admit this is the first time I get myself into soldering, so I will do my best not to mess up the next attempt. I had asked Best Electronics for sockets, but he did not seem to have the right ones. Any idea where I could buy them?

[+DrVenkman]

Sockets are easy to find on eBay or from retailers like Digi-Key, Mouser, Jameco or others. Some prefer machine pin precision sockets, others are fine with double-wipe sockets. Precision sockets are a bit more expensive.

[+kheller2]

What was the point of Atari doing the XEN board? The 130XE board with an empty 8 RAM sockets is not the same thing?

its also odd the XEN is using 8 sockets instead of the latter 2 version.

[_The Doctor__]

Because different teams get assigned to projects and they don't bother looking at the entire line to get a result? Perhaps the person overseeing the projects was too busy with someone or something chemical to notice, alcohol could be involved... er um Let's re-use this other board and put a different silk screen on it, nobody will notice and we'll get paid! I know I'm being a bit wild in what I'm saying but look at the entire line XL and XE shuffle them around and you might only find subtle differences or maybe none at all...

Some one counting beans thought they could save money based on the board and didn't consider the cost of fabrication of new boards? Hey just keep it rolling!

Edited January 26, 2018 by _The Doctor__

[atari65xenajm]

Thanks to all for your inputs. I found the 42 pin socket on eBay and will purchase a couple. But before I do, I wanted to ask you if this motherboard is still usable (after my de-soldering attempt), or is it declared dead?

 

Also, one of the legs of the CPU IC got bent too hard when I tried to fix it, it broke from its mounting point (it is the RES pin). Can anything be done at this stage with it (assuming the board is not declared dead)?

 

Thanks again.

 

 

 

[_The Doctor__]

it's repairable, you've got a couple cut traces, and a few pulled pads, and at least one that's gone. it's can easily be trace repaired or hard wired... I suggest you have someone do the work for you. I would buy scrap x86 boards and parts to practice my skills on before working on delicate retro computers. The scrap boards can be had for less than scrap prices pretty often on ebay or even for free (CURB ALERT).

 

I use high temperature epoxy glues and copper sheet/foil for such repair, even thin gauge copper wire strands, The copper must be connected to original traces and thru holes then epoxy/glued down using the epoxy/glue under the new trace and then some people brush it over the area that would normally have solder mask or even buy a tube of colored solder mask to finish the job.

 

This is work for a skilled individual at this point, please consider one of the many people here on AA to do this for you, the XEN board deserves to be restored.

 

If a chip leg is broken that too can be repaired depending on the break and length of what is left on the chips...

Edited January 26, 2018 by _The Doctor__

[atari65xenajm]

Thank you . I certainly do not mind sending my board (along with all the ICs I have) to anyone who could fix it.

 

If anyone is interested in fixing this mess I caused, please send me a PM with your cost and time estimates. Thanks again!

[+Stephen]

Thank you . I certainly do not mind sending my board (along with all the ICs I have) to anyone who could fix it.

 

If anyone is interested in fixing this mess I caused, please send me a PM with your cost and time estimates. Thanks again!

PM sent

[atari65xenajm]

I had purchased a faulty Atari 65 XE Najm computer from some stranger in Egypt (calling it computer #2 to avoid confusion). It also turned out to be a 65 XEN motherboard though the Arabic OS was an older version (i.e., numerals will always be Hindi and no lower case English can be typed using the Shift+Help shortcut).

 

This motherboard had a very hot CPU as well, but this time, and after the mess I apparently created with motherboard 1, I decided to give myself a second shot, and I hope I succeeded! The READY prompt can be seen, and I hope I did a better de-/soldering job here. You may notice this motherboard has nothing socketed. I wonder if Atari had single quality control process or several quality control check processes for the production of this model. The motherboard I messed up has a socketed Arabic OS ver 2 which is something our friend @Madi covered in a posting of his.

 

Leaving you with some pictures of computer #2 (sorry if they are rotated 90 degrees---I took the pictures with a correct angle from phone).

[_The Doctor__]

NICE, good job!

This makes the night a little better!

A little cheer can go a long way.

[atari65xenajm]

Thanks to all for your inputs. I found the 42 pin socket on eBay and will purchase a couple. But before I do, I wanted to ask you if this motherboard is still usable (after my de-soldering attempt), or is it declared dead?

 

Also, one of the legs of the CPU IC got bent too hard when I tried to fix it, it broke from its mounting point (it is the RES pin). Can anything be done at this stage with it (assuming the board is not declared dead)?

 

Thanks again.

 

 

Hi all,

 

Our AA friend @Stephen has kindly offered to repair the board. I hope that we all hear something positive from him now that the board is in better hands!