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Another 130XE Memory Failure


hatchcliff

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There is a lot of good advice on the forum about fixing 130XE's with broken memories. When mine failed I found all the information I needed here and here, but there are many other good posts too. Thanks to everyone who has posted on this topic. I'm not very experienced with hardware, and there is no way I could have repaired my machine without your guidance.

 

Just for the record, here's a description of the fault and repair in pictures:

 

The machine starting booting to the ROM/RAM test.

130xe Ram failure

 

Case opened, showing the 16 RAM chips on the left hand side.

Case Opened

 

Original chips. One is an NEC 4164, but the other fifteen are the notorious MT 4264's.

130xe original Ram

 

Chips removed by snipping the pins, withdrawing them one at a time with a soldering iron and tweezers, and finally clearing the holes with a solder sucker.

130xe Ram removed

 

Sockets soldered in place and new chips installed. I chose 41256's to give me the easy option to upgrade the machine to 320K in future.

130xe New Ram

 

Fixed!

Fixed

 

I still have one question on my mind. Opinions vary on whether it is necessary to tie the unused address line (A8, pin 1) on the 41256's to ground (or possibly I have misinterpreted the opinions). I have not done this yet, but the machine has run perfectly well for days on end. This seems to imply that the chips respond in a predictable manner to disconnected address lines. Can anyone confirm if this is the case?

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I guess there is some stability of that line though but Self Test Ram test isn't the be-all-end-all decision maker.

 

Instability issues reported here in the past have had strange ways of showing, you might get different behaviour for repeated (same address) accesses, after Rom read, after Refresh cycle, after Antic access, whether a cartridge is present, etc etc.

 

For a >=256 upgrade you'd need those lines tied together anyway in at least one of the rows. I guess ultimately you could just leave as is but there might come a time where it starts acting up and you won't know whether it's the Ram or not.

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It is indeed a Nikkai, and I did get mine from Maplin in the UK.

 

It's a 10.2" television. You have to set the aspect ratio to a narrow 4:3 to get the right image with an Atari, so I would guess it's equivalent to a 5 or 6" monitor. A bit small, but it can be set close to the keyboard and I find it very useable - also handy for storage.

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I still have one question on my mind. Opinions vary on whether it is necessary to tie the unused address line (A8, pin 1) on the 41256's to ground (or possibly I have misinterpreted the opinions). I have not done this yet, but the machine has run perfectly well for days on end. This seems to imply that the chips respond in a predictable manner to disconnected address lines. Can anyone confirm if this is the case?

 

Better safe than sorry. Tie it to ground. It's hard to say how a chip will respond to a floating input, but I wouldn't want to take a chance that it'd try to write to the lower half of the chip then read from the upper half.

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I've been trying to fix a 130XE myself. Unfortunately without much luck.

 

The Freddie, OS and Basic were dead.

The Processor, Antic, GTIA, PIA, Pokey are all ok.

Same with the CO61618 and the CO25953

 

I read that trying to put the Asteroids cartridge on the system would help to diagnose.

But still, nothing.

 

Could it be one of the IC's?

CD4050BE, 74LS74, 74LS138, 74LS08 and 2x SCL405IBE

 

The major problem is that the PCB is one of those chinese boards.

It's even likely that eventhough I was very carefull with soldering, that one of the traces broke.

 

Any help or suggestions would help! :-)

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Instability issues reported here in the past have had strange ways of showing, you might get different behaviour for repeated (same address) accesses, after Rom read, after Refresh cycle, after Antic access, whether a cartridge is present, etc etc.

 

I guess ultimately you could just leave as is but there might come a time where it starts acting up and you won't know whether it's the Ram or not.

Better safe than sorry. Tie it to ground. It's hard to say how a chip will respond to a floating input, but I wouldn't want to take a chance that it'd try to write to the lower half of the chip then read from the upper half.

 

Thanks for this. I will go ahead and complete the repair. I agree that it is far better to tie the disused pins to ground than to risk unpredictable read/write errors in the future.

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I also apologize for hijacking this topic, but regarding the small tv screen -- I have a tip. Portable DVD players are dirt cheap these days. If you look around, you can find one with AV input jacks. I have one, and use it for vintage gaming machines. In fact, the DVD portion makes a nice little stand for the machine being used. Just another option for those looking for a small screen.

 

For example:

 

http://www.bhphotovideo.com/c/product/752567-REG/Sony_DVPFX970_DVP_FX970_9_Portable_DVD.html

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A/V only kinda blows though - the big tragedy is that S-Video is the poor piggie in the middle and is being pushed out. A/V is the lowest common denominator and present on most TVs.

 

The other big tragedy is that Component is also getting the boot - my new BluRay player only has HDMI and A/V - the reasoning being that component is almost HDMI quality but able to be used for copying stuff... although someone forgot to tell these people that BluRay encryption was cracked years ago.

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