Author Topic: Two for one on hardware issues  (Read 3067 times)

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Offline Bryce

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Re: Two for one on hardware issues
« Reply #25 on: 14:28, 09 July 18 »
IC114 and IC115

Bryce.

Offline walterg74

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Re: Two for one on hardware issues
« Reply #26 on: 22:06, 09 July 18 »
IC114 and IC115

Bryce.


Great... more buying and worst of all waiting for it to arrive  ???


Any particular variant, or any plain old 74LS244 & 74LS373..?


I would think the PAL would not be the culprit, being I did the remove and rewire trick, right..?

Offline Bryce

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Re: Two for one on hardware issues
« Reply #27 on: 22:17, 09 July 18 »
Unless of course the upper RAM is also damaged? But that would seem less likely as it would mean two things had failed simultaneously.

Bryce.

Offline walterg74

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Re: Two for one on hardware issues
« Reply #28 on: 22:20, 09 July 18 »
Unless of course the upper RAM is also damaged? But that would seem less likely as it would mean two things had failed simultaneously.

Bryce.


Well in any case I finished the second half today and installed all new RAM, same thing.

Offline Bryce

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Re: Two for one on hardware issues
« Reply #29 on: 22:40, 09 July 18 »
Try testing the output pins of the buffers mentioned above, but also the outputs of the multiplexers (74LS153's). All of these could could be the cause of the issue.

Bryce.

Offline walterg74

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Re: Two for one on hardware issues
« Reply #30 on: 22:57, 09 July 18 »
Try testing the output pins of the buffers mentioned above, but also the outputs of the multiplexers (74LS153's). All of these could could be the cause of the issue.

Bryce.


What should I look for? A specific voltage with a multimeter? Or do I need a fancier tool?

Offline Bryce

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Re: Two for one on hardware issues
« Reply #31 on: 09:27, 10 July 18 »
It's more difficult to be 100% sure with a multimeter, but you could at least check if any bits are "stuck": ie: any output that is always 5V or always 0V is suspicious. A changing bit will read a value somewhere in between (2V - 4V) depending on the ratio of 1's and 0's.A scope would obviously be a better choice of tool.


Bryce.
 

Offline walterg74

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Re: Two for one on hardware issues
« Reply #32 on: 03:34, 26 July 18 »
IC114 and IC115

Bryce.


Ok, FINALLY got a 74LS244 and a 74LS373 today (plus 2 sockets  ??? ).


Guess I will try replacing these two and see what happens...

Offline walterg74

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Re: Two for one on hardware issues
« Reply #33 on: 06:04, 29 July 18 »
IC114 and IC115Bryce.



Well, removed those two, soldered a pair of sockets and inserted replacements. Nada...


Same gray screen with black border  :(


Offline walterg74

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Re: Two for one on hardware issues
« Reply #34 on: 15:25, 06 August 18 »
Bumpity bump...


Getting a bit frustrating buying and replacing chips with no improvement :(


Do you think I should try the last thing replacing the 74LS153's ..?

Sometimes when turning it on I get something like the attached, but 95% of the time it’s just the grey screen with black border.


Anything else I may be missing..?  :'(

Offline walterg74

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Re: Two for one on hardware issues
« Reply #35 on: 15:26, 06 August 18 »
Another variant

Offline walterg74

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Re: Two for one on hardware issues
« Reply #36 on: 15:26, 06 August 18 »
And a third variant...

Offline Bryce

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Re: Two for one on hardware issues
« Reply #37 on: 20:38, 06 August 18 »
Bumpity bump...


Getting a bit frustrating buying and replacing chips with no improvement :(


Do you think I should try the last thing replacing the 74LS153's ..?

Sometimes when turning it on I get something like the attached, but 95% of the time it’s just the grey screen with black border.


Anything else I may be missing..?  :'(

Unfortunately you are trying to do a "blind repair" which often ends in disappointment and frustration. Normally you test first and change the required parts, but without proper test equipment, it's just taking educated guesses. Sometimes you get lucky and hit the jackpot with the first guess, but often it ends like this.

Bryce.

Offline walterg74

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Re: Two for one on hardware issues
« Reply #38 on: 21:20, 06 August 18 »
Unfortunately you are trying to do a "blind repair" which often ends in disappointment and frustration. Normally you test first and change the required parts, but without proper test equipment, it's just taking educated guesses. Sometimes you get lucky and hit the jackpot with the first guess, but often it ends like this.

Bryce.



Yes, that’s unfortunately the case. Don’t have any test equipment beyond a multimeter, but even so, it’s useless without the knowledge of what to look for. I do have a 464, but besides the CPU (which I did test anyway just in case), I don’t have anything else I can use it to test I think.
I was only going by the list detailed on another post for the observed symptoms. (40031,RAM, 244/373,etc.)


 Would you say if it stopped worked suddenly (in front of my eyes) that in theory it should be one component?


What would you suggest?


Thanks, Bryce.

Offline Bryce

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Re: Two for one on hardware issues
« Reply #39 on: 19:28, 07 August 18 »
Electronics almost always dies instantly in front of your eyes, it doesn't necessarily point at whether one or more components have died, because one failure can cause further failures within milliseconds. I'd suggest that if you really want it to work again, you should send it to someone to have it fixed. If you can't find someone local you can always send it to me.

Bryce.

Offline walterg74

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Re: Two for one on hardware issues
« Reply #40 on: 01:59, 08 August 18 »
Electronics almost always dies instantly in front of your eyes, it doesn't necessarily point at whether one or more components have died, because one failure can cause further failures within milliseconds. I'd suggest that if you really want it to work again, you should send it to someone to have it fixed. If you can't find someone local you can always send it to me.

Bryce.


Thanks Bryce, I understand.


Today I won an auction for a second 6128 that is in working order. I think with this I should be able to at least check the components more properly. Although of course it wouldn’t rule out things that can’t be tested with this method. And then I will just have to send it to someone who knows... (there is definitely nobody local)


While I am very far away, where was it that you are located?

Offline Bryce

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Re: Two for one on hardware issues
« Reply #41 on: 19:01, 08 August 18 »
Germany, but it shouldn't be too expensive if you just send the PCB.

Bryce.

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Offline walterg74

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Re: Two for one on hardware issues
« Reply #42 on: 00:58, 09 March 19 »
Hi All,


Posting back because I really hate when I see people asking things and then never posting back to say what happened / how things turned out...


I had gotten a second working 6128, and tried swapping the other non-standard chips with the same results...


I contacted someone I was refered to who was local, and had the expertise and proper tools to take a look at it. What they found was that simply some traces had been corroded under the mask (said probably humidity at some point?) and after they repaired them, the machine booted up normally again :)


When he sent me the pictures I first thought “how on earth did I not see this??” But then he told me it wasn’t visible but was under the mask  :D

Anyway, happy with my once again working 6128, and now I have two I guess :)


Thanks to all for the help!