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Apple //c Diagnostic Test

oldpcguy

Experienced Member
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Sep 23, 2021
Messages
145
I have an Apple //c which, when the diagnostic test is run, indicated a problem with the main bank of memory. The test result displays a zero followed by a one and then five zeros:
.
0 1 0 0 0 0 0 0​

The one indicates the bad memory chip which I plan to replace. The problem is I don't know what order this display is wrt to the layout of the memory. Does the one represent bit 1 (F18 on the system board) or does it represent bit 6 (F13 on the system board). I can replace both chips but, given the price of these old chips, I'd rather not replace two when only one is necessary. Does anyone know how to translate this result into a chip location?
 
Last edited:

desertrout

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Jun 16, 2020
Messages
17
Yup - that number corresponds to chip #7 (well, 6 counting from 0). So, with the board oriented with the I/O's on the far side from (the same way the board is oriented when installed in the machine if the keyboard were facing you), and the RAM IC's on the right-hand side, count seven IC's up (or away) from you. Of, if you orient the board with the RAM IC's on the edge furthest to you, count seven IC's from the right. It should be labelled as MRD6 on the board

Note that these error messages aren't necessarily complete - the test only stops at the first bad chip. It's not uncommon for there to be several chips requiring replacement. There is also a possibility that the error is not caused in the RAM, but further up the address line.

The chips themselves shouldn't be that expensive... any 16 pin DIP 4164 or 4264 RAM will work, easy to find cheap on eBay, or even Jameco stocks them: https://www.jameco.com/shop/Keyword...d=10001&search_type_c=jamecoall&freeText=4164
 

oldpcguy

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Sep 23, 2021
Messages
145
Thank you for the information DT. I haven't had an opportunity to work on this further but hope to have some time in the upcoming days. I'll report back with my findings.
 

VERAULT

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use lots of flux. Whatever solder they used on the IIc's was terrible and it turned into crus after all this time. You can still buy the RAM chips online so cutting the legs off the old ram to pull out and socket is much easier than attempting to save the chip and Tearing traces. IF you were gonna tear traces on an apple II, the IIc would more than likely be the one its going to happen on.
 

desertrout

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Jun 16, 2020
Messages
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Oh man, so true. Getting the chips out can be fussy, requires a lot of patience. I usually have to add additional solder to mix in with that gungy old stuff to get it all out. Hopefully you have a desoldering iron, makes the job much saner - even one of the cheap ones. And getting a socket in there (low profile) is a good call. If the bad chips are limited to the main bank, then you shouldn't encounter any space issues... I think it's only an issue for those chips directly under the drive motor.
 

oldpcguy

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Sep 23, 2021
Messages
145
Oh man, so true. Getting the chips out can be fussy, requires a lot of patience. I usually have to add additional solder to mix in with that gungy old stuff to get it all out. Hopefully you have a desoldering iron, makes the job much saner - even one of the cheap ones. And getting a socket in there (low profile) is a good call. If the bad chips are limited to the main bank, then you shouldn't encounter any space issues... I think it's only an issue for those chips directly under the drive motor.

I use a rework stations hot air gun to remove the chips. Once the chip has been removed I use a solder pull-it to remove any excess solder from the holes (typically I need to add solder first)
 

VERAULT

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Hot air isnt going to help with that kind of through hole crud. Your going to need a thick pin or pick to clear out the solder that is now a crust. It just wont adopt new flux or new solder. That was my point.
 

oldpcguy

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Sep 23, 2021
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Hot air isnt going to help with that kind of through hole crud. Your going to need a thick pin or pick to clear out the solder that is now a crust. It just wont adopt new flux or new solder. That was my point.

That's what the solder pull-it is for. It works great for clearing out the holes. I've used this procedure to replace about half a dozen 16 pin DIP DRAM chips without any damage to the board.
 

oldpcguy

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Sep 23, 2021
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I dont think Im getting my point across. Good luck.

Perhaps not but I think I understand it. You think that, after using the rework stations heat gun, that it will look like this (this is the actual work I did to remove the chip in question and is not an example):

Bottom:

20211215_152733.JPG
Top:

20211215_152337.JPG
You are correct that solder is still in the pin holes preventing a new chip from being inserted. In order to correct that I use a solder pull-it to remove it. Here are the results:

Bottom:

20211215_154104.JPG
Top:

20211215_154038.JPG

Here is the new chip inserted after the solder was removed with the solder pull-it:

Bottom:

20211215_154432.JPG
Top:

20211215_154329.JPG

All that's left to do is solder the new chip in place.

Old chip which is still useable should an incorrect chip be removed:

20211215_154008.JPG
 

VERAULT

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Im with you on keeping the good chips regardless of brand. They arent making any more anyway. I use a rigid 2 inch long pin to open eyelets. IT try to get as much solder out of the hole and insert the pin. I heat it up with the iron to push it futher in. When it cools I pull it out. Works most of the time.
 

oldpcguy

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Sep 23, 2021
Messages
145
While I like to keep the removed chips intact in the event I may need them it's definitely a secondary concern compared to damaging the system board. If I do many more of these I think I'll invest in a de-soldering station.
 

VERAULT

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well my advice on that is dont skimp. Due to many recomendations from this forum i bought a hakko fr-300. it wasnt cheap but i use it all the time and its well worth it. unfortunatwly they released the fr-301 a couple months after i bought it but everyone i know who has one loves it.
 

oldpcguy

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Joined
Sep 23, 2021
Messages
145
well my advice on that is dont skimp. Due to many recomendations from this forum i bought a hakko fr-300. it wasnt cheap but i use it all the time and its well worth it. unfortunatwly they released the fr-301 a couple months after i bought it but everyone i know who has one loves it.

Thank you for the recommendation. It looks like I can purchase the 301 from Amazon for $251. Is that a good price?
 
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