Re: Troubleshooting X/Lisa RAM boards - first draft from simon on 2011-03-27 (lisalist1)

From: simon <simski_at_email.domain.hidden>
Date: Sun, 27 Mar 2011 11:08:30 +0200

use a socket for the chip. resoldering double layer boards wrecks them a bit. even with a reflow station. On 26 mrt 2011, at 23:15, Terry Stewart wrote:

> James,
>

>> Bit 0 maps to column 22 on the memory board, so the suspect chip is the one at coordinates E22. (If that isn't it, I think the only other possibility is B22.)

> 
> You were right on the button here!  I piggybacked a 4164 over the IC at  E22 and the board passed the memory check with no problems.  It seems that's the faulty one allright.  Later today I'll extract and resolder a replacement in.
>

>> I think the four possible slot combinations might give different results, so try each configuration with the bad board:
>> - in MEM 1 with MEM 2 empty
>> - in MEM 2 with MEM 1 empty
>> - in MEM 2 with a good board in MEM 1
>> - in MEM 1 with a good board in MEM 2

> 
> In a few minutes I'll run these tests with the second board and post up the results.  Stand by..
> 
> Terry
> 
> ----- Original Message ----- From: "James MacPhail" <gg__at_email.domain.hidden>
> To: <lisalist_at_email.domain.hidden>
> Sent: Saturday, March 26, 2011 3:19 PM
> Subject: Re: Troubleshooting X/Lisa RAM boards - first draft
> 
>

>>> One USED to come
>>> up with a parity error.  Now it doesn't even get that far.  Instread I get a
>>> checkerboard pattern so there might be more than one chip faulty on this
>>> one.

>>
>> I think the four possible slot combinations might give different results, so try each configuration with the bad board:
>> - in MEM 1 with MEM 2 empty
>> - in MEM 2 with MEM 1 empty
>> - in MEM 2 with a good board in MEM 1
>> - in MEM 1 with a good board in MEM 2
>>
>>

>>> The second board comes up with a read/write error.   Using just that one
>>> board in memory slot one I examined the words at the place indicated and
>>> found..
>>> 
>>> 00000186 0000 0000 0000 0001 0000 0000 0000 0000
>>> 
>>> Using your rule of thumb, this would seem to be Row E, yes?

>>
>> Yes, that's correct (I hope).
>>

>>> translate this to exactly which bit this is and also what column?  I do
>>> know what binary is and how it (and hex) translates to things regarding
>>> 8-bit but not really at the chip level .  Are you able to elaborate (or
>>> point me to a URL) on how this is translated?  I assume these words are in
>>> hex?  I assume so if you can get something like 4000.

>>
>> Yes, the words are in hex. Each character of the four in one word is one hex value, from 0 to F, and those correspond to the 16 possible binary values of 4 bits.
>>
>> The bit positions are (sometimes) numbered, with bit 0 being the least significant, and rightmost bit. Your value of 0001 has the rightmost bit set, and that is bit 0.
>>
>> Bit 0 maps to column 22 on the memory board, so the suspect chip is the one at coordinates E22. (If that isn't it, I think the only other possibility is B22.)
>>
>> I know that's not a clear explanation of the bit numbers, but perhaps will suffice.
>>
>> If there is just one bit set (ie. only one bad chip), then there are 16 possible values for the word, which map to memory board columns as follows:
>>
>> Word Bit# = Column
>> ---- -- --
>> 0001 0 = 22
>> 0002 1 = 21
>> 0004 2 = 20
>> 0008 3 = 19
>> 0010 4 = 18
>> 0020 5 = 17
>> 0040 6 = 16
>> 0080 7 = 15
>> 0100 8 = 1
>> 0200 9 = 2
>> 0400 10 = 3
>> 0800 11 = 4
>> 1000 12 = 5
>> 2000 13 = 6
>> 4000 14 = 7
>> 8000 15 = 8
>>
>> If there is more than one bad chip, there will be more than one bit set, and you'd get a character other than 1,2,4,8, or more than one in the word.
>>
>> Good luck!
>>
>> James
>>
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> 
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--
Groeten,

Simon
simski_at_email.domain.hidden

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Received on 2015-07-15 16:53:21