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#26 2014-08-02 03:38:37

techknight
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Registered: 2014-05-22
Posts: 449

Re: Garbled screen on portable

I wonder if the RAM itself is bad. hmm..

Do you have an expansion card? You could also try pulling the SWIM.

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#27 2014-08-02 09:22:31

max1zzz
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Registered: 2014-05-18
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Re: Garbled screen on portable

Yes i have a expansion card, the portable acts the same with and without it

I'll pull the swim off it later and see how it acts

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#28 2014-08-03 14:58:08

max1zzz
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Re: Garbled screen on portable

Ok pulled the swim, and it dose the exact same thing, sadmac 00000005

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#29 2014-08-03 16:49:18

techknight
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Posts: 449

Re: Garbled screen on portable

then you definitely have a for sure break somewhere, or in the rare event one of the SRAMs is bad.

If you have some time to waste, you could try swapping the banks around and see if the error code shifts banks. If so, you got a bad chip.

Last edited by techknight (2014-08-03 17:04:30)

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#30 2014-08-03 19:01:41

max1zzz
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Re: Garbled screen on portable

Hmm, i'm betting there is a break aswell, i guess i just follow each trace from the ram back to the processor till i find the break

I don't fancy swapping the banks, for the £20 it would cost i might aswell order new chips then i know they are all good, but i'll only do that if there are no breaks

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#31 2014-08-04 00:59:38

techknight
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Registered: 2014-05-22
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Re: Garbled screen on portable

Well all address lines end up at the 74 chips above the processor.

All the data lines end up at the two buffer ICs above the ROM, and then from there via 47Ohm resistors to the processor.

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#32 2014-08-04 09:32:31

max1zzz
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Re: Garbled screen on portable

Ahh right that makes it easy, do you know what order the address lines are in on the 74 chips?

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#33 2014-08-04 13:53:13

max1zzz
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Re: Garbled screen on portable

The plot thickens, all the address lines are good up to the 74 series IC's above the CPU

Data lines are next to be checked.....

Edit: Data lines are good up to the chips above the ROM Chips, Which pins on the processor should i now be checking from the chips to?

Edit 2: Not sure if any of this is useful, but when i removed one of the ram chips (U1F, which is the fifth chip down on the Left Side) the sadmac changed to 0000000E (Major) 0000FF00 (minor), Also at one point i removed the bottom Right RAM chip to cheack some traces, With that chip missing the portable gave me a reboot loop

Last edited by max1zzz (2014-08-04 15:02:36)

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#34 2014-08-05 00:42:32

techknight
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Registered: 2014-05-22
Posts: 449

Re: Garbled screen on portable

Yup. the beginning of RAM has to be good in order for the sad mac code to execute properly. If any of the RAM cannot be accessed correctly, itll go into a bootloop due to the fact the interrupt vector table in RAM is screwed.

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#35 2014-08-05 00:43:04

techknight
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Registered: 2014-05-22
Posts: 449

Re: Garbled screen on portable

We may in fact rule out the RAM, because 05 is external RAM addressing failed.

Almost as if it sees an external card present but its not. Strange... I still think there is an open trace somewhere you cannot see. Look by the 12V inverter, one of the RAM chips run close by there. there is a tank farm of caps that leak and might cause an issue with trace.s

Last edited by techknight (2014-08-05 00:45:14)

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#36 2014-08-05 00:57:24

max1zzz
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Registered: 2014-05-18
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Re: Garbled screen on portable

Hmm, ok will focus on there tomorrow

Seems odd that it is saying that it is failing to address external ram even with a ram card installed, but then i guess that would make sense if there are bad traces

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#37 2014-08-05 01:01:10

techknight
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Registered: 2014-05-22
Posts: 449

Re: Garbled screen on portable

I think there is a stuck address line, or a broken trace. But it could still be a bad RAM IC. bad RAM can do strange stuff. RAM still has to run the code for the mac to run diagnostics. if any of the code gets corrupt in RAM, well ya know...

I know you probably dont want to put a whole lot of effort in it, but you may have to strip everything off in the target areas and inspect things. I had to several times.

Last edited by techknight (2014-08-05 01:01:53)

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#38 2014-08-05 01:09:22

max1zzz
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Registered: 2014-05-18
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Re: Garbled screen on portable

Well it it's whats needed i'll do it, i probably couldn't afford to replace the MLB. (it's not removing chips that i don't like, it's resoldering smt chips by hand that isn't my cup of tea...)

Just a thought, could the 74 series chips the address / data lines run through be bad? Those are cheap to get so i might as well change them if they could be bad

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#39 2014-08-05 01:36:12

techknight
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Registered: 2014-05-22
Posts: 449

Re: Garbled screen on portable

its possible, but unlikely. 74 series logic dont go bad unless it was hit with gross overvoltage. A good way to check for that is measuring diode check resistance between all lines to ground. Anything that appears as a short, check to make sure it actually IS grounded, and if not then it could be bad.

Last edited by techknight (2014-08-05 01:36:55)

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#40 2014-08-05 16:55:25

max1zzz
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Registered: 2014-05-18
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Re: Garbled screen on portable

I'm intrigued as to why one of the ram chips seems to change the sad mac error, the fifth chip down on the left side make the error change from 00000005 to 0000000E No other chip seems to do this (I either get 00000005 or a reboot loop with any other chip removed)

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#41 2014-09-13 22:18:14

techknight
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Registered: 2014-05-22
Posts: 449

Re: Garbled screen on portable

ok, I got this board in to me.

it was giving me an 000005 code. So I decided to remove ALL of the RAM. Found an open chip-enable line going back to the MISC GLU.

As I suspected. I reinstalled All the RAM. Fixed the trace. Now I have a Sad Mac all 000000000000000.

Everything else is good. I think the RAM itself is bad on top of the open connection.

Also, when you re-solder chips back in place, be careful! the solder job is nearly awful and shorts started to develop so that wasnt helping matters any. Time for some training ;-)

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#42 2014-09-13 22:28:23

max1zzz
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Registered: 2014-05-18
Posts: 207
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Re: Garbled screen on portable

Awesome smile So how much is new ram going to set me back? (interestingly this is the third of forth mac from the Norfolk lot with bad ram, guess being in a uninsulated shed is hard on ram...)

And yeah... some all of that was pretty crap. Still find these fine pitch things tricky to solder, but i'm getting better at it, the work on my IIx board looked allot better.

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#43 2014-09-13 23:33:55

techknight
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Registered: 2014-05-22
Posts: 449

Re: Garbled screen on portable

I have to go through 1 chip at a time to figure out which one is bad.

Only way to know is build an SRAM tester. ;-)

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#44 2014-09-13 23:50:25

techknight
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Registered: 2014-05-22
Posts: 449

Re: Garbled screen on portable

Where is the patch wire at, where you made it stop giving random sad mac errors? I dont see any patches at all.

Last edited by techknight (2014-09-13 23:50:41)

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#45 2014-09-14 00:04:48

max1zzz
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Registered: 2014-05-18
Posts: 207
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Re: Garbled screen on portable

Ok, let me know how you get on there smile

Oh, i removed that a while back to see if it actually made any difference (which it didn't) and forgot to put it back on. It was a via right above the right keyboard connector (and just to the left of the tank farm there). Wasn't the best patch anyway, was needlessly long as i chose "easy" points (one pin of the powermanager IC to a resistor miles away.)

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#46 2014-09-16 18:29:32

max1zzz
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Registered: 2014-05-18
Posts: 207
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Re: Garbled screen on portable

any news?

Can't wait to (fingers crossed) see it running finally smile

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#47 2014-09-16 21:07:47

uniserver
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Registered: 2014-05-15
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Re: Garbled screen on portable

ya gotta let techknight work at his own pace smile
Just give him what he needs, and let em do what he does, he is a man that goes at his own pace.


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#48 2014-09-16 22:02:22

max1zzz
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Registered: 2014-05-18
Posts: 207
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Re: Garbled screen on portable

Yeah i know, he can take all the time he wants smile

Just eager to see this working (and i know this is gonna take some time, as he's gonna have to test all 32 chips...)

Not trying to hurry him in any way, just intrigued as to if he has found anything new

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#49 2014-09-17 00:28:08

techknight
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Registered: 2014-05-22
Posts: 449

Re: Garbled screen on portable

It took me 3 hours to pull and remount them all in the first place. Not looking forward to removing them all again. I havent had time, or been eager to jump back to it again. I actually got slammed with work this week, which is odd. its been slow the last couple months which allowed me to get most of this stuff done in the first place.

Last edited by techknight (2014-09-17 00:29:45)

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#50 2014-09-17 07:18:37

max1zzz
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Registered: 2014-05-18
Posts: 207
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Re: Garbled screen on portable

Ahh ok fair enough, I wouldn't be too eager to do that either.

I did consider just replacing it all, but 32 62256's are a tad on the expensive side....

thanks again for taking a look at it smile

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