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Macintosh IIsi blue screen - need help

9166188

Well-known member
Hello Fellows!  

I got a IIsi from ebay.  It shows a blue screen on a 13" Apple High Resolution monitor when powers on.

After some frustaration, I added a new PRAM battery and replaced all 47uF caps, but not the big caps yet.  But the result is all the same except the PSU can be switched off by the power button (previously, it refused to turn off unless unplug.)

Another strange thing is the RAM slots:

<a> if the 2 slots near to the PRAM battery is filled with RAM, this boots with a single chime + blue screen

<b> if the other 2 slots or all 4 slots are filled with RAM, this boots with a single chime followed by a death of chime melody + blue screen 

To avoid the death of chime in <b>, right now I put only RAMs on the 2 slots near the battery, but the blue screen problem remains as in (a)

Its hard disk is good because I tried it on another Mac.

Some suggestions would be much appreciated as I run of of tricks.   

Best!

Ken

 
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bibilit

Well-known member
IIRC all slots should been filled and with the same amount of Ram.

Also, no Pram battery is needed to get it going, so your problem is not here.

Last, IIsi PSUs are prone to failure, what outputs are present ?

 

Trash80toHP_Mini

NIGHT STALKER
Yep, all four slots need to be filled and matched.

You didn't say you'd tried it with no RAM SIMMs in the Bank B slots, what result to you get in that configuration?

 

9166188

Well-known member
"Last, IIsi PSUs are prone to failure, what outputs are present ?"  Only a blue screen without anything on it.  The PSU seems to be working: LED on, fan and hard disk spins.   

Where is Bank B?  

Suppose IIsi RAM slots layout:

(empty ROM SIMM)

1[        ]

2[        ]

3[        ]

4[        ]

(PRAM battery)

-> Single Chime w/ blue screen: Ram in (3) or (3,4)

-> Death of Chime w/ blue screen: Ram in (1), (2), (4), (1,2) or (1,2,3,4)

-> No chime: no RAM presents

 
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Trash80toHP_Mini

NIGHT STALKER
Sorry, that wasn't quite clear. Bank B would be the SIMMs, Bank A is the soldered DRAM ICs on the MoBo.

No RAM in any of the slots would be the stock configuration of the IIsi. RAM expansion requires matched SIMMs in all four. So you can stop testing with combinations of SIMMs

You only have two states to test.

1) all four slots empty

2) all four slots populated with matching SIMMs

 
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9166188

Well-known member
Just gave it another test: without any RAM in slots, it's also death of chime w/ blue screen.

So what does this all mean?   Does it look like RAM slot problem or something unrelated?

-> Single Chime w/ blue screen: Ram in (3) or (3,4) 

-> Death of Chime w/ blue screen: Ram in (1), (2), (4), (1,2) or (1,2,3,4) or empty slots

 
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bibilit

Well-known member
The PSU can produce the 12v and 5v required for HD but - 12 v should be present also.

The connector on the motherboard, viewed from the top. The back of the
machine is on the right side of the connector.

+--+--+--+--+--+
|1 |3 |5 |7 |9 |
+--+--+--+--+--+
|2 |4 |6 |8 |10|
+--+--+--+--+--+

1: +12V
2: GND
3: +5V
4: GND
5: +5V
6: -12V
7: +5V
8: PWR ON *
9: GND
10: SBY 5V

* The power on signal is a short positive voltage pulse

Also, have you washed the board ? replacing capacitors is ok, but goo can be present...

 

9166188

Well-known member
How to test the 12V?   I suppose I can wire up [PWR ON] and a [GND].   And then power on to test [12V] against any [GND] by a multimeter?

BTW, where did u get the PSU pinout from?   I opened the IIsi PSU, but the pinouts seem to be different from yours.   But I am not familiar with this stuff.

My topdown view after opening the top cover:

-----------------------------------------------------------------

[ Orang| Red   | Red     | Red   | Black  ]

[ Black | Black | Green | White| Yellow ]

                                                                                       ] [ Power Plug = = = =

-----------------------------------------------------------------

 
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9166188

Well-known member
I am not sure how to measure the PSU for 12v directly because the power on button of IIsi is on the motherboard.

But I did take measure of the hard disk cable and successfully read 12v from its orange cable and 5v from its red. Can this suggest the PSU is quite healthy?

Btw, I washed the motherboard.

Any suggestions?

image.jpeg

 
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9166188

Well-known member
Can anyone share whether IIsi can boot without Death of Chime with onboard RAM only?   I want to rule out RAM or RAM slots related problems.   Thanks! 

 

Trash80toHP_Mini

NIGHT STALKER
Yep, as I said above, you can test it only two ways:

Boot it with just the 1MB on the board (the standard memory config for the IIsi) or test it with four identical SIMMs installed.

No other possibilities exist.

 

9166188

Well-known member
Thanks!  As said, with only 1MB onboard RAM, it gives blue screen and death of Chime.   I am none of the wiser what the problem would be except it probably not due to PSU.

Would it be this is a rare Mac that requires an ROM SIMM card?   How can one tell whether this machine has a onboard ROM or not?

 

bibilit

Well-known member
Rom chips are in the lower right side of the board.

http://ep.yimg.com/ca/I/lovemacs_2445_68416481

IIRC there is a jumper also to select the Rom simm or chips. 

Don't think is your issue, the fact that the board is giving you a chime won't probably work if the Rom was missing.

Your problem is probably coming from the logic board, a damaged trace or something related...

 

9166188

Well-known member
Thanks a lot @bibilit !  Interestingly, the ROMs are there.  I think your diagnosis of the logic board makes sense.  

 

bibilit

Well-known member
i will wash the board if not been done yet and have a close look at the board, the battery never had any issue in this computer ?

The IIsi is a very nice machine, i don't see much units for sale, maybe someone here has a spare board for sale/trade ?

 

9166188

Well-known member
Yes, it was washed and the battery is new.  My last rescue attempt will be to change the remaining two large caps and perhaps another bath.   After that, hunting for a new mb on ebay.

Will let you and @NIGHT STALKER know if it works.   Thanks both of you for ideas and support!   :)

 

9166188

Well-known member
Can anyone tell me what diode (labeled DZ1) to order? Or can anyone provide a good resolution snapshot of the diode chip? Thanks!

image.jpeg

 
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techknight

Well-known member
Thats not likely causing your problem. What do you mean seams faulty? 

I honestly think you have a broken trace somewhere from cap goo. 

 
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