Mac SE/30 with strange SimasiMac - help needed

[bobo68]

Hi,

I acquired an SE/30 some time ago and it worked but started to show first symptoms of SimasiMac. Some weeks ago I gave it to a friend who has good soldering skills to do the recap. I gave him just the mainboard with everything removed.

When I got the board back and installed it, the SE/30 greeted me with this SimasiMac "on steroids":



The Mac shows the mouse pointer, I can move it and it shows the flashing "give me a boot disk" question mark. The pattern looks like a combination of the jail bar pattern and a checkered flag.

I decided to replace all caps again (this time I used tantalums, except from the big axial types of course). I recognized that my friend had ripped one the pad of C6 (plus side). I connected the plus side of the cap with pin 7 of chip UB11 with a wire. Still I got the same symptoms.

I then thoroughly washed the board and inspected all chips for blobs of solder and reseated the ROM chips and RAM. No change. I visually checked the underside of the board: all clean and well. I tested all caps for correct connection to ground or the respective other parts of the board. Everything seems normal apart from C1 where my multi meter shows a resistance of 500 ohms on both pins (to ground and Pin 12 of J12). I used the replacement and pinout jpeg posted on this board and Apple's schematics as a reference.

So now I'd like to ask the experts if they recognize this kind of SimasiMac. What is the cure or what can I do to further diagnose the problem? I have a scope and multi meter.

Any help is much apreciated.

Best, bobo68

 

[uniserver]

your problem is going to be in this area some where.



in the from of something rotted from cap goo.

- trace

- via

- Pad I/c is connected to

- something under one of the I/C's

 

[bobo68]

Ok, will have a closer look. I forgot to mention that the startup sound is also distorted.

 

[uniserver]

****

also read this thread.  https://68kmla.org/forums/index.php?/topic/20541-se30-horizontal-sweep-linesstill/page-3

 

[uniserver]

Sound being distorted is probably something under the ASC.  Witch is right there near that red circle in the image.

cap goo likes to creep under I/C's and rot.  it's unpleasant really. 

 

[bobo68]

Where is the ASC relative to C7 on your picture?

I thoroughly cleaned the board with isopropanol and later also water + dishwasher (and let it dry). Do you think there can still be some goo left?

 

[uniserver]

( and let it dry )  --  

i would make it dry with an air compressor.

blast all the water out of all the nooks and crannies.

the issue right now, is past shorting from cap goo,

the issue right now is damage that has been done from the cap goo.

so its going to require some repair at this point, by running patch wires, more then likely.

ASC is in yellow

 

[techknight]

If the sound is distorted, you have a broken data/address line, which probably also feeds the video circuitry which is right there. 

So, you need to grab the SE/30 schematics, and test ALL address/data lines from that IC, against the ROM socket. The break is likely right above the power jack below the SCSI/SCC

 

[bobo68]

Hi techknight,

just to be absolutely sure: what do you mean with "that IC" and "ROM socket"? The ASC and the ROM SIMM?

Best, bobo68

 

[bobo68]

I did some connection testing in the areas you mentioned. Not completely but like in thread https://68kmla.org/forums/index.php?/topic/20541-se30-horizontal-sweep-linesstill/page-3 I found that A0 line between UD8 and UK6 (Video ROM) has no connection. The Oother address lines from UD8 and UE8 do connect to UK6.

Furthermore I tried other A0 connections and found them also to be broken between UI8 (GLUE) and UE10 (ASC). A1 is connected. Same between UD8 and UI8 (A0 broken, A1 ok).

Is this a pattern you recognize? Maybe there is a central point where it should be fixed.

 

[techknight]

Follow the schematic, if theres a break where there should be a connection, run a patch wire and test again. 

 

[bobo68]

Sure I can do it the pedestrian way. I was hoping somebody has seen this combination of video and audio failure and there is a central point where it can be fixed.

I have a hard time understanding how the connections run across the 9 pages of the schematic. I cannot find any markers which allow me to stitch together the whole schematic.

That said, is e.g. an address line supposed to be connected across the whole board? e.g. A1 can be found on many chips, do they all directly connect or is there an intermediary between them (the GLUE?)?

Where are lines VADR supposed to go? They can be found on UA8, etc.

 

[techknight]

A0/A1 is only located on a few chips. Most of the bus starts at A2+

 

[bobo68]

Ok. Connecting the A0 address line between UD8 and UK6 brought the video back without any jail bars etc. Woohoo. Now comes the sound...

 

[techknight]

I figured it would

 

[bobo68]

Do you know if UE10 (ASC) should be directly connected to UI8 (GLUE)? I can see a trace between them that looks super good but still no connection on the A0 line.

Or should I go from UE10 to UK6 (Video ROM)?

 

[techknight]

I believe it does go to the GLU. But I cant remember. If the schematic shows there is an A0 present, then its likely broken. 

 

[bobo68]

I decided to connect UE10 and UI8 directly. It worked, the little sucker now has video and sound. Nice! Thanks for your support.



So this one will get an Ethernet card as an award later and I have another SE/30 waiting for the recap.   And a IIci. 

 

[Westinghouse]

Nice work!