1988 Macintosh II board.. Need help

9 posts / 0 new
Last post
Verault's picture
Offline
Last seen: 21 hours 43 min ago
Joined: Dec 21 2017 - 14:19
Posts: 190
1988 Macintosh II board.. Need help

So I have a Macintosh II board 338J from 1988. I received it with damaged traces and it was dead. I have fixed some bad traces and now I get the startup chime but that is it. It stop somewhere in the process before loading the floppy drive. No video ever even with known good cards.

 

I have been using these schematics to go over the traces but I really need a new set of eyes on this as I am beyong frustrated. 

https://ia801007.us.archive.org/0/items/Macintosh68kSchematics/Macintosh68kSchematics.tar.bz2

 

I have verified the data lines from all 4 roms to the VC2869 sound chip, the IWM, c8 (74Als651), D8  (74Als651), e8  (74Als651), VIA1, VIA2, 53c80 SCSI chip, Z8530 SCC chip, f8 (74Als651), the 68020 socket, MC68881 FPU socket, and the MC68851 PMMu socket. I have verified the RAM and roms work in another working MAcintosh II.

I did not try swapping the Sound chip or IWM (although I cleaned the contacts on the IC (would a bad IWM or Sound ic halt the bootup?).

 

edit:: I also verified the DATA lines from the 4 rom chips to the 8 ram simm slots...

 

I feel I am pretty close to resurrecting this board, please help!

 

 

Verault's picture
Offline
Last seen: 21 hours 43 min ago
Joined: Dec 21 2017 - 14:19
Posts: 190
So I learned two things. The

So I learned two things. The machine wont bootup (no startup chime) without the IWM and sound chip. I tested them on my second board and they work. I didnt think this was related just wanted to cover all my bases.

Verault's picture
Offline
Last seen: 21 hours 43 min ago
Joined: Dec 21 2017 - 14:19
Posts: 190
Anyone?!
Anyone?!
Offline
Last seen: 6 hours 45 sec ago
Joined: Feb 27 2021 - 18:59
Posts: 38
Mac II Diagnostics

You really don't give much to go on.

 

One thing you can do is to use the diagnostic port.

See the documentation at https://mac68k.info/wiki/display/mac68k/Diagnostic+Mode

(This is the firmware inside the machine that is controlled by the TechStep)

 

If you see *APPLE*..... on the serial output, you at least know the CPU is running. Then you can run tests to see if RAM and ROM is functional and test the VIAs etc.

 

One point to note on that page is what it looks like when the diagnostic port is activated.

When the system boots with this pin [VIA1 PA0] pulled to ground, the system will chime, but not display any video.

Isn't that what you're seeing? Check if that pad is shorted to ground on the board.

 

PS. Does this machine have the HMMU or the MC68851 PMMU installed? What capacity SIMMs are installed?

(Mac II and IIx are only compatible with PAL SIMMs above 1MB)

Verault's picture
Offline
Last seen: 21 hours 43 min ago
Joined: Dec 21 2017 - 14:19
Posts: 190
robespierre wrote:You really
robespierre wrote:

You really don't give much to go on.

 

One thing you can do is to use the diagnostic port.

See the documentation at https://mac68k.info/wiki/display/mac68k/Diagnostic+Mode

(This is the firmware inside the machine that is controlled by the TechStep)

 

If you see *APPLE*..... on the serial output, you at least know the CPU is running. Then you can run

 Hi Robespierre. I am sorry I am somewhat new to MAC repair so if I am not giving much to go on please be patient and tell me what Info would be helpful.

Right now the machine has a MC68851 but I have tried with both.

You say the II isnt compatible with simms smaller than 1mb but both of mine came with 4 X 256KB simms and 4 X 1MB simms. (keep in mind one works with 5mb, I am attempting to fix the other)

The pin in question on th bad board is not pulled down to gound.

 

This is the first time I have ever heard of TechStep so thank you very much for brining it to my attention. What is the easiest method for trying to read out info from the serial port to diagnostics as I obviously dont have a Techstep device.

 

 

Edit: Also wanted to add that grounding line PA0 of VIA1 (pin 2) on my working Mac II doesnt visibly do anything. I still get video and the machine boots up to the floppy prompt on screen.

 

 

 

 

 

Offline
Last seen: 6 hours 45 sec ago
Joined: Feb 27 2021 - 18:59
Posts: 38
Sorry, I meant that if the

Sorry, I meant that if the SIMMs contain 4Mbit DRAMs they must have a PAL. That isn't required on later machines (IIcx onward).

256KB and 1MB SIMMs are compatible.

 

OK, so the instructions to ground PA0 don't work. I'll test later on with my machine.

Do you get any data on the serial port? Try pressing the Interrupt switch shortly after power on?

Verault's picture
Offline
Last seen: 21 hours 43 min ago
Joined: Dec 21 2017 - 14:19
Posts: 190
robespierre wrote:Sorry, I
robespierre wrote:

Sorry, I meant that if the SIMMs contain 4Mbit DRAMs they must have a PAL. That isn't required on later machines (IIcx onward).

256KB and 1MB SIMMs are compatible.

 

OK, so the instructions to ground PA0 don't work. I'll test later on with my machine.

Do you get any data on the serial port? Try pressing the Interrupt switch shortly after power on?

This may sound like an odd question but what would be the easiest way of testing data from the serial port? A mini din serial cable (image writer II cable??) running to another working MAC? What do I run on the other machine? Sorry IF this seems remedial.

Offline
Last seen: 6 hours 45 sec ago
Joined: Feb 27 2021 - 18:59
Posts: 38
An ImageWriter II cable is a

An ImageWriter II cable is a null-modem cable, so it would work for connecting to another computer (DTE).

I usually use a Keyspan USB-serial adapter. I can recommend ZTerm if you use Mac OS (classic or modern).

The other common type of MiniDIN-8 serial cable goes to a DB25M wired for a modem (DCE). Combined with a gender changer and a null-modem adapter, you could get this hooked up to a PC serial cable attached to a PC. HyperTerminal is a widely used Windows communication program that should work. PuTTY is another.

Verault's picture
Offline
Last seen: 21 hours 43 min ago
Joined: Dec 21 2017 - 14:19
Posts: 190
Sounds good, let me play with

Sounds good, let me play with it a bit between my working MAC II and some random machine/console once I get that working I will see if anything is being output from the bad Mac II.

Log in or register to post comments