[SE30] Repair in progress

[Sebastian]

Recently i acquired an SE30 from a colleague:

After a brief inspection of the board for battery damage (no damage!) I hooked up the power and switched it on:

Uh-Oh...

Nice pattern for my wallpaper, but for a system a bit unpractical. Also i could very faintly hear the 'chime of death'. I replaced the caps and washed the board:

Reassembled the Mac and i got exactly the same onscreen but with a louder sound:

Youtube video[/]

 

Using schematics, tracing every line in the video-system:

 

 

Even with no processor, ROMsimm, RAM or video-rom the pattern was the same. I then knew my problem was probably with the video-ram adress muxes or the RAM itself. The muxes are really cheap (about 40 cents a piece), so i removed them. My theory is that without them only the first byte of video-ram would be used on screen (and repeated in horizontal and vertical direction)

 

 

After removal of the muxes i got this:

 

 

As you can see there is a different pattern now. The weird thing is that it should be solid white and black bars, no intermission because the RAM is empty!

 

Now i suspect the videoram, i've removed the chips and ordered a bunch on Ebay. Now i wait...

 

 

I don't expect the Mac to be fully operational after this repair, but perhaps it will give me another hint on how to repair it when the video is working properly.

 

To be continued!

 

[Ike]

Cool, this is hard-core!

I'm curious what it does without the videoram.

The SE/30 is a bit weird in the sense that it outputs video from the VRAM to the screen as soon as power is applied right?

I think its still a bit odd that it gives you a chime of death after the recap, or is that because of the missing RAM?

Veel succes

 

[uniserver]

good job… keep up the good work… i would like to think there is a light at the end of the tunnel for your project.

did you tone out the RAM slots? slots 1 and 2 (bank one)

 

[Sebastian]

Cool, this is hard-core!
I'm curious what it does without the videoram.

The SE/30 is a bit weird in the sense that it outputs video from the VRAM to the screen as soon as power is applied right?

I think its still a bit odd that it gives you a chime of death after the recap, or is that because of the missing RAM?

Veel succes

Without videoram the inputs are floating and give lots of 'static' lines etc. The SE30's videocircuit is to be blunt quite dumb. It just starts reading the videoram and puts it on screen.

Dank je wel

 

[uniserver]

have you seen this?

Amiga 500+ corroded motherboard repair - battery leakage

http://www.youtube.com/watch?v=Aj0Qbrs_3Gk

 

[Ike]

Without videoram the inputs are floating and give lots of 'static' lines etc. The SE30's videocircuit is to be blunt quite dumb. It just starts reading the videoram and puts it on screen.

Very interesting.

Well, at least the SE/30 has dedicated VRAM to begin with

P.S. Oh yeah Uni you sent me one of his videos too, love 'em, watched a whole bunch!

 

[uniserver]

hey could you guys too me a favor and ask him to repair some dead se/30's or dead 840av's ?

I asked him and he ignores me.

 

[Ike]

HEY :-/ Just came across something...

Your chime of death sounds weird. It has the sharp two extra tones in it.

now

also shows your death chime out of a IIciCould this help diagnosing a certain problem?

Also sorry if I'm spamming your thread.

 

[Sebastian]

hey could you guys too me a favor and ask him to repair some dead se/30's or dead 840av's ? I asked him and he ignores me.

Huh?

 

[uniserver]

http://www.youtube.com/user/RetroGameModz?feature=watch

-- i think it would be cool to see how he goes about it.

 

[dougg3]

HEY :-/ Just came across something...Your chime of death sounds weird. It has the sharp two extra tones in it.

now

That's my video, and good catch! I went back through some disassembly and as far as I can tell, the extra sharp tones indicate that it's a RAM test failure. Both the single sharp tone and the two sharp tone sounds happen if the RAM test fails. I can't figure out what the difference is between the two of them though. Maybe high versus low bank or something like that?

It's possible that diagnostic info may be available over the modem port to give more information.

 

[TheMacGuy]

Well, if it was just the RAM, wouldn't it give a Sad Mac and error code instead of lines?

 

[dougg3]

That's a good point--more is probably wrong. All I'm saying is that I believe the sound before the chimes of death indicates that the RAM test is failing for one reason or another.

 

[Sebastian]

HEY :-/ Just came across something...Your chime of death sounds weird. It has the sharp two extra tones in it.

now

I've ordered a usb-serial gizmo, will try the diagnostics as soon as it arrives (well, not exactly, i still have to wait for the VRAM...)

But something seems a bit strange, the diagnostic-mode is triggered internally, on the PA0 line of VIA1. But what triggers the whole Techstep diagnostic system? How does it work? I really wish i had access to one of those and reverse engineer the system so we can use it for all our old Macs

 

[dougg3]

I think that the TechStep is able to signal to the Mac to enter diagnostic mode through a different mechanism -- probably either the SCSI port or a keystroke. The PA0 entry method would probably make more sense to be used for factory burn in tests...

 

[Sebastian]

I think that the TechStep is able to signal to the Mac to enter diagnostic mode through a different mechanism -- probably either the SCSI port or a keystroke. The PA0 entry method would probably make more sense to be used for factory burn in tests...

Still: we need to acquire a Techstep and analyze the heck out of it. Makes life easier for everyone

 

[dougg3]

Oh definitely. It would be awesome to make a little device that could do the same thing for much cheaper

 

[Ike]

It's possible that diagnostic info may be available over the modem port to give more information.

Ok that's amazing, never knew that a mac could do that.

as for how the TechStep does enable the troubleshooting mode, that could be as easy as just sending "HELLOMACIMTECHSTEP" to one of the serial ports, since it has to communicate with the ROM anyway, everything an be done softwarematically.

 

[techknight]

However diagnostic works, it has to be programmed in such a way that it cannot use RAM for any of its operations. it has to be ROM only, otherwise how would you run diagnostics if you had bad/missing RAM.