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Macintosh SE/30 Faint chime and no video, possible short on +5V
Posted by: Ferrix97 on 2015-07-24 08:42:11
Hello

The Analog board is OK, I used another SE Board to test it and it works fine, I also installed the board in another SE/30 and it still shows the same issue: faint chime and no video (screen is totally black)

This seems to be a very early revision board, with the yellow-band capacitors.

I was looking at UE8 and I noticed that the resistance between +5V and GND is about 56 Ohms, which seems too low.

I then removed the capacitors and washed the board, now the resistance on J12 and UE8 is about 35 Ohms.

Soon I will solder new capacitors on the board, and measure the resistance again.

after washing the board (with the old caps still in place) The board produced a very faint chime, reset and interrupt also worked: I could hear the chime when I press reset and the sad mac tone when I press interrupt.

Once I recap the board, I will connect it to a Floppy drive and I'll see if it trie to read it.

Before I started working on the board, I took some photos, here are a few of them

IMG_4320.JPG

IMG_4321.JPG

IMG_4322.JPG

IMG_4323.JPG

IMG_4324.JPG

IMG_4325.JPG

IMG_4326.JPG

IMG_4327.JPG
Posted by: TheWhiteFalcon on 2015-07-24 09:26:55
Likely both bad caps and damaged traces. The UE8 section looks more than a little gunky.
Posted by: Ferrix97 on 2015-07-24 09:46:13
Update!

just finished the recap, now the chime is loud and clear.

It seems like the machine is not booting from its hard drive

looking at the floppy port, +5 is 5.00V, +12 is 12.23V but -12V is 0.03V.

EDIT:

I hooked up an external SuperDrive with a copy of the NAD in it, apart from the "blip" that makes after you turn on the system, it does nothing.
Posted by: Ferrix97 on 2015-07-24 10:41:25
I just so happen to have it's original user manual, that also includes pinouts of the various connectors.

It seems like the -12V is not present on this model, so all of the voltages are OK.

I have no idea why it chimes but doesn't boot
Posted by: uniserver on 2015-07-24 10:52:05
sounds like might be a bad floppy bourns filter, or bad scsi chip.. or bad lines to the scsi i/c.
Posted by: Ferrix97 on 2015-07-24 11:22:56
But even if the filters (which I have some of them in stock) and/or the SCSI IC are bad, the system should still show something on the display, right?
Posted by: uniserver on 2015-07-24 12:17:51
nope. just a grey screen, with a mouse pointer, if the filter is bad.  or if no screen at all .. then that means UE8 is fried.
Posted by: Ferrix97 on 2015-07-24 12:20:11
the display remains totally black

I can borrow a hot air station from a friend, what is the best way and temperature to remove the chip?
Posted by: uniserver on 2015-07-24 12:25:45
I set my hot air station at 575F

flux and tweezers? - not sure if that was your question.
Posted by: Ferrix97 on 2015-07-24 12:30:18
perfect!, thanks!

does the system start up if I only supply +5V using my bench power supply?
Posted by: max1zzz on 2015-07-24 12:35:18
I can't talk for the se/30 specifically, But I suspect it will, I know the LC will start up with only the 5v supply
Posted by: Ferrix97 on 2015-07-24 12:51:18
took a quick look at the schematics: it looks like it needs at least +12V and +5V, -5V and -12V are used only on a few (serial?) chips and on the expansion slot
Posted by: 360alaska on 2015-07-24 13:03:27
It doesn't need -12v to boot but it does power the sound amplifier setup so you would get any internal sound...
Posted by: techknight on 2015-07-24 14:48:49
the low ohms on 5V is actually normal, its the combination of the CPU and PALS loading down the 5V supply. 
Posted by: Ferrix97 on 2015-07-31 08:31:23
Update, I replaced UE8 (and lifted a pad in the process of doing it) but the problem is still there.

I repaired the lifted pad and all of the connections seem to mach the ones on the schematic.
Posted by: uniserver on 2015-07-31 12:02:50
Wow looks like you have a couple of problem se/30's.

where are you getting your UE8 from?   LC166 or HC166?

these things go bad a lot.  so sometimes, you can take one from a "parts" board,  and its actually already bad.
Posted by: uniserver on 2015-07-31 12:09:40
also swap your video rom with the other board just for giggles.
Posted by: Ferrix97 on 2015-07-31 12:18:24
The video roms are not the problem, I swapped them and both SE's still show the same problems.

Swapping the roms was one of the things I've tried, I found out that sometimes, the roms in a ceramic package loose their content. (I've spent ages troubleshooting an IBM XT Clone only to find this out...)

UE8 is a new part, it is a SN74LS166AD from TI, I bought it here
Posted by: Ferrix97 on 2015-07-31 13:12:24
I found out that the interrupt key produces a sad mac chime only if you press it after the startup chime, if you wait more that 6-10 seconds it does nothing

on the other hand, the reset button always works

I tried the same thing with the other board (the one with half video) and no matter when you press it (with no drives hooked up), it always makes a sad mac chime (that ends with 13, if I remember correctly)
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