Thread

Macintosh SE/30 Faint chime and no video, possible short on +5V

68kMLA Troubleshooting 28 posts Jul 24, 2015 to Jun 28, 2022

#1 Fri, 24 Jul 2015 - 16:42 68kMLA

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

#2 Fri, 24 Jul 2015 - 17:26 68kMLA

Likely both bad caps and damaged traces. The UE8 section looks more than a little gunky.

#3 Fri, 24 Jul 2015 - 17:46 68kMLA

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.

#4 Fri, 24 Jul 2015 - 18:41 68kMLA

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

#5 Fri, 24 Jul 2015 - 18:52 68kMLA

sounds like might be a bad floppy bourns filter, or bad scsi chip.. or bad lines to the scsi i/c.

#6 Fri, 24 Jul 2015 - 19:22 68kMLA

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?

#7 Fri, 24 Jul 2015 - 20:17 68kMLA

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.

#8 Fri, 24 Jul 2015 - 20:20 68kMLA

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?

#9 Fri, 24 Jul 2015 - 20:25 68kMLA

I set my hot air station at 575F

flux and tweezers? - not sure if that was your question.

#10 Fri, 24 Jul 2015 - 20:30 68kMLA

perfect!, thanks!

does the system start up if I only supply +5V using my bench power supply?

#11 Fri, 24 Jul 2015 - 20:35 68kMLA

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

#12 Fri, 24 Jul 2015 - 20:51 68kMLA

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

#13 Fri, 24 Jul 2015 - 21:03 68kMLA

It doesn't need -12v to boot but it does power the sound amplifier setup so you would get any internal sound...

#14 Fri, 24 Jul 2015 - 22:48 68kMLA

the low ohms on 5V is actually normal, its the combination of the CPU and PALS loading down the 5V supply.

#15 Fri, 31 Jul 2015 - 16:31 68kMLA

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.

#16 Fri, 31 Jul 2015 - 20:02 68kMLA

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.

#17 Fri, 31 Jul 2015 - 20:09 68kMLA

also swap your video rom with the other board just for giggles.

#18 Fri, 31 Jul 2015 - 20:18 68kMLA

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

#19 Fri, 31 Jul 2015 - 21:12 68kMLA

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)

#20 Fri, 31 Jul 2015 - 22:05 68kMLA

you have a broken address/data line between the video circuit/sound, and SCC/SCSI.

Also, listen to your sound, if it sounds "funny" then thats what it is.

#21 Fri, 31 Jul 2015 - 22:11 68kMLA

The sound seems to be ok, both the startup chime and the sad mac tone are loud and clear. Only once, the sad mac tome was "slower" than usual.

#22 Fri, 31 Jul 2015 - 22:20 68kMLA

Do you have a screenshot of the issue?

Edit: does this have a completely black screen? The only time I came across a unit that was totally black even though it chimed, was bad VRAM. I have had to change out VRAM at least 3 times that I can recall.

#23 Fri, 31 Jul 2015 - 22:28 68kMLA

The screen remains all black, the analog board is good (tested with another SE and the half-video SE/30, the one in the other thread)

The "slower" tone only happened once, after rebooting the machine it came back as usual

I also replaced one of the Bourns filters, RP2 if I recall correctly (desoldering it was quite a pain) but it still doesn't boot

So, At this point I'm still stuck with black screen + no boot

#24 Fri, 31 Jul 2015 - 22:29 68kMLA

Feel around on the chips. see if the SCSI, SWIM is getting excessively hot.

the PALs and the SCC will get really warm. thats normal.

Bourns are easy to test. The end pins are grounded, and the middle pins should be high resistance. If you get low ohms to nearly a short on any other pin besides the outer pins, the Bourns is bad.

#25 Fri, 31 Jul 2015 - 22:35 68kMLA

Also note, the video circuit in the SE/30 will run all by itself regardless of what the BUS is doing... period. It will draw on the screen, the default state of the VRAM. Different brands of VRAM draw different initial patterns. Simasimac is created by only 1 type of RAM, while zebra stripes are created by a different brand of RAM. NEC vs TI. I think.

So, if you get black screen, the video circuit is bad and needs troubleshooting. in my EXPERIENCE, the #1 cause was the VRAM itself. Second to the PALs. if the PALs are bad, it will prevent the machine from booting as well, especially if its holding up the BUS which could also cause no video, as they are also used at refreshing the screen with whatever contents are in VRAM.

there 5 PALs. Find the one that is common to the video generation, and also attaches to some control lines on the main data bus. That would be where I would start.

#26 Sat, 1 Aug 2015 - 11:29 68kMLA

At this point, I think that the problem might be a bad PAL, maybe UE6 or UI6.

Unfortunately they are soldered, so they are not so easy to swap with the other board

#27 Sat, 1 Aug 2015 - 23:28 68kMLA

desoldering station time.