A3000 SCSI boot problems

[ffffr0zen]

Hey, I accidentally fried my SCSI controller chip by using a SCSI Zip drive with my A3000. I just replaced the chip and the A3000 is finally booting from floppy again but can't get it to boot off a hard drive.

At first I was getting a solid green HD light and a white screen at boot. The hard disk wouldn't even spin up. Now I just get a white screen with no HD light.

Anyone come across this problem before or know a possible solution? I've googled and bing'd but couldn't find any help.

The hard disk spins up when the SCSI cable is disconnected. I've tested the HD on another computer, it was ok, and tested the A3000 with a seperate drive, same issue.

The new SCSI chip I got is the AMD one. I'm hesitant to plug the Zip drive back in for a test, but can't think of anything else to do.

Cheers in advance!

[patrik]

Does the A3000 boot from floppy with the harddrive connected? If so, what happens if you try running hdtoolbox from the install disk?

Btw, how comes the zip drive burned the scsi chip? Is it not a scsi zip, but a parallel-port zip?

[Hedeon]

There are internal SCSI zip drives.

[idrougge]

Originally Posted by Hedeon

There are internal SCSI zip drives.

[Hedeon]

Dunno what it is, lately. I was convinced I read something about that scsi zip was a myth and that it really was a parallel port zip.

I need new glasses.

[nexus]

apple used internal scsi zips
https://www.amazon.com/Iomega-Z100SI.../dp/B00078V7BQ

[ffffr0zen]

Hi all, thanks very much for the replies.

Sorry I wasn't getting email notifications so didn't realise anyone had replied.

It wouldn't do anything with the HD connected.

And now actually it won't boot at all... but I'd still like to fix the original problem which is the continuous HD light at boot with a SCSI HD connected.

I'm not sure why the SCSI Zip drive fried the controller chip but I think it has something to do with the way external Zip drives terminate (or don't) the SCSI bus.

The other option is that both my SCSI HDs are toasted as well as far as the A3000 is concerned, if I can get it to boot again I will test another drive.

[shaf]

what revision board is the A3000 there was a fix for the external SCSI connector or the 1N4148 Diode at D800 might be blown.

[ffffr0zen]

Hi shaf, thanks for your message.

The A3000 is booting again from disk but still light on for HD and hanging on a white screen, have tested 3 seperate SCSI internal HDs.

The SCSI controller chip I installed is the AM33C93A-16PC DIP-40. Don't know if that's maybe causing an issue with the ROMs 2.04.

Still haven't tested the external Zip drive, but apparently the AMD chip is more compatible with them.

The board revision is Commodore B2, FAB 313312 REV 9/03, P/N 313313 REV 9/03.

Edit: Just checked D800 with a continuity meter, it allows current in both directions. Also the black line is facing away from the mobo, I read elsewhere that it should be facing the mobo? Does that Diode affect internal SCSI or just external?

Here's the post discussing D800's black band:
http://eab.abime.net/showpost.php?p=957842&postcount=4

[grelbfarlk]

I used a SCSI External ZIP drive for a long time with various HDD controllers, GVP, DKB etc. Still have it actually and recovered some stuff off of them a couple years back.

[ffffr0zen]

My Zip drive worked fine for a while too until I ejected a Zip disk while it was connected.

Found this info about D800:

http://amiga.serveftp.net/A3000_Hard...termpower.html

[patrik]

Originally Posted by ffffr0zen

Edit: Just checked D800 with a continuity meter, it allows current in both directions. Also the black line is facing away from the mobo, I read elsewhere that it should be facing the mobo? Does that Diode affect internal SCSI or just external?

Through D800 SCSI termination power is supplied to both the internal and external connector. This is required for both passive and active termination to function and has to be supplied by at least some unit.

It is used as a protection to not allow SCSI devices to feed their termination power into the A3000 if they are powered, like an external unit with its own power supply.

One side of the D800 is connected to the TERMPWR pins (pin 25 on external, pin 26 on internal) and the other to +5V and the ring should be against the pin connected to the SCSI connectors as per above protection description.

I would recommend measuring this to be sure if it differs between revisions, but if the diode damaged as yours, that is not possible unless you cut a leg. On my rev 6.1 A3000, the ring should be against the SCSI connector.

My diode was also damaged like yours and also the PCB trace on the underside of the motherboard connecting it to the TERMPWR pins was burnt off.
http://megaburken.net/~patrik/A3000/TERMPWR-fail.jpg

[ffffr0zen]

Hi Patrik, thanks for your very helpful answer.

Here’s a picture of the diode:



Can anyone tell me if that image is the correct orientation?

I’ve read twice that the black ring should face the mobo, mine currently faces away?

Guess I will desolder it and replace it.

Edit: just got some replacement diodes 1N4148 as per the earlier post.

But looks like a royal PITA to get the mobo up. All of the connectors on the back have two hex headed screws on the back and my adjustable spanner is too clunky.

Any precautions I should specifically take?

Could I just clip the old diode off and solder the new one on the top side for testing?

[Jope]

This is the correct direction. According to the document, you should just measure between the stripe side + pin 25 of the external scsi port.

[ffffr0zen]

Kiitos paljon Jope

Ok, just clipped the diode, actually the middle of it just broke off without much effort.

I tested continuity from each side of the diode connectors to pin 25 of the external SCSI connector and was assuming the side of the diode that had the black band would connect to pin 25 but it was the opposite. The pin facing the mobo connected to pin 25 of the external SCSI. So seems the diode was originally installed back to front.

Can anyone confirm my testing is accurate?

So I'm assuming now I should add a new diode in the opposite direction with the black band pointing right relative to my previous photo, as in towards the mobo?

EDIT: additional question, why was my A3000 working before with a backwards diode, and why did it stop working when the diode failed?

BTW, I've got some alligator clips, can I just clip the diode on to test if it works in the opposite direction? Tried, not sure I can get the power supply back on...

[patrik]

Originally Posted by ffffr0zen

I tested continuity from each side of the diode connectors to pin 25 of the external SCSI connector and was assuming the side of the diode that had the black band would connect to pin 25 but it was the opposite. The pin facing the mobo connected to pin 25 of the external SCSI. So seems the diode was originally installed back to front.

Can anyone confirm my testing is accurate?

Yes, the diode should stop termination power from being fed backwards from SCSI devices into the A3000, so the ring should be on the side connected to the external connector on pin 25 and internal connector on pin 26.

Originally Posted by ffffr0zen

So I'm assuming now I should add a new diode in the opposite direction with the black band pointing right relative to my previous photo, as in towards the mobo?

Sounds correct given your measurements.

Originally Posted by ffffr0zen

EDIT: additional question, why was my A3000 working before with a backwards diode, and why did it stop working when the diode failed?

BTW, I've got some alligator clips, can I just clip the diode on to test if it works in the opposite direction? Tried, not sure I can get the power supply back on...

Maybe the diode has nothing to do with this failure.

Maybe your termination is working perfectly because it gets power already.

More regarding the diodes task to provide termination power:

SCSI terminators need TERMPWR. How they get the power is not straight-forward however.

The simplest case is a separate terminator which can only be powered from the TERMPWR line on the SCSI bus.

It gets much more complex on an harddrive with onboard termination. For example an old 2GB Seagate I have can be jumpered to source termination power from the drive or the bus. Additionally, it can be jumpered whether or not it supplies termination power to the bus. Other drives may not be configurable and might always supply power to its onboard terminators and or the bus.

The motherboard termination in the A3000 is supplied by 5V directly according to the schematics, so it should work disregarding. However, it should not be used if using the external port, as then you would terminate the middle of the chain.

[r.cade]

I highly doubt that linked article about the diode being installed backwards or the board silkscreened wrong is correct, but who knows.

The diode keeps EXTERNAL devices from putting 5V INTO the board, not restricting the 5V TO external devices.

When this diode blows short, what happens is that external devices will be able to power the A3000 motherboard even when it's off, as well as cause all sorts of other problems. It's designed to protect the A3000 motherboard and power supply, not external devices.

[ffffr0zen]

So just soldered in a new diode on the top side to the stems of the old one.

In the opposite direction.

Tested it with a continuity meter and can confirm that it does not allow current to go from pin 25 of the external SCSI port to the mobo, but does allow current from the mobo to pin 25.

However after booting up I still get the solid HDD light and a white screen, but boots to floppy without HDD connected.

Will probably have to inspect the underside of the mobo. Unless anyone has any other suggestions?

What else could possibly have fried if the external SCSI Zip drive wasn't terminated properly?

Do I need to test the diode in the original direction just to be sure?

Where do I find out if there are terminator resistor packs installed on the mobo? I noticed there are some pin headers just above the 50pin internal SCSI connector on the mobo.

[r.cade]

Sorry, I don't think anymore meant to tell you that would fix your problem - the diode won't stop anything from working, especially if you aren't using external SCSI.

I would check the board top and bottom to make sure traces aren't burned, though.

[ffffr0zen]

Did some further testing...

Attached the external SCSI Zip, with an internal SCSI HDD -> White screen hang but no HDD light

Attached the external SCSI Zip (With disk in) -> Boots to ROM screen/insert disk

Attached an internal SCSI CD-ROM drive, with no disc -> Boots to ROM screen/insert disk

Anyone know off hand of a bootable CD-ROM image with workbench or anything? Can you boot an A3000 from CD-ROM? And can I burn it using a PC?

EDIT: Found this thread with a bootable CD rom image:

http://eab.abime.net/showthread.php?t=67898&page=2

Apparently works on an A3000... however on mine it did not boot. Its a CD rom drive from a dead Mac LC575, never tested it on my A3000 before so not sure if it's compatible. The disc did make some seeking noise when inserted but just went to insert disk screen.

Disconnected the CD-ROM. Reconnected my main SCSI HDD.

New symptoms now. The A3000 will boot to insert disk screen with the internal SCSI HDD attached. No constant HDD light. But the SCSI HDD is not spinning up at boot. A change from white screen and constant HDD light at boot.

I noticed the CD-ROM drive had a termination jumper set to on, maybe it cleared some flags or something?