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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: huronking on March 24, 2016, 02:01:17 PM

Title: Yet another A3000 SCSI thread.
Post by: huronking on March 24, 2016, 02:01:17 PM: I swear I thought my main A3000 battery had already been replaced with a 2032 socket.

It wasn't, and it is screwed. It runs but the flickering video says it won't for long.

So I dig in the closet and swap out the motherboard with a ill-conceived 15-year old tower conversion project that has been gathering dust. It had the 2032, but it had long since died.

I pieced it together, and it will not recognize the SCSI drive. I ran SETBATT and it confirmed the power loss, but looks ok otherwise. The jumpers are identical, and both boards are missing the terminators. If that worked on one why not the other?

I put an A2091 in a slot and connected the same drive. It booted up fine.

I know SCSI is fickle, especially when it comes to termination, but why would a configuration work on one A3000 but not the other? What am I missing?
Title: Re: Yet another A3000 SCSI thread.
Post by: Oldsmobile_Mike on March 24, 2016, 02:38:04 PM: Different version of the WD chip?
Title: Re: Yet another A3000 SCSI thread.
Post by: matt3k on March 24, 2016, 04:05:07 PM: For yucks try terminating the motherboard and see.

Swap the chips and see.
Title: Re: Yet another A3000 SCSI thread.
Post by: huronking on March 24, 2016, 04:47:06 PM: I did swap the WD chips although they are the same revision and it didn't change the behavior. As far as terminating the motherboard I'd have to order the terminators. I have three A3000's and none of them have them.

I assume that a DB25 terminator on the back would do, they are readily available online.
Title: Re: Yet another A3000 SCSI thread.
Post by: kneehighspy on March 24, 2016, 08:03:16 PM: i would guess the terminating resistors also on the motherboard, had pretty much same issues and replacing the resistor packs worked. both the internal 50 pin and external db25 work fine on my a3000.

//kneehighspy
Title: Re: Yet another A3000 SCSI thread.
Post by: r.cade on March 25, 2016, 01:14:47 AM: There is a diode that gets blown on a lot of A3000's when plugging/unplugging powered external devices. Test/replace it and see if that's it.
Title: Re: Yet another A3000 SCSI thread.
Post by: mechy on March 25, 2016, 04:50:29 AM: Quote from: r.cade;806323
There is a diode that gets blown on a lot of A3000's when plugging/unplugging powered external devices. Test/replace it and see if that's it.

also check the diode is good and not shorted. It was installed backward on some a3000 revisions. termination wont work without this diode that supplies +5v term power.

@Huron : A3000 scsi is not fickle, all the problems are known and fixable. In the 20 years i have been messing with Amigas i have proven this to many people who swore they had to do a ritual to sacrafice a chicken and dance on 1 foot while touching the scsi cable to make it work :)
:roflmao:
Title: Re: Yet another A3000 SCSI thread.
Post by: huronking on March 25, 2016, 05:01:42 AM: Quote from: r.cade;806323
There is a diode that gets blown on a lot of A3000's when plugging/unplugging powered external devices. Test/replace it and see if that's it.

It tests exactly the same as the original motherboard including polarity.

It's crazy.
Title: Re: Yet another A3000 SCSI thread.
Post by: r.cade on March 25, 2016, 12:16:16 PM: Ah, well then you'll need to start checking for broken traces and start testing the other TTL support chips related to SCSI. Sounds like no easy fixes...

Also, I agree- The A3000 SCSI is very robust, even with the "proto" WD chip.
Title: Re: Yet another A3000 SCSI thread.
Post by: huronking on April 09, 2016, 11:12:03 PM: I ordered an external terminator... It misbehaves differently but still does not work. I guess it doesn't matter since the A2091 works just fine in it. Just seems a little bit of a waste.