What's going on with this 3000T?

[Matt_H]

Anyone ever seen this before? The 4.7K resistor at R203 has been clipped off and the NTSC/PAL selector is jumpered not with a standard jumper block, but with another resistor (unknown type - might not even be a resistor) soldered directly to the pins.

Any reason for this? If not, I'll be putting it back to normal when I put a new battery in.

EDIT: An additional detail, this is on an "official" 3000T-040 - the kind with a 3640 bolted to the motherboard and no 030 or 882 chips.

[Oli_hd]

Maybe the last owner wanted a NTSC/PAL switch mounted somewhere and was going to use the case as the return (ground) so he put a resistor between the signal and vcc (positive), ran one wire to the switch (saving a second wire)

Sounds silly I know but its about the only reason I can think of.

[Zac67]

Got no schematics for an A3kT, but on a D R203 is the pullup for the _NTSC/PAL/TEST pin - quite unnecessary since Agnus has got an internal pullup. The jumper has one contact to said _NTSC/PAL pin, the other is GND, so closing it selects NTSC.

Can't see too much sense in that setup apart from saving a minute amount of energy... (5V/4700Ohm ~= 1mA, @5V that's 5mW)

I'm only speculating, but it might be a test setup for some Agnus variant that ran some other signal on that pin. Rather than burning that signal down with a GND short, the resistor limits the current and therefore saves the driver from being killed. The R203 pullup would work against the weak pulldown, so it was removed.

[Matt_H]

@ Zac67

Interesting... with that explanation, the two mods sound to be definitely related. I've got 3000T schematics, so I'll check those.

[oldman3000]

I think it has something to do with the PPC board if you ever installed one. I don't know why it's cut, but my A3000T was cut also, I look at the electric drawings today.

Mike
San Diego

[Matt_H]

oldman3000 wrote:
I think it has something to do with the PPC board if you ever installed one. I don't know why it's cut, but my A3000T was cut also, I look at the electric drawings today.

Mike
San Diego
I never had a PPC in it, but maybe a previous owner did. I think it was an ex-video system, though (came with a TBC and PAR), so a PPC in its past is unlikely.

@ Zac67

I've looked at the 3000T schematics and it seems like the thing on the NTSC/PAL selector might be serving as the replacement for the removed jumper.



Some unrelated 3000T trivia that I learned while working:
~The FCC ID is BR9A3500, a vestige of the early name for the model.
~One of the other 3000Ts I have has serial number 67.

[oldman3000]

If the battery had been replace about 4 to 10 years ago, a repair man would have cut it for add-on boards. I know at that time I thought all Amiga's were going to be PPC. I know that on some of the Amiga, the ECS ones there was a conflict on the motherboard.

Mike
San Diego

[Matt_H]

oldman3000 wrote:
If the battery had been replace about 4 to 10 years ago, a repair man would have cut it for add-on boards. I know at that time I thought all Amiga's were going to be PPC. I know that on some of the Amiga, the ECS ones there was a conflict on the motherboard.

Mike
San Diego

I removed the battery myself a few years ago. I hadn't noticed the clipped resistor at that time. As to a conflict, are you sure you're not thinking of the INT_2 mod?

[Zac67]

Matt_H wrote:

~One of the other 3000Ts I have has serial number 67.
That one obviously belongs to me. :lol: *SCNR*

[Matt_H]

Zac67 wrote:
Matt_H wrote:

~One of the other 3000Ts I have has serial number 67.
That one obviously belongs to me. :lol: *SCNR*
:-D

Unfortunately, it's also not working correctly. I'm 1 for 3 on operational 3000Ts, and the one that is working is in awful cosmetic shape.

Arrg! Frustrating!

[oldman3000]

I guess I was wrong, but like the serial number. I'm 175. What are the other numbers out there. I don't think there was a lot of A3000T.

Mike
San Diego

[gdanko]

EDIT: An additional detail, this is on an "official" 3000T-040 - the kind with a 3640 bolted to the motherboard and no 030 or 882 chips.

What makes the 3640-enabled 3000T official and the 030 flavor not?

[Matt_H]

gdanko wrote:

EDIT: An additional detail, this is on an "official" 3000T-040 - the kind with a 3640 bolted to the motherboard and no 030 or 882 chips.

What makes the 3640-enabled 3000T official and the 030 flavor not?
I think you misunderstood. What I meant by official was that this machine has a factory-installed 3640 and is stamped with "3000T-040" on the case, as opposed to being a regular 3000T that someone later put a 3640 board into.

I mentioned it because I thought the motherboard changes might have also been part of that designation.

[gdanko]

That makes sense. I have the latter..it's got an 030 chip. :) But hey, 3000Ts are hard to come by so who's complaining?:) When I got it, it had a CSPPC in it.. *drool*

[T3000]

My A3000T/040 is serial # CA1000927
There is second label indicating A3000T-040
the '030 and 882 chips are present.
The resistor at R203 is not present and apears to have been clipped.
NTSC/PAL jumper is of normal type.

[Matt_H]

@ T3000

That's interesting. Are you the first owner of that machine?

[T3000]

Matt_H wrote:
Are you the first owner of that machine?

No. Though I did by it from the original owner some time in the late 90's. He had installed an AD156 audio card, a 500 meg system HD, two 2gig HDs set up for audio, some tape drive for backups and used it in his profesional recording studio. Other than that it was stock with a 40mhz A3640/16fast/2chip. Paid around $800 at the time with a monitor, software and manuals.

Since I aquired it I had installed a VT/PAR/TBCIV/FLZIII w64 ram, 4 gig system HD, 4 gig audio HD, two 4 gig PAR HDs and an external 100meg ZIP along with the Ad516 and Tape drive. Aquired the latest chip upgrade and was eager to install them to get the FLZIII scsi to function.

System was working fine untill one day I turned it on to work on a project. Nothing but a green screen...
Currently striped down and attempting to "fix" it. Reset all the chips, replaced the Agnus and A3640. Tested and replaced the power supply. Think I toasted the high density floppy drive working on it late the other night...

[Matt_H]

@ T3000

What revision 3640 was/is in it? Mine's a rev. 3.0 and the motherboard has stock 2.04 ROMs. I'm wondering if the resistor changes might be some sort of workaround for the bugs in the 3.0 board revision.

[T3000]

Matt_H wrote:
What revision 3640 was/is in it? Mine's a rev. 3.0 and the motherboard has stock 2.04 ROMs. I'm wondering if the resistor changes might be some sort of workaround for the bugs in the 3.0 board revision.

3.1 3640 with 2.04 roms
upgraded the roms to 3.1