Amiga 2000 Only Works with Genlock Card

[commodorebob]

Hello everyone, I have recently run into an issue that is confounding me with my Amiga 2000 (rev 4.1 board). I got it off of Ebay not functioning, but after replacing a couple of bad DIP sockets it has been very stable. I have also been able to install a TF536 and use the A2091 with the V7 ROMs. Some other enhancements include the new 3.2.1 Kickstart and an install of Amiga OS 3.2.2.


Recently I got a ZZ9000 card and I wanted to install that into my Amiga, however I have had an issue ever since I bought the machine where it will not even POST without the A2300 Genlock card installed. From what I can tell it should be able to operate without that card no problem, which is causing issues since I cannot plug the ZZ9000 daughter card in.


I have tried playing with some of the Jumpers just as J300 but to no avail.
Would very much appreciate if anyone had any ideas.
I do have an oscilloscope if anyone has any suggestions on where to probe as well.

[Jope]

There may be multiple faults, but it seems like the Amiga wants to be externally clocked at all times. Perhaps start by probing all the different clocks at various points on the motherboard using your scope, starting from the oscillator can.

Focus on the Agnus first to see all the clocks are ok, then move on to the CPU and other chips.

[commodorebob]

So I can at least confirm a couple of things, I have swapped the Angus chip with the one from my A500, and that seemed to have no affect. I can also confirm that I am getting a solid 60Hz (it's an NTSC machine) signal from the TICK pin coming from the PSU.

One thing I am wondering is there are any signals coming from the Genlock card that could be making up for a lack of such signal on the main machine. I do see that there is a 28Mhz output pin on the card. I may need to probe to see is the internal 28Mhz oscillator is not functional on my machine.

[commodorebob]

Thanks for the help! The 28.6363Mhz oscillator looks to be bad. I got a hold of the rev 4 board schematics and probed up on FB101, which is a ferrite bead next to the Angus chip. This bead connects directly to the Oscillator. Instead of seeing the 28Mhz clock at 5V I just got noise.

I had no idea that the external clock from the genlock card could serve as a full stand in for the internal 28Mhz oscillator. Luckily it's one of the cheapest and easiest repairs compared to the alternatives.

[Matt_H]

So, I think the clock suggestion is more likely to be correct but there’s another thing to look into: are you connecting the the Amiga to a VGA monitor via the 23-pin RGB port with a simple straight-through adapter? Some of these adapters, i.e., the ones that do a direct pin-to-pin connection with no additional circuitry, can prevent non-AGA Amigas from booting because of something to do with genlock-related signals... I don’t remember the exact details.

I was trying to connect my 2000 to a 15KHz-capable flat panel with one of these adapters and it wouldn’t boot unless I had a genlock in the video slot. With a different adapter, e.g. the official Commodore silverbox, my recollection is that everything worked fine.

[commodorebob]

Luckily I'm good on the video cable front. I use the official Commodore cable hooked up to a Commodore 1084S. Of course if the new oscillator works then I hope to hook up a 1080P monitor via HDMI. One thing I did check to confirm is that I get no 7Mhz CPU clock when the genlock card was removed. Just found and ordered a compatible oscillator for $5, so hopefully in about a week I'll see if that fixes it for sure.

[Matt_H]

Alright, fingers crossed for the clock crystal! Let us know how it goes.

[commodorebob]

Good news! I after replacing the oscillator everything just worked! Now I just need to upgrade the firmware on my TF536 to fix the compatibility issues with the ZZ9000 and I'll be good to go.