Dragon 32 with DRAM removed, video output?

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wayland
Posts: 39
Joined: Mon Nov 28, 2022 6:28 pm

Re: Dragon 32 with DRAM removed, video output?

Post by wayland »

Yeah, I replaced all the fuses with 3 amp. If something is blowing fuses then that part is already broken and will need to be replaced. I have removed the last tant on the -5v line but that line still shorts the PSU.
I'm suspecting the op-amp.
dublevay
Posts: 173
Joined: Wed Jan 23, 2019 3:41 pm

Re: Dragon 32 with DRAM removed, video output?

Post by dublevay »

That's really not advisable. As per the warning notices, some of these fuses are for fire protection, whilst the lower rated ones are designed to protect you equipment. I would strongly advise to return to the original values, and just use the 125mA for F3 if necessary.
dublevay
Posts: 173
Joined: Wed Jan 23, 2019 3:41 pm

Re: Dragon 32 with DRAM removed, video output?

Post by dublevay »

I've just noticed what's wrong Wayland - at least, this is one definite fault.

Please check the instructions for the required and optional header populations - sections 2.6.1 and 2.6.2. JP2 is mandatory. You need to fit JP2 and connect the middle and right pins for composite signal.

CN11 is optional. For CN11 you have a jumper across the composite signal and ground - which is killing your composite signal. That is a output connector, not a jumper selector. It's for pulling the composite and sound out to another device. Remove that jumper and fix JP2 and your composite output should work.
wayland
Posts: 39
Joined: Mon Nov 28, 2022 6:28 pm

Re: Dragon 32 with DRAM removed, video output?

Post by wayland »

I needed the stronger fuses so the dodgy components would fry. Mainly tants. I will set it back to the correct fuses once I have removed all the shorting components. I don't leave it unattended in this state.

So I need JP2 to get an output? I will give that a go.

I have sort of moved on because I bought another Dragon 32 which is complete and works. CoCoSDC will allow me to load programs.

I am now sourcing the parts to fit a Raspberry PI running XRoar to the old case. I can retain the Dragon keyboard because I can use a Pico to turn it into a USB Keyboard. It will be a bit weird having a Dragon 32 running Linux then have it launch into XRoar.
prime
Posts: 266
Joined: Fri Apr 10, 2009 1:40 am

Re: Dragon 32 with DRAM removed, video output?

Post by prime »

wayland wrote: Sun Feb 19, 2023 11:11 am Yeah, I replaced all the fuses with 3 amp.
Caution from the PSU board designer......

3A is probably ok on the 5V and 12V lines (the 12V is just passed through anyway), and the 5V reg is rated at 3A, though it will get hot, if you draw 3A from it!

However the -5V/-12V circuit is only good for 750mA, so with a 3A fuse you risk damage / fire if something goes wrong in the -ve voltage circuit.
Please replace it with a lower rating, 500mA should be fine.

Likewise nothing should be drawing large currents from the monitor port so the fuse in that circuit should be a low value 200mA max. It's really only there to provide a voltage for auto-switching SCART.

Cheers.

Phill.
wayland
Posts: 39
Joined: Mon Nov 28, 2022 6:28 pm

Re: Dragon 32 with DRAM removed, video output?

Post by wayland »

It will only be a very tiny fire :lol:
It's for debugging purposes.
I have about 15 laptop PSUs, it would have been really good if the 12v line had a buck converter too then it would handle 19v. That's the biggest risk that I see, that someone will plug in a laptop PSU and ruin a good Dragon.
I've got to re-visit this and put the video link in so I get some output.
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