archive.worldofdragon.org

Can someone clue me in as to why the MKII power board with the UM1233 modulator is classed as obsolete and should be replaced by a MKI or MKIII power board.
I picked up another D32 off feeBay and it arrived today, at first I thought it was banjaxed but it was just the C11 tantalum capacitor going pop, it worked okay even with it broken. I replaced that and checked the voltages from the board and were all good. Did the service mods recommended for 16 x 16 and seems happy enough.
Just wondering if there is a flaw in MKII power boards that makes them very dangerous for prolonged use…
The actual PCB says issue 6 on the top and issue 7 underneath. I based all this on the modulator to determine it’s a MKII unless they used UM1233’s again later on.

Could you tell us the part number of your power board, and possibly upload pictures from both sides?

We do have pictures of several power boards here, but none as the one you describe.

robcfg wrote: ↑Fri Nov 12, 2021 7:35 am Could you tell us the part number of your power board, and possibly upload pictures from both sides?

We do have pictures of several power boards here, but none as the one you describe.

Will do that over the weekend for you.

Here are the pictures…

The power supply side of things looks like the usual circuit. I wonder if the problem with 'MKII' boards was to do with the separate audio subcarrier circuit.

I'm also wondering what a 'MKIII' looks like.

sorchard wrote: ↑Fri Nov 12, 2021 2:14 pm The power supply side of things looks like the usual circuit. I wonder if the problem with 'MKII' boards was to do with the separate audio subcarrier circuit.

I'm also wondering what a 'MKIII' looks like.

It is probably a moot point for me and most of us these days as I use the composite output these days so maybe the obsolete advice is in fact obsolete

Interesting...

The only differences I can see is that the footprint for RV1 is slightly different between Issue 6 and Issue 7 power boards, and that your Issue 7 board has the link below C17 connected.

Do you mind if I upload your pictures to the power boards page?

By the way, as far as I know there are no MKII or MKIII power boards, are the ones you are referring to actually main boards?

I think I understand now: The three board types are mentioned in the archive here

These are the various versions we know about:
- MK1 boards with a UM1286. Photos in the archive show they go up to at least issue 4
- MK2 boards with a UM1233. These have been seen up to issue 6 / 7
- MK3 boards with a UM1287. These use the earlier issue 4 boards but the resistors next to the modulator have different values compared to MK1

Ah, I see, thank you for the explanation!

There's also the Secam board with a UM1601 modulator, and the NTSC modulator from the Tano Dragons which seems not to be Astec ones, but were designed along the PSU board.

robcfg wrote: ↑Fri Nov 12, 2021 6:35 pm Interesting...

The only differences I can see is that the footprint for RV1 is slightly different between Issue 6 and Issue 7 power boards, and that your Issue 7 board has the link below C17 connected.

Do you mind if I upload your pictures to the power boards page?

By the way, as far as I know there are no MKII or MKIII power boards, are the ones you are referring to actually main boards?

No problem, feel free to use them on the archive