exxos's Atari, Amiga & retro forum

Well, it worked for a bit and then when connected to the OSSC it caused the Memotech to crash after garbling the display and now seems to short out the RGB2HDMI. All the wiring is correct.

No idea what's happened.

With the cable disconnected from either of the two converters then the machine boots OK, so it's the TMS-RGB board which is having issues.

Yep. The TMS-RGB is having issues. This is NOT what the blue video output should look like!



25V peak-to-peak!!!!!!

I'm pretty sure it's killed the RGB2HDMI and may have done damage to the OSSC.

The other outputs (R, G & composite sync) are all ~2V peak-to-peak and have the correct signals.

stephen_usher wrote: 08 Oct 2022 18:21
25V peak-to-peak!!!!!!

I'm pretty sure it's killed the RGB2HDMI and may have done damage to the OSSC.

Holy hell, where did 25v p2p come from? I really hope your RGB2HDMI and OSSC are ok.

Yikes! :shock: :?

rubber_jonnie wrote: 08 Oct 2022 18:29

stephen_usher wrote: 08 Oct 2022 18:21
25V peak-to-peak!!!!!!

I'm pretty sure it's killed the RGB2HDMI and may have done damage to the OSSC.

Holy hell, where did 25v p2p come from? I really hope your RGB2HDMI and OSSC are ok.

I have no idea, given that the board is only supplied with +5V! The only other connections are the component outputs, RAS for the video RAM and one data line to the video RAM.

stephen_usher wrote: 08 Oct 2022 18:40

rubber_jonnie wrote: 08 Oct 2022 18:29

Holy hell, where did 25v p2p come from? I really hope your RGB2HDMI and OSSC are ok.

I have no idea, given that the board is only supplied with +5V! The only other connections are the component outputs, RAS for the video RAM and one data line to the video RAM.

Not good, hope you can figure it out.

The moral of the story is... beware how you route your cables!


I'd let the ribbon cable rest over the top of the legs of components coming through the board. Unfortunately, just at this point there's a pad on the lower case which, when the bolt to secure the motherboard and give thermal transfer from the heatsink was tightened it compressed the motherboard onto the cable and the lead from one of the diodes connected to the 16V A/C input from the transformer punched through the insulation and into the blue lead. If it had been 0.5 millimetres further over it would have hit the GND and there would have been a connection between ground and 16V A/C, which would not have been pretty.

As it is I seem to have got away with a damaged ADC daughter board on the RGB2HDMI (I hope that it's just the daughterboard).

The output from the TMS-RGB seems to have vertical banding that I didn't notice before but it otherwise works with the OSSC.

Looks like it's just the ADC board. Let's see if I can find a replacement!

I once had a piece of wire impaled like that to the bottom of an ST mainboard. Caused chaos and being green it was very hard to see. Luckily there were no serious voltages involved.

Hope you can fix your stuff easily (And cheaply!!)

I’ve ordered another add board for the RGB2HDMI, £35 quid via SellMyRetro.