TF328 RGB weird signal on amiga CD32

[leeuwtje]

Hi guys,


I have a bit of trouble here, and the worst part, I did to myself.

Amiga CD32 + TF328 card.
The amiga Cd32 was recapped 3 years ago. It worked fine with the terrible fire and CF CArd till yesterday for years.
All this time I used the original black brick psu on it which worked good.

Today I took an Amiga 500 psu which i modified a few years earlier with a CD32 power connector plug, to use it on cd32.I wanted to see it still works ok (it worked good some years ago.) So today I took a universal meter to check the voltages on it, it said 5 and 11.85 volt, so I assumed I could try it on the CD32.

If it is coincidence, I don't know, but after trying that I lost the RGB signal on the Tf328 card. The intro sound was working tough, but a weird image on screen. Quickly I reconnected the orginal brick psu back to see if that fixed the problem but no...
First I thought I killed my cd32, but luckily that is not the case. When I connected the CD32 with composite (yellow, red,white) i had vision again on screen. Also the workbench started on the expansion card CF, so in fact the tf328 is working... The LED's and Keyboard light were on. And the sound worked as well.
So...i hope it is not so terrible as I was afraid for, like blowing up my mate, the CD32.

My question, does anyone has weird experiences with the RGB video signal on these cards? i tried 2 different tv's (monitors), a CRT gives nothing, another LCD screen gives a weird waving screen, like an old tv tuner not tuned right on the tv channel. (If that makes sense to anyone)

Stupid. wish, I left it alone. Or, is there something coincidental going on? Unfortunately I have no spare Amiga RGB Scart cable lying around here, to test that part out.

[supaduper]

Check those RGB to Scart cables guys, I blew a Alice chip on my CD32 because of poorly made cables, what happens is they are a loose fit in the hood and movement can disconnect the wire solder joints on the internal pins and short out, and you just cant see it happen, I now open every one bought and check the joints and re wrap the cable where it enters the hood so there is no movement so the cable is held snugly.
see before and after pic below

[MiaM]

If the orgiginal CD32 power supply has an ungrounded mains plug then you could have damaged something due to a ground loop (either if the monitor is grounded through a completely different wall socket than the one you used for your A500 PSU, or if there is loads of leaks in the mains finter in the monitor (common on the Philips made 108x/88xx monitors) and you plugged in or out the RGB wire while the power supply were connected (even if it was off).

Not sure how the TF328 works, but if it uses +12V for the RGB output then you could have a broken power switch on your CD32. Check if it can read CDs. If not then check if 12V passes through the switch.

Afaik it's for the switch to NOT break. (On my CD32 the switch lasted for only a few flicks the same day as I bought my CD32 at a flea market in the late 90's. Permamently added solder blobs as a sort of lobotomy on the switch).

[leeuwtje]

Guys, thanks for all the idea's here. Supaduper's help inspired me to start with logical steps, and open up the RGB scart cable. Then it became obvious Pin 16 has come loose which supports the ground of the RGB color signals according to an electrical scheme I found on the net. I should have checked it before opening a ticket. Logically this explains the reason, but not the coincidence when I was just trying another psu. I probably moved the video cable too much in the movement.
Since the quality of the soldering of the other pins in the RGB connector were everything but good, i decided to order another cable.

Thanks supaduper and Miam.

Miam; Can my stock CD32 psu handle the extra load from the expansion card in Current? Would there be a problem?
About the ungrounded plug; No the cd32 psu has no grounding, not in the wire at least.
I read about a procedure to restore an Amiga 500 psu by taking the original board out, and use the shell and wires to mount a modern psu board. There is a youtube movie for it. It is not crazy expensive and it would give a warranty for a healthy amiga and a grounded psu. Or would a recap be better? Are these heavy mods really necessary in 2021 or can just use the Amiga 500 brick as it is? I use the Amiga 500 psu as a backup for the CD32 now.