View Profile: nztdm - Vintage Computer Forum

Yesterday, 05:40 PM

nztdm started a thread Help diagnosing a 1084S-P Monitor in Vintage Computer Hardware

Hello! I acquired a faulty 1084S-P AU (I think AU means PAL and 230V). It worked for a short moment, displaying a wonderful image of the C64...

1 replies | 24 view(s)

February 17th, 2021, 10:08 AM

nztdm replied to a thread Help diagnose sporadic sync on IBM CGA card's composite output in Vintage Computer Hardware

I seee. After playing with those pots, I noticed the CGA card old/new type identifier image showed it now had roughly the new-type colours, so...

26 replies | 373 view(s)

February 16th, 2021, 06:16 PM

nztdm replied to a thread Help diagnose sporadic sync on IBM CGA card's composite output in Vintage Computer Hardware

Ahh yep, thanks. It appears the new-type cards have a pulldown, and wildly different resistor values. The new-type produces different colours...

26 replies | 373 view(s)

February 16th, 2021, 03:57 PM

nztdm replied to a thread Help diagnose sporadic sync on IBM CGA card's composite output in Vintage Computer Hardware

Please see my previous replies. Did you see the schematic? It doesn't have pullup or pulldown like the new-type CGA. To add on to my previous...

26 replies | 373 view(s)

February 16th, 2021, 03:26 PM

nztdm replied to a thread Help diagnose sporadic sync on IBM CGA card's composite output in Vintage Computer Hardware

I added a 10k trimpot as base pullup. When turned up to 10k, it syncs but the image is bright and washed out. Turning it down until the background...

26 replies | 373 view(s)

February 16th, 2021, 03:05 PM

nztdm replied to a thread Help diagnose sporadic sync on IBM CGA card's composite output in Vintage Computer Hardware

Shorting out R17, makes it sync perfectly, but it's a bit too bright and washed out (too high luma level?). Perhaps the composite output from the...

26 replies | 373 view(s)

February 16th, 2021, 02:51 PM

nztdm replied to a thread Help diagnose sporadic sync on IBM CGA card's composite output in Vintage Computer Hardware

Neither of my displays detect a signal when chroma is missing (likewise, they won't sync to a Commodore 64 with only the luma plug connected). I was...

26 replies | 373 view(s)

February 16th, 2021, 01:41 PM

nztdm replied to a thread Help diagnose sporadic sync on IBM CGA card's composite output in Vintage Computer Hardware

Yes it's always perfect on the digital output with a 5153. Used it like that for about 2 years. I never actually tried the composite output of the...

26 replies | 373 view(s)

February 16th, 2021, 02:06 AM

nztdm replied to a thread Help diagnose sporadic sync on IBM CGA card's composite output in Vintage Computer Hardware

I've taken some more scope readings. Here is a link to the high-res image. And a lot more videos which may be helpful in my Twitter thread.

26 replies | 373 view(s)

February 15th, 2021, 12:21 AM

nztdm replied to a thread Help diagnose sporadic sync on IBM CGA card's composite output in Vintage Computer Hardware

My composite GND has been running through mains earth. I can see the inner layer connection to the RCA jack's sleeve, but there is no connection to...

26 replies | 373 view(s)

February 14th, 2021, 11:48 PM

nztdm replied to a thread Help diagnose sporadic sync on IBM CGA card's composite output in Vintage Computer Hardware

If I connect a wire here (U67 GND to composite GND), the undershoots are reduced and the sporadicity of the sync issue is reduced. Text-mode shakes...

26 replies | 373 view(s)

February 14th, 2021, 11:14 PM

nztdm replied to a thread Help diagnose sporadic sync on IBM CGA card's composite output in Vintage Computer Hardware

I assume R5 is what connects chroma. I lifted a leg of that, and the undershoot below 0V is still there. I don't see any undershoots on the...

26 replies | 373 view(s)

February 14th, 2021, 09:50 PM

nztdm replied to a thread Help diagnose sporadic sync on IBM CGA card's composite output in Vintage Computer Hardware

Maybe I'll give the board a good wash if I can't find anything else. Is tin whiskers a common thing with leaded solder?

26 replies | 373 view(s)