View Profile: nztdm - Vintage Computer Forum

Yesterday, 02:18 PM

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

Here's the waveform across C468:

19 replies | 183 view(s)

Yesterday, 02:07 PM

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

Just took some startup measurements of PSU voltages and currents, using a current probe. Yes TS117's B is 2.5V more negative than E. I have...

19 replies | 183 view(s)

Yesterday, 01:01 PM

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

If not overcurrent on 125V, what circuit could draw excessive current only when the HOT is present? Looks like it could be anything. Not sure if...

19 replies | 183 view(s)

Yesterday, 02:40 AM

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

Unfortunately I don't have a supply capable of 125V. I have a variac, and could use that with diodes and a cap, but there would be some ripple and...

19 replies | 183 view(s)

Yesterday, 12:43 AM

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

If you think it could provide clues, I could disconnect +125V from the monitor, and connect that to a programmable load, and find the point that it...

19 replies | 183 view(s)

February 27th, 2021, 10:11 PM

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

No effect. If the SCR was triggered, the 125V output would be near-zero wouldn't it? Maybe it's related to the voltage-setting circuit that...

19 replies | 183 view(s)

February 27th, 2021, 07:55 PM

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

PSU connector M2: 1: 60V (125V) 2: 12.6V (26V) 3: 7.5V (16V) 4: GND So all voltages are a bit under half. And reducing +125V current from...

19 replies | 183 view(s)

February 27th, 2021, 07:21 PM

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

I don't have a high voltage probe so I can't check if EHT is correct level. I can only hear a correct-sounding 15kHz, and there is a good pop when I...

19 replies | 183 view(s)

February 27th, 2021, 06:57 PM

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

Putting an ammeter in series with D484 shows 24mA. (edit: so I don't imagine R484 or D484 would be getting hot) 4.0V at E of TS474

19 replies | 183 view(s)

February 27th, 2021, 05:15 PM

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

I removed C467, C468, C470, and tested capacitance with DMM, and leakage at 60V (what my lab PSU goes up to). They are fine with those tests. Here...

19 replies | 183 view(s)

February 25th, 2021, 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...

19 replies | 183 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 | 393 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 | 393 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 | 393 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 | 393 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 | 393 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 | 393 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 | 393 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 | 393 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 | 393 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 | 393 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 | 393 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 | 393 view(s)