Hi all...
Yesterday after 3 months (!!) my new V9958 IC finally appeared into my mailbox, so I could start the VDP upgrade process of my NMS 8250, yay!! I want to do just this. No MSX2+ additional bios for the moment...
Well then, I started re-reading the MANY v9958 -> 8250 upgrade manuals I had already found (and read) months ago. Basically they all claim something like this:
1.- Let's propagate VDD (5V) from pin 58 to pin 21. (I'm getting 4.95 V, tested with my multimeter)
2.- Let's propagate GND from pin 1 to pins 4 and 27. (Sometimes I've seen some people propagating pin 20 instead of pin 1, which also tests as GND using a multimeter anyway)
3.- Let's Leave pin 26 floating (!?)...
Profit!
Well... Not really, as after doing all my homework with the wire wrap (soldering and reconnecting the pins described above: https://vimeo.com/350510393 ), I get glitchy images. The main symptoms I get are basically these:
1.- Image is HEAVILY shifted to the left. And when I say heavily, I REALLY mean it, as "set adjust (7,0)" does virtually nothing (I still miss like 8-10 chars in width 80 screen 0) It's close to unusability :(
2.- Blue signal is somewhat flaky, specially when there is A LOT of blue signal all over the image (and particularly on the borders, unconfirmed). When this happens the WHOLE image blue signal gets off, and thus blue becomes black, white becomes yellow, etc... i.e. MSX2 boot logo appears as yellow, floating in a black background (it's logical as the whole blue signal has disappeared). In extreme cases, the whole image gets 100% black (f1 spirit 3d konami logo for example)
I "can survive" with these glitches (well not that much, sofarun left column is close to 100% hidden), but I'd like to know what additional tweaks I might perform to have the crystal clear solid sync stability of my V9938.
I have to say I socketed the VDP on the NMS 8250 mobo, so I can put my V9938 back and forth wihtout any problem. V9938 is still working amazingly.
What is the nice thing of my recently installed V9958? -> F1-Spirit 3D, Laydock, etc... (the typical V9958 Screen 11/12 stuff) all work perfectly, so we can deduct the V9958 is really working ok, even some parts of the sync signal are not. My main suspects are CSYNC and HSYNC (pins 6 and 5) of the VDP.
BTW, before writing all this asking for hints, I've also tried to do additional homework... Let's see:
Looking for info about why all this might be happening, I found a dark remark (I can't remember where... Here on msx.org forums also? probably yes... whatever) that said something like:
-You should somehow stabilyze sync signals from the VDP in case you get wobbly rippling artifacts...
Well, am I really getting wobbly sync image/signal? Not at all. I mean, my image is HEAVILY shifted to the left, but is rock solid, it doesn't show any sign of rippling interference. Still more, if I touch pin 5, 6 and parts of the upper analog board (in charge of dealing with sync signal), THEN I'm getting silly wobbling and flaky signal and image. But as soon as I stop probing these circuit points, image gets rock solid stable again.
BTW, I also raised one leg of R167 and R166 (to effectively disconnect them), as it seems to be standard advice and procedure when upgrading to a V9958 (no one ever explains why though, electronic gurus are so prone to convey that halo of mystery and wizardry...) Well, no change whatsoever (connected or disconeccted, that is)
Speaking of which, I can also remember a still darker remark (by I can't remember who either), claming also something like this:
1.- Look for R357 on the analog top board (4K7 ohm) and rise its value to 10K (Again no explanation about why...)
I said, "well, let's see if it does something", and I just added a 3K3 resistor in serial to get an 8K resistor.
Did the sync signal got better? Not really... Of course, it's not the recommended 10K but at least I suppose I might have get some image enhancement of some kind: I got nothing.
Additional issues I remember while dealing with all this:
-If I carefully probe with my multimeter on pin 5 (HSYNC) of the VDP, image gets ONE PIXEL to the left (and it's still 100% stable). Whenever I stop probing said pin 5, image gets 1 pixel to the right. It would be amazing something could be done nearby pin 5 (adding some R or C) to get more right offset to the screen... No idea (?)
-If I probe with my multimeter on pin 6 (CSYNC), now image gets randomly distorted, not just ripply sync, but just random sync.
-If I probe WITH MY FINGER on the middle part of the ---[__4K7__]---finger---[__3K3__]--- serial resistor I created (to raise R357 value from 4K7 to 8K), then image sync gets wavy and a "vertical slow wave" of GOOD SYNC appears (!!?). It's difficult to explain without a video though, but you get the idea... (Maybe I will upload a video if I have the time).
It's somehow like a demo-scene effect: A vertical sinus wave slowly distorts the image (in a good way!) going from top to bottom. When some selected parts of the image get the "good" wavy distortion and they get moved to the right (in fact, where they should really appear), they also regain the lost blue color (!).
So maybe there's some additional tweaking nearby R357 that still needs to be done? I wish I knew more electronics...
Whatever, this post became a LONG ramble a while ago.
Any additional hint I might be testing? Any 8250 V9958 upgrade experts ?
Greetings and thanks in advance.
NOTE: I'm using the SCART RGB connection against a fantastic Daewoo 14" nifty and cute crystal clear CRT.
I have no available RF (in case it might be interesting to test different connection methods)
