SVI 328 VRAM Replacement and Disaster Strikes (Part 2) 

Thank you! Really glad to hear that!

I'd like to echo this, I'm not even into retro computing and I love watching these videos. You've got a great presentation style Noel.

@@stevefreegard6406 Thank you! I really appreciate it!

I second that too - I like the presentation style, the voice, the quality of the video and the overlays and that all the steps are documented and explained (including mistakes) but without getting boring. Thank you!

I'm glad you're enjoying it so much. I'm hoping that by putting all my mistakes along with the advances, it makes for an interesting video and we can all learn from it :-)

Thank you so much! Really happy to hear when someone becomes more interested in retro electronics after watching one of my videos 😃

That's the spirit! :-)

In a couple of days I'll be posting a video with some related updates, but don't worry, it's going forward. Whenever the video comes up you can laugh at me for... getting the wrong VDP the first time around :-b The correct one is on its way, so hopefully I'll wrap this up in a week or two.

It does look like that from the picture because of the angle of the wire, but the link is correct. I'll post an updated picture. And most importantly, I checked continuity on the connections like 10 times in that area.

4164s aren't exactly modern, but they're for sure much more easily available than 4116s and much easier to work with. So yeah, big win there 😀👍

@@NoelsRetroLab At least we can still buy it, but sadly in reality, nothing last forever.

Yes, I noticed the pads were totally missing, so there was nothing to solder it against. It was just held with the wire on the other size, which was at least soldered correctly to the crystal. Working on a board that someone destroyed is quite frustrating.

Thanks for the tip. Which solder spikes do you refer to? Can you point me to the time in the video? Just curious. I usually don't add extra flux because the solder I use have a lot of flux already. But you're right that in cases where I'm combining old solder it might be good. What kind of flux do you recommend? The pasty kind of the clear liquid one?

@@NoelsRetroLabclear liquid is much easier to clean. The rosin style is annoyingly sticky.

I thought about it, but I doubt it. All it could do is connect the address/data/control lines to other parts of the chip. The only output is data out, which flipped would be connected to A5, and I doubt it would cause any damage (and chances are it wasn't even enabled as output). The RAM chip on the other hand could have well been damaged swapping VCC and ground, but apparently it was sturdy enough.

Sure, but I'd still prefer to take down what's in there to know exactly what's going on. If this happens, it's all part of the learning process.

Ah, interesting! I've been trying to get better about wearing the anti-static wrist band, but I didn't ground the board itself. I'll make sure I do that when I get the replacement. Thanks!

It was before any ESD protection was implemented, so wrist bands are not an option if you want to work on those things.

@@NoelsRetroLab don't head down the popular misconceptions involving "ground". The ESD issue is related to the "potential difference" between you, your tools (iron etc) and whatever you are working on. The only thing "ground" has to do with it is that it is usually the common connection point between your soldering station, your ESD strap and your ESD dissipative mat. Not much point wearing a strap when the PCB is scooting around on a plastic work mat generating lots of static so you should really get a work mat as well (like Jan Beta!). I've seen various videos where people have made a song and dance about "I'm wearing my strap and it is connected to ground", yeah good for them but that does NOTHING to protect what they are working on unless it is also effectively connected to ground as the common point. The other nonsense idea people have is that due to its age this gear is not susceptible to ESD damage, that's a fantasy that will cost them in the long run. I did my first formal ESD training course with IBM in the early eighties and the most recent professional refresher last year. Even the 1960s NASA documentation lists ESD precautions relating to electronic modules (which were ignored by a popular YT group restoring lots of precious Apollo gear!!). Save your precious collectibles and invest in a mat, strap and ensure you don't use nasty plastic bins and takeaway food containers to store ESD sensitive parts (like the ebay glad wrap packing of 4164!!!!).

@@ingmarm8858 I actually started looking into it a while back and didn't come up with a clear conclusion. Those grounded mats seem to be only conductive on the underside (as they should, otherwise it would be horrible). How exactly does that help equalizing the potential difference of the board being worked on? (It's a serious question, I'm not impliying it doesn't). And the followup question: If I'm grounded and pretty much constantly touching the board as I'm repairing it, isn't that enough to keep the potential close to equal? Thanks!

@@NoelsRetroLab the proper bench mat material has a top and possibly bottom "dissipative" layer, i.e. it will not hold a static charge and any static charge will dissipate into the conductive layer and of course the internal layer or bottom layer is conductive. The equalisation can only happen if all these things are bonded together and that is where ground is useful. So in my case at home where I don't have ESD flooring (unlike work) I have matting right along my work bench and yes it is "grounded" via a special ground only plug and typically 1M resistor. Then my wrist strap is also connected to that common grounding point. This way I stay at the same potential as my work bench and any mains grounded equipment like soldering irons, bench supply and whatever I am working on is already on the mat and will not build up a static charge (relative to me or ground). You can take it as far as you want, obviously the material your clothes are made out of can make a difference, the humidity etc etc. If you maintain constant contact with what you are working on then yes just a strap will help but the risk of discharge is then between you and the device and say your plastic bench mat or real ground or your chair. That is why I'd encourage to get a mat, strap and ground connection. It only takes 50v or less to damage (ref IBM training) something that does not have integral ESD protection (like modern chips do). You won't even notice that sort of static discharge.

Except that I'm the one trying to revive it and it keeps dying on me :-) But stay tuned because in today's Mail Day video there's a big update about this project and I should be able to wrap it up next week. So yes, it's finally coming.

Probably, but I haven't tested it. It would make sense, but it could even be one of those things that is left to the implementation of the actual memory chip? Not sure, but it felt a lot safer to cut it (or bend it if you really don't want to cut it).

@@NoelsRetroLab Absolutely, better safe than sorry. It would be interesting though to do a test on one of the chips, applying say 5V to Pin 1 and then testing the chip afterwards to see if it still functions. I have no idea myself, but one would think that if a pin is NC then literally the physical pin would just be a dummy pin with absolutely no internal connectivity. But like you, I don't know if that is the case or not.

@@Ikrananka Yeah. Or even better, feed it 5V from a bench power supply and see what kind of current draw it has. If it's significant at all, bad things will happen :-) But you're right, I expect it to be disconnected internally.

🤣🤣

It should have been linked at 00:26, but here's the link to the full MSX/SVI playlist: ru-vid.com/group/PLmbYPqkyiASxP3MVx_3yBTu30o0egZGpF

I was told that, and I agree that it looks that way, but I checked and it's connected correctly. It looks like that because of where the housing of the cable ends, it looks like it's soldered to the wrong place. Thanks for the heads up though.

@@NoelsRetroLab Ok, waiting for the follow up :)

@@fabioacrs I'm waiting on th replacement VDP. You'll see it in the video, but I ordered one and it seemed to work but... I accidentally ordered an NTSC one! Doh! So I'm waiting on the PAL one. Should arrive any day now.

Haha, fair enough. The oscillator tracks are horrible because it's completely missing the pads, so it's attached the best I could without getting into a bigger production. And my wire job isn't the best either :-) No tweaking of the trimmer would change it though. I did verify later that it was the VDP, so at least that's finally working. But yeah, this could definitely be improved.

Because the chip completes the oscillating circuit. Look at the circuit I made to test it. The chip sort of implements the two inverters (or whatever circuit they actually implement). That's why the chip has connections to the crystal on both pins 39 and 40. If you remove the chip (or if it's faulty), you get no clock signal. You're right about bad solder joints and I actually did reflow them all off camera to be sure, but still nothing, that's why I'm leaning towards a bad chip. But who know, maybe I'll get a new one, replace it and it won't still work.

@@NoelsRetroLab Ah, didn't know it was implementing the divider circuit. I am going to say I doubt the chip died, unless you shorted something out its a bit unlikely. I'd make sure its getting voltages and such. Also ohm out the various pins. I'm sure it'll be something simple. I ran into this when fixing my Amiga 2000, now I can generally pin down faults by looking at them =)

@@thomasandrews9355 Yeah, I'm not hopeful about the new VDP, but it's the only lead I have right now. I checked the connections around the crystal like 10 times (since that's the last thing I messed with when this happened) and they check out fine. I also pulled out all the VRAM in case something there was shorted, but nothing. I suppose I can take out the VDP and put in a socket. That might be enough to catch some small short or a bad solder joint. Might do that if the VDP takes too long to arrive.

@@NoelsRetroLab Okay, I'm reading the schematics, I see XTAL1 and XTAL2 are connected to a capacitor RC network? Thats actually what the yellow thing is, a variable cap, looks like 50pf? I think this is entirely a circuit issue, I'd review hansotten.file-hunter.com/uploads/files/STM-A_SVI318-328.pdf page 6, under system clock. Verify no caps are shorted. The crystal I'd imagine should still put out a signal, just not oscillate. Start there.

@@thomasandrews9355 That's the doc I've been using. The exact schematic is in page 37, because this is a MK II version. The clock circuit is very slightly different. Those capacitors and resistors are the ones I've checked for connectivity a bunch of times and they're fine as far as I can tell. The crystal puts out a small oscillation on pin 39 (see towards the end of the video). Oh how I wish I had a working 328 side by side to compare signals and swap chips. It's so much easier when you have a working machine! :-)

I know, right? On the other hand, I couldn't let those wires with exposed metal hanging out back there alone :-)

It's the t-shirt for a game I made a while back subterfuge-game.com

@@NoelsRetroLab Oooo, you're a sneaky tricksy one. Well played, I suppose :'D

Good catch. You're right! I think I missed that extra connection in the diagram in the middle from the output of the first inverter to the point in between the two resistors. Gracias! 😃