I Finally Got a Socket 7 Motherboard !

[opa]

Pre-yellowed for your convenience!

If I get one I'll let you know if a USB to PS/2 adapter works.

[Ziggy587]

Thanks.

So that NOS keyboard I ordered came in today. It's even better in person. The cable has that spiral elastic segment in the middle, like old school keyboard cables use to have. And it weighs a lot, there's a metal back plate inside. Which means it wont be sliding around at all.

BUT, it's not working.

Well, at least, I cannot confirm if it's working or not. It has the AT style 5-pin DIN connector, and the Socket 7 mobo is the only thing I currently have that accepts that keyboard connector. But the other day, when I first went to test this mobo, the first keyboard I grabbed wasn't working. An IBM KB-9930 which is PS/2 (I have a PS/2 to 5-pin DIN adapter). I found that odd since this IBM keyboard worked the last time I used it. So I grabbed whatever random PS/2 keyboard, which was a more modern lightweight Compaq keyboard. But now that this NOS Acer keyboard isn't working, I'm suspecting maybe something is wrong with the motherboard.

I probed the voltages, and the +5v rail is measuring at 4.85v off the motherboard (the PSU is putting out slightly over 5v when it test it by itself). I Googled it, and most sources say that ATX tolerance is +/- 5%, which would be 4.75v. So 4.85v is within spec. I was thinking that maybe the IBM and Acer keyboard are more power hungry which is why they're not working, but the more modern Compaq keyboard was able to run under 5v. But if ATX specifications allow for as little as 4.75v on the 5v rail, than you would think keyboards should also allow for that tolerance. I opened up the Acer keyboard just to see if there was anything obvious going on (swollen or exploded caps) but it looks clean. But strangely, I probed the connector on the PCB inside the keyboard and couldn't find 4.85v, it was measure somewhere between 3 and 4 volts. So I don't know what's going on there, I'll have to investigate more.

I'm going to order an adapter that let's you use the 5-pin DIN keyboard on a PS/2 port (I only have the reverse adapter) so that I can test the Acer keyboard on other computers.

4.85v is within spec, so I'm not super concerned. It's possible that both the Acer and IBM keyboards are broken. But I was debating whether or not I wanted to recap this mobo. This board is pre Capacitor Plague, but it's still 25+ years old. There isn't too many caps, and they're all through hole so they'll be easy to change (as oppose to SMD caps). I was sort of leaning toward not recapping, but now I might be leaning toward recapping.

With replacing electrolytic capacitors, there seems to be two camps. One says just go ahead and recap something, it's only a matter of time before the caps age and go out of spec or leak. The other says if it's working then don't recap because you're needlessly risking damage (there's always a chance of damage no matter how good you or your equipment is). But I think you just have to consider what it is your talking about. There are some very cheaply manufactured PCBs that you can very easily lift pads/traces on, so that might not be worth recapping if it's still working. But a Biostar motherboard made in the 90s I would suspect to be made well enough that you don't have to worry if you know what you're doing. Too bad they don't specify the substrate in the consumer manual LOL.

I should also try another power supply. The one I'm using is basically brand new, but it's not exactly high end. It's a cheap EVGA that I bought a few years ago specifically for when I need to test things out. And that's all I've ever really done with it, test things out for minutes at a time. I have other power supplies on hand, of course, but they're either in other systems or may not be totally reliable. I suppose I have to eventually get a dedicated power supply for this build anyway. I guess I was waiting until I found a case before worrying about the PSU.

edit: Well I found a female 5-pin DIN to mail PS/2 adapter on eBay that ships from Long Island, so I should know soon enough if it's the keyboard or the motherboard. I know I can take the PS/2 cable off of a keyboard and solder it on to the Acer, but I'd rather not hack up my new keyboard just yet.

[Ziggy587]

You know, I have so much old PC crap that I haven't looked at in years, I really forgot that I had some items. I actually just found a Socket 7 CPU that I didn't know I had. It's a Pentium MMX 233 Mhz. I'm pretty sure it's compatible with this board. I really have no memory of where I got this CPU. Ultimately I want to use this as an over spec DOS machine (because 486 crap is too expensive) so this 233 MMX will be too much for that. But I like to tinker. So at some point I'll have to swap it in and see how much I can push this board as a Windows 9x setup. After all, half the fun of owning old computers is swapping out parts.

I had gotten rid of pretty much all of my stuff that was pre-Pentium II, but I knew I had two random SIMM RAM sticks. Out of curiosity I just plugged them into the mobo and they are compatible! Turns out they are 64 MB (2x 32 M). On these turn-of-the-era boards that support both SIMM and SDRAM, I've always been curious if you can use both types of RAM at the same time, or if you have to use one or the other. Well, I plugged in both types and RAM to find out. The mobo POSTs and reports the correct amount of RAM. Interesting!

[Ziggy587]

I seem to be getting all of the really important parts for this build. First I got a keyboard, and now a mouse!





I wanted a really no-frills 90's looking ball mouse for this build, and I came across this NOS one. It's nothing special, it's a PC Concepts Aero. Maybe it sucks? But it was cheap, and it comes with a driver floppy and a weird mouse pad. The mouse pad is some anti static thing, maybe it also sucks, but we'll see. But I like getting new old stock stuff, especially when it comes with a driver disk/disc. It was cheap enough that even if the mouse pad is garbage (as I suspect it might be) it still would have been a good deal for a NOS mouse.

[marurun]

So, the sound card appears to be an SB32 PNP (CT3600). Both RAM slots are populated.

[Ziggy587]

So, the sound card appears to be an SB32 PNP (CT3600). Both RAM slots are populated.

Thanks for digging it out!

So it looks like this?

So from a little bit of reading, this model is known as "Sound Blaster 32" and is a sort of budget AWE32. Wikipedia states that if the RAM is installed then the sampling is identical to the AWE32. And the SB32/AWE32 share the same drivers. One downside though is that it's missing the Wave Blaster header. I'm planning on getting the DreamBlaster X2GS, which plugs into that header. So I think I'll have to pass. But thanks for pulling it out for me. And by all means, if you have any other stuff lying around you wouldn't mind parting with, let me know!

[opa]

dang it, ziggy, you've got me browsing ps/2 mice on ebay LOL

[Ziggy587]

OK, so unfortunately, I think there's a problem with the motherboard.

I'm seeing power issues at the PS/2 and keyboard ports. Two different PS/2 keyboards wouldn't work at all, and I think it's because they're not getting enough power. I guess I was lucky enough to find a keyboard that is OK running with low voltage.

I tried a different PSU to be sure, and that's definitely not it. Measuring the 5v rail on spare Molex connectors reads 5.08v. If I plug in just the keyboard, it works. If I plug in that same keyboard and a PS/2 mouse, then neither will work. If I plug in just a PS/2 mouse without the keyboard, the mouse still doesn't work.

I measured the voltage at the PS/2 port while the keyboard was plugged in. It measures differently depending if the num/cap/scroll locks are on (when they're on, an LED is on which is drawing more power). For example, with no lights on I get 3.752v at the PS/2 port. With just num lock on, I get 2.19v. With all three lights on I'm getting only 1.905v! If I disconnect the 5-pin keyboard, I get 5.04v at the 5-pin port. I can't probe it while I have a keyboard plugged in, unless I take a keyboard apart which I don't feel like doing right now, but I suspect the voltage is lower when the keyboard is plugged in (I measured it the other day and IIRC it was around 3.5v).

Anyone have any ideas? There's definitely some sort of power issue going on with this board. I'm mean, I'm assuming it isn't normal for PS/2 ports to be as low as 1.9v on the 5v pin LOL. It would be a shame if I end up having to return this board to the seller. I'd rather fix it, if possible.

The weird part is that everything else seems to be working just fine. I hooked up a HDD and CD drive and actually installed Windows 98 SE without any issue. I can boot to the desktop. The only issue I'm seeing is at the keyboard and mouse ports.

dang it, ziggy, you've got me browsing ps/2 mice on ebay LOL

There's quite a few NOS Logitech 2-button beige ball mice on eBay for not so much. In fact, I might pick one up! I have one, but it's dirty. It would be nice to have a new one!

[opa]

I'd probably return it if it were me TBH
Do you get a different voltage reading on the ps/2 if an hdd is plugged in and running? Just spitballing here... It shouldn't really impact it but you never know with these old things.

Edit
Do your traces look fine?

[Ziggy587]

I'd probably return it if it were me TBH

Yeah, I mean, at the end of the day it was still a great price for the motherboard and CPU bundle. So if the problem is easy and cheap to fix, then it'll still be worth it. But if the problem turns out to be like a blown controller IC or something, and a replacement part is impossible to find or crazy expensive, then yeah I would have to return it.

And really, with vintage boards like this, you kind of have to expect to run into issues like these. For example, I found a new old stock video card that I picked up for cheap (I will probably be posting a separate thread for it). Although it was brand new, when I got it I noticed a swollen cap. Luckily they're through hole caps, and not many of them, so I decided to recap it. The seller probably wouldn't give me any hassle if I requested to return it. But for the price I paid, I don't mind having to recap it. For me, that's part of the hobby. But I understand not everyone is capable of doing recaps or investigating repairs.

Do you get a different voltage reading on the ps/2 if an hdd is plugged in and running? Just spitballing here... It shouldn't really impact it but you never know with these old things.

Edit
Do your traces look fine?

I posted this problem on the Vogons forums and am getting a lot of help there. Luckily, there really aren't many components between the +5v rail and the KB and PS/2 ports. I ended up tracing it out last night. From the +5v rail it goes to an electrolytic cap, then to a fuse, then to a small inductor, and then to the power pins of the KB and PS/2 ports. The fuse seems OK. At least, it has continuity so I know it isn't blown. But a few people have suggest that it could be on the verge of blowing and acting as a resistor causing a voltage drop. But I think it's the inductor that's the issue. It's reading 6.14 K ohms, while it should have very low resistance. So I'm pretty sure the issue is there. It has been suggested that it's safe to bridge the inductor (it's only there to reduce noise) as a way to test. If the problem goes away, then that's definitely what it was. I'll order a new inductor to replace it. It could probably stay bridged indefinitely without any ill effect, but I'd rather replace it. I might order new fuses too, since this one might have been getting hammered over 30 years.

So hopefully that's all it is. If I'm not too tired tonight, I'll see if I can bridge that inductor and test it out.