16 KILO ohms? that's hardly a short

maxtherabbit wrote:

16 KILO ohms? that's hardly a short

I agree, but compared to the 12V and -12V lines, which are in the range MegaOhms, it is an outlier.

I checked the same pins on a couple of other ISA cards I have lying around (SB16, etc) and their 5V lines have several megaohms resistance to ground.

I am testing this card in a 16-bit ISA slot on a Pentium MMX 200MHz system. Would there be any sort of compatibility issues that I may have missed? I ran a Sound Blaster 1.5 perfectly fine in this system, so I figured the Adlib would be fine.
It has an ATX power supply, so I assume it's not powering up in order to protect itself.

This is a genuine card, the first thing to replace are the tantalum caps as they are known to go bad . Remove them and see if the resistance changes.

keropi wrote:

This is a genuine card, the first thing to replace are the tantalum caps as they are known to go bad . Remove them and see if the resistance changes.

This seems like a very good idea!

Also, you can repair it since it's fairly easy to get replacements for all the components. Good luck saving this beauty!

crazybubba64 wrote:

I'm also not sure if it is genuine or not, as it seems to be a very early revision (1987) and I haven't seen many pictures online of this exact variant.

It's indeed the first revision, though this card was made in December of 1989. Probably one of the last cards of the first revision ever made, since in 1990 the new revision came out. That's quite interesting, because based on the serial number, we can therefore assume that about 20.000 cards of the first revision were made.

I agree, but compared to the 12V and -12V lines, which are in the range MegaOhms, it is an outlier.

No, it's not. It's Ohm's law. The card mostly uses 5V, so naturally the resistance of the 5V rail against GND is lowest.

Replacing the tantalum caps should be the first task, however, just as keropi suggested. They often fail after such a long period of time.

16k is not only "not a short", but is high enough impedance that I wonder if your reading is correct. It's not uncommon to find cards that read as a few hundred ohms. A populated motherboard might show readings in the tens of ohms.

Meg-ohm is practically open-circuit. 😀 If that's correct, then either it has no significant circuitry on the 12V rail (not even a pull-up/-down resistor) or it's blown open.

When a tantalum cap goes bad, it usually shows a rail-to-ground impedance of anywhere from 0.x ohms, to maybe around 5 ohms. Bear in mind, if the board has bulk capacitors on it, it may show a short until those caps are charged. Depending on your meter, there may not be enough supplied current to charge them.

So, I would question whether those readings are accurate, but replacing the tantalum caps is probably a wise idea anyway. If they haven't failed yet, they probably will. If that doesn't fix it, don't sweat it. Everything on an Ad Lib is a commodity part and can be replaced.

Thanks for all of the help. I'll get the tantalum caps on order and try to get them all replaced nicely.

As for the values of the capacitors, I assume the modern Adlib kits are using the same values? If not, has anyone documented them?

The parts are usually self-documenting. Those little orange tantalum caps will have numbers etched on them that define the voltage rating and capacity.

crazybubba64 wrote:

Thanks for all of the help. I'll get the tantalum caps on order and try to get them all replaced nicely.

As for the values of the capacitors, I assume the modern Adlib kits are using the same values? If not, has anyone documented them?

the radlib et al. are meant to be 100% exact clones AFAIK, so you should be safe to use the values from those BOMs

crazybubba64 wrote:

As for the values of the capacitors, I assume the modern Adlib kits are using the same values? If not, has anyone documented them?

http://tubetime.us/index.php/2016/07/22/a-rep … lib-sound-card/