an idea, fuse or coil powering the ps2 mouse port died .

weedeewee wrote on 2026-06-05, 12:06:

an idea, fuse or coil powering the ps2 mouse port died .

Is that fixable? How do I find out if it is that?

RetroPCCupboard wrote on 2026-06-05, 11:31:

Any ideas what might have happened? I don't think I changed anything between the time it worked, and when it stopped.

Did you by chance connect or disconnect the PS2 mouse while the system was powered on?

The PS2 port isn't designed for "hot plugging" and that could have damaged it.

Joseph_Joestar wrote on 2026-06-05, 12:33:

Did you by chance connect or disconnect the PS2 mouse while the system was powered on?

The PS2 port isn't designed for "hot plugging" and that could have damaged it.

Good suggestion, but no. It was on my testbench working fine. Turned off machine. Left it overnight. Came back in the morning, turned it on and was greeted with an error in windows saying there is no mouse.

RetroPCCupboard wrote on 2026-06-05, 12:26:

weedeewee wrote on 2026-06-05, 12:06:

an idea, fuse or coil powering the ps2 mouse port died .

Is that fixable? How do I find out if it is that?

Either figure out were the coil/fuse is on your mainboard and measure continuity on those, or measure if you still have +5v on your mainboard ps2 connector by using a multimeter and looking at the correct pinout. 😀

Is it fixable... depends on how proficient you're willing to be with a soldering iron, if that is the problem.

weedeewee wrote on 2026-06-05, 13:45:

Either figure out were the coil/fuse is on your mainboard and measure continuity on those, or measure if you still have +5v on your mainboard ps2 connector by using a multimeter and looking at the correct pinout. 😀

Is it fixable... depends on how proficient you're willing to be with a soldering iron, if that is the problem.

Ok. I will get out my multimeter and check for power on the port. Seems odd to me that the keyboard works, but not the mouse. I thought they were usually the same controller circuitry?

RetroPCCupboard wrote on 2026-06-05, 13:58:

weedeewee wrote on 2026-06-05, 13:45:

Either figure out were the coil/fuse is on your mainboard and measure continuity on those, or measure if you still have +5v on your mainboard ps2 connector by using a multimeter and looking at the correct pinout. 😀

Is it fixable... depends on how proficient you're willing to be with a soldering iron, if that is the problem.

Ok. I will get out my multimeter and check for power on the port. Seems odd to me that the keyboard works, but not the mouse. I thought they were usually the same controller circuitry?

In short, there are two issues under discussion.
1. If I replace the capacitors with polymer ones, will the universe collapse?
The answer is 42.

2. The mouse/keyboard have stopped working.
There are two types of capacitors at the inputs of these ports
- with COG/NP0 dielectric (Intel motherboards)
- all others.
The first type can withstand anything, but they are expensive.
The second type – as always.
When the second type starts to leak due to age, they short-circuit the mouse/keyboard signal lines. This is a common problem.
There may be either 4 separate capacitors or an array of 4 in a single package.
If there are any issues with them, simply delete them.

shevalier wrote on 2026-06-05, 15:46:

In short, there are two issues under discussion. 1. If I replace the capacitors with polymer ones, will the universe collapse? T […]
Show full quote

In short, there are two issues under discussion.
1. If I replace the capacitors with polymer ones, will the universe collapse?
The answer is 42.

2. The mouse/keyboard have stopped working.
There are two types of capacitors at the inputs of these ports
- with COG/NP0 dielectric (Intel motherboards)
- all others.
The first type can withstand anything, but they are expensive.
The second type – as always.
When the second type starts to leak due to age, they short-circuit the mouse/keyboard signal lines. This is a common problem.
There may be either 4 separate capacitors or an array of 4 in a single package.
If there are any issues with them, simply delete them.

You think a full recap is needed? I dont think any of the caps looked like they are bulging. But I haven't looked too closely. I have read that this board is prone to capacitor plague though

RetroPCCupboard wrote on 2026-06-05, 18:46:

shevalier wrote on 2026-06-05, 15:46:

In short, there are two issues under discussion. 1. If I replace the capacitors with polymer ones, will the universe collapse? T […]
Show full quote

In short, there are two issues under discussion.
1. If I replace the capacitors with polymer ones, will the universe collapse?
The answer is 42.

2. The mouse/keyboard have stopped working.
There are two types of capacitors at the inputs of these ports
- with COG/NP0 dielectric (Intel motherboards)
- all others.
The first type can withstand anything, but they are expensive.
The second type – as always.
When the second type starts to leak due to age, they short-circuit the mouse/keyboard signal lines. This is a common problem.
There may be either 4 separate capacitors or an array of 4 in a single package.
If there are any issues with them, simply delete them.

You think a full recap is needed? I dont think any of the caps looked like they are bulging. But I haven't looked too closely. I have read that this board is prone to capacitor plague though

These two questions come up at least once every two weeks.
Ideally, these two topics should be pinned (for those who don’t know how to use the search function)
4х capacitor array
It’s not clear from the photo whether this is a capacitor array. If so, it needs to be either removed or replaced.
1x1 – fuse; L1–L6 – ferrite beads.
Check their resistance; it should be around 0 (definitely less than 1 Ω).

Its ABit KT7A, electrolytic caps are pretty much a given, but 99% not related to ps2 issue.

For the ps2 start with multimeter checking if those two green fuses next to PS2 port are ok, and check with different PS2 mouse, maybe it just died.

rasz_pl wrote on 2026-06-06, 05:40:

Its ABit KT7A, electrolytic caps are pretty much a given, but 99% not related to ps2 issue.

For the ps2 start with multimeter checking if those two green fuses next to PS2 port are ok, and check with different PS2 mouse, maybe it just died.

Thanks for the reply. The fuses are showing 0.2ohms resistance. I have tried 3 mice. One optical, two ball. None work.

shevalier wrote on 2026-06-06, 04:54:

4х capacitor array It’s not clear from the photo whether this is a capacitor array. If so, it needs to be either removed or repl […]
Show full quote

4х capacitor array
It’s not clear from the photo whether this is a capacitor array. If so, it needs to be either removed or replaced.
1x1 – fuse; L1–L6 – ferrite beads.
Check their resistance; it should be around 0 (definitely less than 1 Ω).

The fuses I think are ok (almost no resistance between legs).

The L1-L6 are 0.1-0.2ohms.

I guess that just leaves the C470 capacitor array. The resistances seem to be different on all pins. Between 1k and 5k.

RetroPCCupboard wrote on 2026-06-06, 06:17:

I guess that just leaves the C470 capacitor array. The resistances seem to be different on all pins. Between 1k and 5k.

This is the first sign that there is a problem with this capacitor array.
All resistance to grownding should be identical, because all the signal lines to the mouse and keyboard are exactly the same.

Although, I don’t know why, it is specifically resistor arrays that are prone to having one component fail.
There may be issues with them too, but this is far less likely.

shevalier wrote on 2026-06-06, 06:31:

This is the first sign that there is a problem with this capacitor array. All resistance to grownding should be identical, becau […]
Show full quote

RetroPCCupboard wrote on 2026-06-06, 06:17:

I guess that just leaves the C470 capacitor array. The resistances seem to be different on all pins. Between 1k and 5k.

This is the first sign that there is a problem with this capacitor array.
All resistance to grownding should be identical, because all the signal lines to the mouse and keyboard are exactly the same.

Although, I don’t know why, it is specifically resistor arrays that are prone to having one component fail.
There may be issues with them too, but this is far less likely.

Ok. Thank you. I will have a go at removing it with my air soldering station. I am still a novice at using it, but did successfully replace surface mount RAM chips on my Pocket 8086 a while ago

I'd guess some flexing of the board when putting some strain on the connector by tugging on the mouse/keyboard cable or bumping them could lead to damaging the MLCCs.

weedeewee wrote on 2026-06-06, 08:05:

I'd guess some flexing of the board when putting some strain on the connector by tugging on the mouse/keyboard cable or bumping them could lead to damaging the MLCCs.

No. The potential difference there is slowly damaging capacitors with Z or Y dielectrics.

ps2 failure on 1 port, but not the other doesn't scream recap, but all these boards are on borrowed time. the last time i owned an abit kt7a-raid was 20yrs ago so i don't have experience with how well the design holds up to capacitor deterioration. i do own a couple contemporary kt7a iwill boards and the design is very tolerant as the capacitors are a total exploded mess and they still both boot into windows when tested (on the other hand i have an amd761 board with no bulging caps that won't even post). i ascribe this miraculous feat to having an exceptionally good psu on my testbed. you might try testing your rails or swapping out your psu if you don't have a scope as a quick & dirty test.

shevalier wrote on 2026-06-06, 06:31:

This is the first sign that there is a problem with this capacitor array. All resistance to grownding should be identical, becau […]
Show full quote

This is the first sign that there is a problem with this capacitor array.
All resistance to grownding should be identical, because all the signal lines to the mouse and keyboard are exactly the same.

Although, I don’t know why, it is specifically resistor arrays that are prone to having one component fail.
There may be issues with them too, but this is far less likely.

Ok. Well I have now removed that capacitor array. I practiced removing SMD components from a dead GPU first. It took about 25 seconds of heating before it came off.

The mouse now works! Many thanks All.

On the subject of recapping, this is what they currently look like:

The capacitors look fine but they may still be in need of replacement. With new caps and socket pin mod, you should be able to get up to 2.3-2.4 Ghz.

If it runs fine for what you are using it for, don't worry about it. Most of those large caps are for CPU and maybe RAM.

The last KT7A board I got that was NOs, the first time I powered it up, most of the caps exploded. Made me jump and there was capacitor paper all over the place.