If you're lucky it may be a broken solder joint. Did you check continuity between the PS2 connector and the pins on the bottom of the motherboard? Did you try with a different PS2 keyboard? It may be the keyboard/cable/connector too.

tauro wrote on 2025-01-26, 06:43:

If you're lucky it may be a broken solder joint. Did you check continuity between the PS2 connector and the pins on the bottom of the motherboard? Did you try with a different PS2 keyboard? It may be the keyboard/cable/connector too.

Seems like I am not so lucky. Tested the continuity across all the PS/2 pins and it was fine. Already tried with a different PS/2 keyboard with the same result. With one keyboard there are 3 leds lit up for a second at board startup. With the other keyboard, there is no light lit up at all. I am doubting if it could the capacitor as few caps were severely bent on arrival.

Check the keyboard fuses for resistance. I once had a weird failure mode on one of my motherboards where the keyboard fuse tested okay for continuity, but the resistance was crazy. Replacing the fuse with a simple wire link confirmed that it was indeed the fuse (which had not failed 'open' as you would expect).

stealthjoe wrote on 2025-01-26, 09:30:

tauro wrote on 2025-01-26, 06:43:

If you're lucky it may be a broken solder joint. Did you check continuity between the PS2 connector and the pins on the bottom of the motherboard? Did you try with a different PS2 keyboard? It may be the keyboard/cable/connector too.

Seems like I am not so lucky. Tested the continuity across all the PS/2 pins and it was fine. Already tried with a different PS/2 keyboard with the same result. With one keyboard there are 3 leds lit up for a second at board startup. With the other keyboard, there is no light lit up at all. I am doubting if it could the capacitor as few caps were severely bent on arrival.

You probably should check all the electrolytic caps and see if they are within spec (capacitance and ESR). Hopefully that's it!

megatron-uk wrote on 2025-01-26, 11:00:

Check the keyboard fuses for resistance. I once had a weird failure mode on one of my motherboards where the keyboard fuse tested okay for continuity, but the resistance was crazy. Replacing the fuse with a simple wire link confirmed that it was indeed the fuse (which had not failed 'open' as you would expect).

Any idea of what should be the maximum acceptable resistance across the fuses? My understanding is that any resistance above 50 ohms would fail continuity test anyway (no beeps).

stealthjoe wrote on 2025-01-26, 11:13:

Any idea of what should be the maximum acceptable resistance across the fuses? My understanding is that any resistance above 50 ohms would fail continuity test anyway (no beeps).

Should 1 ohm or less.

Just measured the resistance of the fuses and they were all 0.7 ohm. Also one cap circled below measured capacitance ~500uF (actual 1000uF). Wondering if this could be a concern.

Try checking the voltage across the fuse when the system is turned on with a keyboard connected.

stealthjoe wrote on 2025-01-26, 12:25:

Also one cap circled below measured capacitance ~500uF (actual 1000uF). Wondering if this could be a concern.

The attachment IMG_20250126_175409.jpg is no longer available

I'd say yes. It's way off. The tolerance is ±20%. You should replace that capacitor (and probably all of them). ESR should be very low too.

I can see 2 RN above the big yellow ring inductor. Do they test ok?
Also L1-L5, all 0.xx ohm?

https://theretroweb.com/motherboards/s/soltek-sl-65kv2

Does it work with a USB keyboard?

stealthjoe wrote on 2025-01-26, 12:25:

Also one cap circled below measured capacitance ~500uF (actual 1000uF).

How did you measure the capacitance of this electrolytic cap? Did you desolder it from the PCB? If not, then it is not certain that these 500 uF are the real value.

Nexxen wrote on 2025-01-26, 17:58:

I can see 2 RN above the big yellow ring inductor. Do they test ok?

Can you please explain more on the 2 RN (resistors?) you are referring to and how to test it?

Nexxen wrote on 2025-01-26, 17:58:

Does it work with a USB keyboard?

It does work with a usb keyboard. However the system is literally unusable as many DOS games freeze/slow down significantly while using the keys.

stealthjoe wrote on 2025-01-27, 00:48:

Nexxen wrote on 2025-01-26, 17:58:

I can see 2 RN above the big yellow ring inductor. Do they test ok?

Can you please explain more on the 2 RN (resistors?) you are referring to and how to test it?

Check the stuff in pic. Let's hope it's something wrong here.
I'm convinced it's a dead cap or other smd.
You could try by pressing down the chipset, being the only other component that has to do with the keybaord signal.

The 472 should be a pull up resistor network, on the other side if I'm correct (and I doubt) it shoul dbe +5V

Nexxen wrote on 2025-01-27, 01:44:

Check the stuff in pic. Let's hope it's something wrong here. I'm convinced it's a dead cap or other smd. You could try by press […]
Show full quote

Check the stuff in pic. Let's hope it's something wrong here.
I'm convinced it's a dead cap or other smd.
You could try by pressing down the chipset, being the only other component that has to do with the keybaord signal.

The 472 should be a pull up resistor network, on the other side if I'm correct (and I doubt) it shoul dbe +5V

I just checked the resistor array and the values were 000 for RN1 and 472 for RN2. Measured them and it was ~1 ohm for 000 array and 4.5k ohm for 472. So I guess it is within the limits.

Now coming to the inductor. There was continuity across L1, L3, L4 and L5. L2 had absolutely no continuity. To double check, I measured the resistance and it was OL for L2. For others it was 1 ohm or less. So I am assuming that L2 is at fault.

Now for the next question, how do I determine the value for the L2 inductor as there are no values on them? Also any other alternative for replacing L2?

stealthjoe wrote on 2025-01-27, 03:11:

I just checked the resistor array and the values were 000 for RN1 and 472 for RN2. Measured them and it was ~1 ohm for 000 array […]
Show full quote

Nexxen wrote on 2025-01-27, 01:44:

Check the stuff in pic. Let's hope it's something wrong here. I'm convinced it's a dead cap or other smd. You could try by press […]
Show full quote

Check the stuff in pic. Let's hope it's something wrong here.
I'm convinced it's a dead cap or other smd.
You could try by pressing down the chipset, being the only other component that has to do with the keybaord signal.

The 472 should be a pull up resistor network, on the other side if I'm correct (and I doubt) it shoul dbe +5V

I just checked the resistor array and the values were 000 for RN1 and 472 for RN2. Measured them and it was ~1 ohm for 000 array and 4.5k ohm for 472. So I guess it is within the limits.

The attachment IMG_20250127_080548.jpg is no longer available

Now coming to the inductor. There was continuity across L1, L3, L4 and L5. L2 had absolutely no continuity. To double check, I measured the resistance and it was OL for L2. For others it was 1 ohm or less. So I am assuming that L2 is at fault.

Now for the next question, how do I determine the value for the L2 inductor as there are no values on them? Also any other alternative for replacing L2?

OL means unlimited resistance?
They should be around 1 ohm all (or less), they have no res by design. In this case they act as filters (if I am correct).
You can just desolder it and put any kind of connection (solder blob or a wire), just to test.

Before doing anything, check if it connects to the keyboard ps2 port. Continuity check 😀
It's always checking stuff... 🤣

Nexxen wrote on 2025-01-27, 03:36:

OL means unlimited resistance? They should be around 1 ohm all (or less), they have no res by design. In this case they act as f […]
Show full quote

OL means unlimited resistance?
They should be around 1 ohm all (or less), they have no res by design. In this case they act as filters (if I am correct).
You can just desolder it and put any kind of connection (solder blob or a wire), just to test.

Before doing anything, check if it connects to the keyboard ps2 port. Continuity check 😀
It's always checking stuff... 🤣

OL usually means there is an open circuit. I tested the continuity between the keyboard PS/2 pins and the start of inductors L2 and L3 and it was present. To do a smoke test, I just shorted a pair of tweezers over the L2 terminals and switched ON the board with the keyboard connected. Guess what, the keyboard finally sprung to life!! The Num Lock LED lit up and proceeded through the BIOS without any errors. Hoooray!!! Thank you so much Nexxen!!!

Now for the permanent approach, I am thinking of using a tiny wire to solder over the L2 terminals without removing the inductor. My query is will there be any long term issues with this solution without the use of an inductor? I tried measuring the other inductor values using a basic LCR meter (with a selection knob). I set the knob at 20mH (the lowest available option) and it read ~0.5mH. Not sure if it is accurate though as I am unable to find any smd inductors for purchase with this value.

stealthjoe wrote on 2025-01-27, 07:39:

Nexxen wrote on 2025-01-27, 03:36:

OL means unlimited resistance? They should be around 1 ohm all (or less), they have no res by design. In this case they act as f […]
Show full quote

OL means unlimited resistance?
They should be around 1 ohm all (or less), they have no res by design. In this case they act as filters (if I am correct).
You can just desolder it and put any kind of connection (solder blob or a wire), just to test.

Before doing anything, check if it connects to the keyboard ps2 port. Continuity check 😀
It's always checking stuff... 🤣

OL usually means there is an open circuit. I tested the continuity between the keyboard PS/2 pins and the start of inductors L2 and L3 and it was present. To do a smoke test, I just shorted a pair of tweezers over the L2 terminals and switched ON the board with the keyboard connected. Guess what, the keyboard finally sprung to life!! The Num Lock LED lit up and proceeded through the BIOS without any errors. Hoooray!!! Thank you so much Nexxen!!!

Now for the permanent approach, I am thinking of using a tiny wire to solder over the L2 terminals without removing the inductor. My query is will there be any long term issues with this solution without the use of an inductor? I tried measuring the other inductor values using a basic LCR meter (with a selection knob). I set the knob at 20mH (the lowest available option) and it read ~0.5mH. Not sure if it is accurate though as I am unable to find any smd inductors for purchase with this value.

This is good news. Makes me happy to know something is back in business. 😀
I think that 1mH should be fine; also, a wire for the meantime is ok.

Being the same circuit, if you have another dead board with ps2 just take one from there.

Anyway, I'd desolder it and put a wire. My guess is that it broke in 2 separate pieces.
SMDs can crack underneath and look good on the surface.
---

Now it's time for board #2. Open a new thread.