If the fuse tests good I would say there is probably a good chance the keyboard controller would fix it.

kingcake wrote on 2024-04-14, 21:25:

If the fuse tests good I would say there is probably a good chance the keyboard controller would fix it.

Thanks! Ordered a knockoff from Aliexpress... We'll see if they are any good.

kingcake wrote on 2024-04-14, 21:25:

If the fuse tests good I would say there is probably a good chance the keyboard controller would fix it.

Darn it... After changing the HT6542B chip (which was a legit Holtek) and the RTC while I was at it; same problem. Anyone has an idea of else I should be checking?

Since you said that you've tested everything, then what did you exactly measure?

The circut of the 6542b is not complecated.

First, did you measure the VDD? What's the value?

As long as you connect a keyboard, measure the two pull-up resistors on pin 37 and 38, and of course you'd better use the oscilloscope and check the waveform. Since these two pins are clock and data pin to the keyboard.

Now we change to the input, those are pin 6, 8 and 10. Also, use oscilloscope and check the waveform.

The chip's application principle is simple, the data comes from the CPU to the chip ( input ), then sent to the keyboard ( output ).
BTW, the input signal looks like the SPI signal, and the out is like the I2C.

The method of testing is also simple, first make sure the power supply ( vdd ) is ok, the check the output and input signal.

Of course maybe you have to check the oscillator, but I highly doubt that.

Please show us the measuring result, then we analzy the fault。

BTW, just curious, why did you replace the chip at the beginning? Was it so hot? I mean rediculously hot? What made you think this chip was broken?

After messing around with the PS2 mouse pins, I would replace the two external inverters at pins 23 and 24 first.
They are probably part of some 14-pin DIP circuit between the ISA slots or some SOP package near the KBC.

quigonhu wrote on 2024-05-09, 10:47:

Since you said that you've tested everything, then what did you exactly measure? […]
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Since you said that you've tested everything, then what did you exactly measure?

6542b.JPG

The circut of the 6542b is not complecated.

First, did you measure the VDD? What's the value?

As long as you connect a keyboard, measure the two pull-up resistors on pin 37 and 38, and of course you'd better use the oscilloscope and check the waveform. Since these two pins are clock and data pin to the keyboard.

Now we change to the input, those are pin 6, 8 and 10. Also, use oscilloscope and check the waveform.

The chip's application principle is simple, the data comes from the CPU to the chip ( input ), then sent to the keyboard ( output ).
BTW, the input signal looks like the SPI signal, and the out is like the I2C.

The method of testing is also simple, first make sure the power supply ( vdd ) is ok, the check the output and input signal.

Of course maybe you have to check the oscillator, but I highly doubt that.

Please show us the measuring result, then we analzy the fault。

BTW, just curious, why did you replace the chip at the beginning? Was it so hot? I mean rediculously hot? What made you think this chip was broken?

Thanks the tips!

The only reading I've done were for continuity around the PS/2 (keyboard and mouse) connectors... They were all fine, so I assumed it was the chip. I based my actions on previous posts on the forum... I should have checked the output like you mentioned...

majestyk wrote on 2024-05-09, 11:33:

After messing around with the PS2 mouse pins, I would replace the two external inverters at pins 23 and 24 first.
They are probably part of some 14-pin DIP circuit between the ISA slots or some SOP package near the KBC.

This is the board I have:

Are you referring to the small ones North and North East of the HT chip or the larger one between the top 2 ISA slots?