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Jetway J-402B 3/486 motherboard - reversed turbo switch/LED functionality

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First post, by jesolo

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I have this motherboard: https://theretroweb.com/motherboards/s/jetway-j-402b.
Unfortunately, the BIOS ROM on my motherboard became corrupted and I was lucky enough to obtain another one from a fellow user here on Vogons (this is also the version that was uploaded to the Retroweb) - https://theretroweb.com/motherboard/bios/jetw … 3f929780407.zip

The motherboard is working fine now but, I have the following issue (and I don't recall having this issue prior to the original BIOS becoming corrupt):
The motherboard has both a 2-pin header for a turbo LED and a 2-pin header for a turbo switch.
When I short the turbo switch (provided that I connect the turbo LED the right way around), the LED light comes on (in other words, it will generate a 5V signal to the LED pin when the turbo switch header is shorted - this has been confirmed with my multimeter as well).
Unfortunately, when the turbo switch header is shorted, the PC actually runs in non-turbo (normal) mode. Obviously, I want the turbo LED to come on when the PC is running in turbo mode.
I've tried setting the system boot up speed to high in the CMOS setup, switching the connectors around but, there was no change.

Please note that, in order to understand how the motherboard functions and in which circumstances it will turn on the turbo LED, I actually bypassed the turbo switch in the PC case and shorted the 2-pin turbo header directly with a jumper.

I tried looking for a MR BIOS replacement but, I wasn't able to find a version that would work properly on my motherboard. The closest one I could track down was OPTI4BH but, the turbo switch has no impact when I push the switch or short the header (Ctrl+Alt++ & Ctrl+Alt+- does work but, the LED just remains on, which is not what I want).

Does the above something to do with the BIOS on the motherboard?

If that is the case, can one control how the turbo functionality operates on the motherboard via the BIOS so that, instead of the PC running in normal mode when the turbo switch header is shorted it actually runs in turbo mode when the turbo switch header is shorted? Would it be possible then to re-program the current BIOS revision to "tell" the motherboard to put the PC in turbo mode when the turbo header is shorted?

Reply 1 of 4, by bogdanpaulb

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Hardware solution: check at the tb led connector, and depending of what type of driver conf the board uses for that led this could work (can't damage anything if you don't mess with anything else!), you should have 2 pins. One has the signal for the led and one should be ground or 5v. Depending on what you have on the second pin, switch it (if you have ground use 5v instead, if you have 5v use ground instead) by switching i mean connect the pin of that led somewhere else and reverse the polarity of the led also (you may need to ad a resistor in series with the led if it's to bright).

Solution 2: use a transistor to invert the signal.

Do this only if you have some electronics knowledge.

Reply 2 of 4, by jesolo

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bogdanpaulb wrote on 2023-04-11, 19:50:

Hardware solution: check at the tb led connector, and depending of what type of driver conf the board uses for that led this could work (can't damage anything if you don't mess with anything else!), you should have 2 pins. One has the signal for the led and one should be ground or 5v. Depending on what you have on the second pin, switch it (if you have ground use 5v instead, if you have 5v use ground instead) by switching i mean connect the pin of that led somewhere else and reverse the polarity of the led also (you may need to ad a resistor in series with the led if it's to bright).

Solution 2: use a transistor to invert the signal.

Do this only if you have some electronics knowledge.

Don't quite follow. The motherboard only outputs 5V to the one pin of the LED connector on the motherboard when the two pins of the turbo switch is shorted. That also places the motherboard in "normal" speed mode. I don't see how connecting the LED in any other way is going to reverse this.

I don't necessarily want to make changes to the switches and connectors coming from the case.

I'm just wondering whether this symptom of the motherboard could have something to do with the BIOS itself and whether a BIOS tweak could effectively reverse how the motherboard behaves when the turbo header is shorted (in other words, I want the motherboard to run in turbo mode when the two pins of the turbo switch are shorted).

Reply 3 of 4, by bogdanpaulb

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I'm talking about something like this: http://sullystationtechnologies.com/npninverter.html .
I'm saying this because, if i remember correctly some old motherboards had the 'turbo led' signal inverted from the factory so they could work with a speed display.

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Reply 4 of 4, by jesolo

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bogdanpaulb wrote on 2023-04-12, 00:01:

I'm talking about something like this: http://sullystationtechnologies.com/npninverter.html .
I'm saying this because, if i remember correctly some old motherboards had the 'turbo led' signal inverted from the factory so they could work with a speed display.

Ok, thanks. Let me do some further digging

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