As an FYI
My Tandy 1000rlx -10mhz 286 has a 40mhz crystal

Would need to know more about the board to comment on what might be happening

Thanks! I can take a photo of it. It's definately a 20mhz CPU and all the chipset chips say 20mhz on. Will try to upload one tomorrow 😀

I think it's entirely possible that turbo switches between 10 and 20MHz. My permanent 286 toggles between 8 and 20, my 286 test board between 6 and 12.

I'd probably be bold enough to experiment with anything that looks like a jumper header. On the fly, running a real time benchmark like topbench or landmark. Landmark2.0 even beeps intermittently while running which is a royal pain but useful in this case - you don't even have to look, just listen to the (hopefully) changing pitch...

Does this look like your board ? http://www.win3x.org/uh19/motherboard/show/6772

Thanks everyone for your help!
I've taken a few pics. It's similar to the one linked above, but not quite the same. I've fiddled with a few of the more encouraging looking jumpers, nothing I've tried alters the speed but without any kind of manual or layout drawing it's hard to know what to look for. I've not found one for this board online.

Some 286 systems had the turbo control actually operated by keyboard shortcut and not a jumper. It's possible that yours may be one of them.

I've got a few 286 boards and none of them are keyboard-shortcut-only, but one of them can be jumpered for front-panel button or keyboard shortcut, and in keyboard mode my modern PS/2 keyboard doesn't activate it at all.

BTW, you're going to remove/replace or thoroughly clean that keyboard socket, right?

megatron-uk wrote on 2021-03-15, 09:38:

BTW, you're going to remove/replace or thoroughly clean that keyboard socket, right?

I will if I can get it to go faster than my slide rule 🤣

I did try using a keyboard with the ctrl+alt+num+ etc but it didn't do anything. The manual for the other Neat 286 boards I've found on the Internet all have a turbo pin header so I assume this one does too, but no idea where it is or whether it starts in high or low speed. I assume it's the latter, and to be honest it's slow even for a 10mhz 286 let alone a 20mhz.

I don't know much about the clock timer settings either, they look right to me but I'm not confident! I don't know my CLK2IN's from my SCLK/2's...

Just going by the pins...

JP15 5pin pwr led & keylock
JP14 4 pin speaker
JP13 2pin JP12 2pin JP11 2pin JP10 2pin no idea, but there should be turbo button, turbo led, reset button & ... ?
JP3, JP? JP4, JP5, JP?, JP9, JP? mostly no idea, though JP9 might be selecting between SIP and DIP memory.

Can you make a setting in your BIOS?

Otherwise I am afraid you need to try. It should be one of the JP10-JP15.
The 5-Pin is usually for Keylock.
One of the 4-Pin is for the speaker - you should figure out this one first. Connect Pin 1 and 4 to the speaker and listen if you hear a beep after powering on...
2 of the remaining ones should be reset + turbo.

weedeewee was 1st 😀
Yes, also turbo-LED and power-LED should be one of the remaining. You should also test this before trying to short the turbo-switch...

Some good news and some less good news!

The good news is I experimented with some leds and jumpers and can now say that JP11 is reset, JP12 is the Turbo LED and JP10 is the turbo switch.

Shorting JP10 does indeed double the speed, and Norton now correctly states that it's a 20mhz chip rather than 10mhz. So that's good! And the chip is actually getting warm to the touch now, it remained stone cold before.

However, it's still benchmarking almost exactly the same as a 286-12, and well behind my 286-16. Something is amiss.

Any ideas? Chipset timings or something? Thanks so much!

Mouldotron wrote on 2021-03-15, 13:53:

However, it's still benchmarking almost exactly the same as a 286-12, and well behind my 286-16. Something is amiss.

Any ideas? Chipset timings or something? Thanks so much!

Bios wait states / bios shadow rom / cacheing ...

What are the Norton results at 20MHz?

It's getting a score of 9.0 at present, would have expected more like 16?

did you verify the bios settings as per my previous comment ?

Yep, I'd say around 15-16 for a healthy 20MHz board running at 0-ws.

Looking at my benchmarks, I'd say a score of ~9 more closely mirrors a 16MHz processor running with 1-ws.

Thanks 😀
Yes I've been into the Extended Cmos, and have taken these two screenshots. What do you think?

enable the main & video bios shadow. and add another 2 meg of ram if you can. actually having interleaved banks also helps a smidge.