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XT Clone Turbo button doing nothing

C

carlos12

Experienced Member
Joined
May 10, 2020
Messages
183
Location
Madrid, Spain
Hi. I have a Turbo XT very similar to the DTK clones. It has a Fujitsu 8088 dual speed, 4.77 Mhz and 10 Mhz. It has a button to switch between slow and fast speed, but the computer always stays on high speed no matter the button is pressed or not. I looked inside but everything looks plugged on it's place. Do you, guys, have any clue about what can be failing?

Just now I can't open the machine, but later I could, so I would post pictures of the inside, if it's helping anyway.

Thanks for your help.
 
Perhaps the switch for turbo fell off the motherboard. Some systems default to turbo when the header/jumper is open and some default to non-turbo.

Sometimes there are key combinations that will change the speed. If it’s a DTK try ctrl-alt-minus
 
On many simple turbo XTs, turbo mode is controlled by pin 13 of the 8284 clock generator chip. When high, the clock signal is taken from pin 14, which is usually connected to the higher-frequency external oscillator. When low, the crystal connected to pins 7 and 16 is used.

When software (key combinations) are used, the input to pin 13 is usually connected to an output of the 8255.

So perhaps this is something to check.
 
I have an XT clone computer that has a turbo switch, but in my case, the turbo switch does nothing because the motherboard has no turbo functionality to switch.
 
From my recollection of the era, the turbo button when I first encountered it worked swell. However, eventually generic cases persisted in maintaining the 'turbo' button long after the turbo button ceased to be directly relevant to the included hardware. So I recall many cases would just have a turbo button that just had no effect.
 
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