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Kingston Turbochip 133 (Am5x86). How to change the multiplier?

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First post, by MSxyz

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I've acquired a Kingston Turbochip 133 upgrade module. Basically it's just a small PCB with an Amd 5x86 in PQF package soldered and a couple of voltage regulators. Oh, there's also a small fan glued on top of it (yeah, glued) that gets the power directly for the CPU pins. It was marketed as a cheap plug-in upgrade for motherboards that supported only 5 Volt 486s. Old motherboards simply recognize it as a 486DX or DX2; sometimes even the speed reported by the BIOS is not correct. Cache seems to be locked in WT mode. Any software using CPUID will correctly report it as an Amd 5x86, though.

At any rate, I was wondering if it's possible to set it in 3x mode without heavily modding (ie. using a soldering iron) the PCB. Unless it's under the fan, I've not seen any jumper. Yet, I recall reading of people running those upgrade modules at 150Mhz by adjusting the multiplier. Although it is stable also at 160 MHz, I'd like to test it on a couple of ancient (late '91-early '92) motherboards in place of a 486DX-50. In one case, changing the bus clock is not even an option unless I use a different crystal.

Reply 1 of 5, by akimmet

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I'm fairly certain Kingston intentionally chose WT mode for maximum compatibility.

Many early 486 boards had DMA memory corruption bugs with WB enabled.

I'm fairly certain any multiplier mod would require soldering. There are no jumpers that I recall on my Kingston turbochip.

Reply 2 of 5, by MSxyz

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I agree that the 5x86 is forced to operate in write through mode only for compatibility reasons. Many early chipsets do not support WB for the L1 cache and even when they do, sometimes the motherboard implementation is spotty. I've some 1993-1994 motherboards in which activating write back mode for Cyrix 486s and even for Intel own's DX2, DX4 with WB cache causes random corruption and instability.

As for the multiplier, you confirmed what I feared... I am aware there are other interposers to adapt late 486s to early systems, but the Kingston Turbochip is fairly common and cheap. I cannot say the same for the rest of them.

Reply 3 of 5, by analog_programmer

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Don't the jumpers on the mobo for setting the CPU multiplier work with this POD-like CPU module? AMD 5x86 needs a multiplier setting of x2 to actually work with multiplier of x4.

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Reply 4 of 5, by Horun

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If you cannot use the motherboards jumpers to set multiplier it may be locked with that Kingston, there are 0 ohm resistors on the back that set the cpu type and multiplier IIRC.
You might be able to change them but quick google does not list anything valuable about them.
Yeah they were the cheapest build of those type 486 upgrades with cpu .....

Side note: Back in May 2021, some of us bought some NOS Interposers "CPU Adapter 486SX 486DX Upgrade to DX4 5x86 Systems 3V CPU to 5V Motherboard" without cpu's at ~$18 each, were a great bargain and has jumpers for diff types, multipliers, etc..
Thankfully one member posted about it so the rest interested could grab a few too. Cannot find the post about it now, not that it matters.... but was great member sharing thing at the time 😀

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 5 of 5, by MSxyz

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analog_programmer wrote on 2024-11-09, 08:16:

Don't the jumpers on the mobo for setting the CPU multiplier work with this POD-like CPU module? AMD 5x86 needs a multiplier setting of x2 to actually work with multiplier of x4.

Old motherboards don't have those jumpers. If you've one of those jumpers, chances are you can directly plug an Am5x86.

The Kingston Turbochip was a simple plug-in upgrade that works with pretty much any 486 motherboard.

Horun wrote on 2024-11-10, 04:16:

e: Back in May 2021, some of us bought some NOS Interposers "CPU Adapter 486SX 486DX Upgrade to DX4 5x86 Systems 3V CPU to 5V Motherboard" without cpu's at ~$18 each, were a great bargain and has jumpers for diff types, multipliers, etc.. Thankfully one member posted about it so the rest interested could grab a few too. Cannot find the post about it now, not that it matters.... but was great member sharing thing at the time 😀

Not so long ago, I saw one of those on eBay going for an outrageous price. Just like pretty much anything "vintage" these days...

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