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View Full Version : Repairing a Cyrix CPU which "almost" works on a Pentium board



Rauli
July 20th, 2014, 01:05 AM
I have 3 Socket 7 boards (for classic & MMX Pentiums, and clones) which work. I acquired a Pentium clone (a Cyrix 6x86) but I noticed that the 4 soldered resistors or capacitors on top of the CPU are partially or completely scratched. I tried it on 2 of the boards and they didn't run at all, so I thought it was fried. But before throwing away the CPU I tried it on the 3rd board and, surprisingly, it boots, it passes the POST and I can even enter SETUP and navigate all the screens and options. But it fails booting the O.S. (DOS) from hard disk or floppy.

Anyway, if it passes the POST and runs the SETUP, the CPU must not be very damaged. Maybe I just need to replace the top resistors. But I need to know the values, and what exactly they are (resistors, capacitors, fuses...) I can't find this information on Cyrix datasheets, on some of them there's something about "internal pull-up resistors", but I don't know if they mean the resistors built on the top, and anyway they don't mention the resistor values.

So, does anybody know which components are they, and their values?

I mean the 4 components mounted on top of the CPU which can be seen in this photo (http://www.cpu-info.com/img/cpu/6x86/Cyrix6x86-P133-33vor352vL.jpg) (that's like my CPU, but with components in good shape)

Chuck(G)
July 20th, 2014, 08:11 AM
I can tell you that those are capacitors, not resistors. I can't tell you their values as my collection of these does not include chips with capacitors on the top--they're the "L" versions of the chip.

Rauli
July 20th, 2014, 12:07 PM
I can tell you that those are capacitors, not resistors.

And, for my curiosity, what's the way to distinguish them? The colour? Are resistors always black? Or maybe you have some document which I lack...

Chuck(G)
July 20th, 2014, 02:16 PM
Well, take a look at them--they're wider than they are long--if these were resistors, the contacts would be on the other two sides.

...and consult this page (http://www.cpu-collection.de/?l0=co&l1=Cyrix&l2=6x86) or search on "6x86 capacitors".

Rauli
July 22nd, 2014, 12:51 PM
OK, they should be fixable once their valures are known... BTW, it's not the 1st one I have seen with manipulated capacitors. What was the purpose? Overclocking?

Chuck(G)
July 22nd, 2014, 01:05 PM
Depends upon the value. It could have been simple bypassing, given the complexity of the chip.