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Disclaimer Use this information at your own risk, don't blame me if you damage your PC card, Risc PC or anything else.
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Hints on de-soldering Try adding solder to each pin before desoldering as solder suckers tend to work better with a large blob of solder rather than a thin film. Similarly, if you only achieve partial desoldering of a pin, add more solder before trying again.
Even after desoldering, each pin may be stuck to one side of the through plated hole and if you try and force the processor out of the board, the through plating will be damaged. To avoid this, flick each pin with the soldering iron to release it from the plating. N.B. the soldering iron should only be in contact with the pin for a very brief period, just enough to break the pin away from the plating. If it is left in contact with the pin, the remaining solder may melt and attach the pin back to the plating.
Before attempting to lift the processor out of the pcb, make sure that each pin is free and then the processor can be removed without force.
After extracting the processor, remove any excess solder and straighten any bent pins, solder a 168 or 169 pin PGA socket into the pcb and plug the processor back into the socket. The PC card should then be tried in a RISC PC to ensure that the desoldering hasn't damaged anything.
If you already have a processor, you will need a voltage adapter card and heatsink/fan. Watford electronics do a DX4 adapter card claimed to be suitable for AMD 486DX4-100 and Cyrix 586-100 for 29 pounds plus VAT and a 486 heatsink/fan for 9 pounds plus VAT. Note that I have only tried the Powerleap 586/133 upgrade kit so I don't know if the above adapter will work. Also, if the processor doesn't support writeback cache then it might not be worth upgrading as write through cache slows the processor down. (See benchmarks below).
The three surface mount links are LK4 (3 pin), LK5 (2 pin) and LK8 (2 pin) on the processor side of the card all along one edge of the CPU.
With the TI 486SXL the links are as follows:-
Finally, the 66MHz clock generator must be modified to supply a 33Mhz clock to the processor with the addition of two TTL ICs:-
These two must be 'F' type TTL chips and should be connected together as shown in the circuit diagram with 0v connected to pin 7 and +5v to pin 14 of both ICs. You should also connect 0.01uF decoupling capacitors to pins 7 and 14 of each IC.
Locate the 66Mhz oscillator module X1. On the other side of the PCB under this module, locate and remove R25. Connect the 66Mhz crystal side of the R25 pad to the input of the clock divider and the other side to the output of the divider.
+5v and 0v for the two TTL chips can be picked up from two pins on the crystal module (top left = 0v, bottom right = +5v)
The processor RESET line on pin C16 of the processor must be connected to the above clock circuit. See the pinout drawing for the position of C16 on the processor.
The circuit ensures that the 33mhz clock is high immediately after a reset (the TI 486SXL does this internally).
Surface mount versions of the above ICs are preferable and they should be glued to the PCB near the crystal pinouts (making sure that their pins don't touch any circuitry). It is also worth adding a link to select either the new 33Mhz clock or the original 66 Mhz clock. Changing this link and the other links mentioned above would allow the original TI 486SXL to be plugged back into the board for benchmark comparisons etc.
Finally, the processor should be configured for writeback operation. With the AMD 5x86, this is achieved by connecting the WB/!WT line on B13 of the processor to VCC. On the Powerleap 586/133 upgrade, this is done by a dip switch on the voltage adapter card. If you are using an AMD 5x86 with a different voltage adapter, you may need to solder a 4.7k resistor from B13 (WB/!WT) to B11 (VCC) (See the pinout drawing for pin locations). (Make sure that B13 is not connected to anything else on the voltage adapter).
Note that with the Cyrix 586 processor, writeback/writethrough configuration is done entirely by software.
i.e. delete any directory or module called PCSLEEP in the following path:
$.!Boot.Choices.Boot.PreDesk
After deleting, power down and restart the RISC PC.
The !PC control software should be configured as follows :-
If you add /MACHINE:AT to the HIMEM.SYS line of your CONFIG.SYS file it will force correct operation.
i.e.
DEVICE=C:\DOS\HIMEM.SYS /MACHINE:AT
DEVICE=C:\WINDOWS\HIMEM.SYS /MACHINE:AT
NORTON SI LANDMARK DUKE NUKEM 3D TI 486 SXL 23 78 3 fps AMD 5x86 WT 23 78 8 fps AMD 5x86 WB 285 441 10 fpsAs you can see, the benchmark programs don't show any speed improvement until level 1 writeback is enabled whereas a 'real' program shows progressive improvement. (This demonstrates why it isn't worth upgrading a gemini 1 based card with the earlier DX2 and DX4 processors which were writethrough only).
I have run DOS 6.22, Windows 3.11, Windows 95 and various games including Doom, Duke Nukem 3D, and even Quake, without any problems so far.