The PB3400c/180 has a 40MHz bus and a 4.5x multiplier to give the 180MHz machine. The 40MHz bus comes from a silver 40MHz crystal (two pins) located at Y1 on the top of the motherboard, with 40.00T5J on it. It is about 2 inches from the front and about an inch left of the battery bay. It is under the battery charging card; you pull the card and it is located about a half inch forwards from the connector. If you replace this crystal with a faster one, the bus, and thus the processor, speeds up.
Robert feels that "The processors need to go through some sort of burning in processor to get up to these speeds, so people need to start out at the lower clock speeds and go up from there. The CPU needs time to adjust to the speed and the possible heat increase. I have gotten mail from people that have jumped straight to 50MHz from the normal 40MHz crystal and telling me that it didn't work. Also there needs to be something about Different CPU's in the different 3400's may all be rated for 300MHz but, that doesn't mean they will all run at the same speed." I'm not so sure about this, but we'll just have to see how things go.
Here is what he has so far:
| Crystal (MHz) | Processor (MHz) | Notes |
|---|---|---|
| 44 | 198 | Everything works |
| 45 | 202.5 | Everything works |
| 47.58 | 214.11 | Everything works |
| 48 | 216 | Everything works |
| 49.375 | 222.1875 | Everything works |
| 49.89 | 224.91 | Everything works |
| 50 | 225 | Everything works |
| 53.33333 | 240 | Too fast, unstable |
| 55 | 247.5 | Too fast, unstable |
Before, and when clock chipped the mach gestalt is 306, and thus we should not expect any software incompatibilities. At 214.11MHz, the MacBench Processor score is 358 while the base 3400c/240 gives just 337. At 222.1875MHz, the MacBinch Processor score is 370 and the FPU score is 324. This is faster than a 240 because of the higher bus speed. Here is a screen dump of several MacBench test results.