Overclocking A3640

[Sandman]

I am trying to overclock my A3640 for the shear fun of it but I am not having much luck.

I replaced all capacitors on the card and socketed the oscillator.  

I also did the delay line modification as described here: http://members.iinet.net.au/~davem2/overclock/a3640.html

Card works great @ stock 25mhz with both XC68040-25 & XC68040-40 cpus that I tried but won't boot at either 30mhz or 33mhz as is mentioned should be attainable.  

Actually it did boot ONCE at 30mhz but hung-up early on.

A3640 is ver. 3.1 which I am thinking may be the problem.  

Any ideas?

[Sandman]

Yes, I am installing this in an A3000.

I am not sure what speed my zips are but I will check tonight.  I have the A3000 filled with the full 16mb of zips.

I was hoping to at least get this up to 30mhz.  I am planning to heatsink the gal chips and heatsink/fan the '040.

Thanks for the input all!

[Sandman]

Well, I checked my zip's tonight and they are all 70ns.

I also checked my delay line mod and it all looks correct.... I'm totally at a loss at what to try next.

[Sandman]

Actually, I do have a SIMM-to-ZIP adapter that I have never used, I always thought that using the original ZIPs would be faster but I will have to revisit this again.

Do you think that I would have a better o.c. attempt using this with faster than 70ns SIMMS instead?

[Sandman]

I have checked the polarity of all caps on the A3640 and they are all correct.  BTW, they were all just replaced.  

Also checked the +5v on the A3640 @ the caps and it is 5.02v.

The A3000 MB chips are as follows:
Ramsey is -4
SuperBuster -11
SuperDMAC -02
WD -08 (chip was just upgraded from -04)

CPU is XC68040-40 and has a heat-sink and fan.  The GAL's on the A3640 are also heat-sinked.

No zorro cards installed for test, only a CF card through a ACARD scsi-ide and ide-cf adapter.

Still boots fine @25mhz (w/ 50.0 crystal)  but no go with a 60.0 crystal oscillator.

I'm thinking this A3640 just can't do it.  

[Sandman]

Well, I discoved a few things!

With SCSI disconnected, A3000 will boot from floppy @ both 30mhz and 31mhz but will lock up (power and HD leds both stuck on) @ both those speeds with SCSI->CF connected.  Still boots fine to CF @ 25mhz.  

I tried different CF cards and sizes and I get the same results.

I've heard of the A3640 breaking the A3000 SCSI but why only @ overclock speeds?
 
Do I really need a DMAC -04?

[Sandman]

Well, I relplaced the 74F08 @ U103 with a 74HC08 and the machine managed to boot once @ 31mhz but the machine hanged and the graphics corrrupted.  Put back in the 25mhz Oscillator and everything works fine.....

I wish that I didn't have to give up here but I have no idea what else to try.