MTEC Viper 1230/28 RTC: Problems underclocking 68882 FPU?

[rabindranath72]

Hi all,
I recently acquired an MTEC 1230/28 RTC without coprocessor. I bought one yesterday, PLCC package, 40MHz. I plugged the coprocessor trying 14MHz and 28 MHz configurations, but the Amiga 1200 won't even boot. From what I can understand, there is no need for an oscillator clock if one goes by one of those frequencies, so is it possible that the 40MHz FPU doesn't like being underclocked? Do I need a 40 MHz oscillator?

Thanks,
Antonio

[GadgetUK]

Hi all,
I recently acquired an MTEC 1230/28 RTC without coprocessor. I bought one yesterday, PLCC package, 40MHz. I plugged the coprocessor trying 14MHz and 28 MHz configurations, but the Amiga 1200 won't even boot. From what I can understand, there is no need for an oscillator clock if one goes by one of those frequencies, so is it possible that the 40MHz FPU doesn't like being underclocked? Do I need a 40 MHz oscillator?
 
Thanks,
Antonio

I wouldnt think so?  Is the chip in the right way around - pin 1 aligned up with the notch etc?  Is it possible there's also a jumper you need to plug as well?   Some expansions also have a seperate crystal socket for the coprocessor - is it possible your board has that socket and its empty?

[rabindranath72]

Yes the chip is correctly inserted. The board has three jumpers, one for 14MHz, one for 28MHz and another for async clock. There is a socket for an oscillator, but looking at the manual it seems it's for asyncronous clocking. So I'd say you need an oscillator only for frequencies which are not 14MHz and 28MHz. If that's the case, either the processor won't be downclocked, or it's broken. :/

[Lord Aga]

Well, what happens when you put it in async position ?

[rabindranath72]

Apparently the FPU wasn't seated well. I removed it, and placed it again, and it works. Duh! :laughing: I suppose I could buy a crystal oscillator and take advantage of the full speed of the coprocessor.

Thanks everybody!

[ferrellsl]

I love happy endings!

[Djole]

I have the same accelerator and a 50mhz crystal in async mode. It would be more useful if we could overclock the cpu to 50mhz.

[freqmax]

50 millihertz seems awfully slow..

[rabindranath72]

That's what happened: the processor came within a plastic sleeve, closed on two sides with sticky tape. Apparently some residue from the tape had stuck on some of the processor's pins, so it acted as insulation.

[TCMSLP]

I've given up with FPUs.  I've tried two (one second hand, one brand new in unopened packaging) and both cause my accelerator to fail to boot.   My accelerator (68030) is clocked at 50MHz and the FPUs are 40MHz parts but I believe they should overclock fine.

I'm happy to hear you've had more success!

[Djole]

Hi all,
I recently acquired an MTEC 1230/28 RTC without coprocessor. I bought one yesterday, PLCC package, 40MHz. I plugged the coprocessor trying 14MHz and 28 MHz configurations, but the Amiga 1200 won't even boot. From what I can understand, there is no need for an oscillator clock if one goes by one of those frequencies, so is it possible that the 40MHz FPU doesn't like being underclocked? Do I need a 40 MHz oscillator?

Thanks,
Antonio

Do you have 4 or 8mb in it ? I just have 4, would like to get 8... somewhere.