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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: rabindranath72 on August 31, 2013, 01:34:18 PM

Title: MTEC Viper 1230/28 RTC: Problems underclocking 68882 FPU?
Post by: rabindranath72 on August 31, 2013, 01:34:18 PM

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

Title: Re: Problems underclocking 68882 FPU?
Post by: GadgetUK on August 31, 2013, 02:54:07 PM

Quote from: rabindranath72;746694

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?

Title: Re: Problems underclocking 68882 FPU?
Post by: rabindranath72 on August 31, 2013, 03:10:18 PM

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. :/

Title: Re: Problems underclocking 68882 FPU?
Post by: Lord Aga on August 31, 2013, 04:16:04 PM

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

Title: Re: Problems underclocking 68882 FPU?
Post by: rabindranath72 on August 31, 2013, 04:53:06 PM

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!

Title: Re: Problems underclocking 68882 FPU?
Post by: ferrellsl on August 31, 2013, 08:02:56 PM

I love happy endings!

Title: Re: Problems underclocking 68882 FPU?
Post by: Djole on August 31, 2013, 09:09:22 PM

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.

Title: Re: Problems underclocking 68882 FPU?
Post by: freqmax on August 31, 2013, 11:10:58 PM

50 millihertz seems awfully slow.. :P

Title: Re: Problems underclocking 68882 FPU?
Post by: rabindranath72 on September 02, 2013, 08:39:07 AM

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.

Title: Re: Problems underclocking 68882 FPU?
Post by: TCMSLP on September 02, 2013, 10:58:29 AM

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!

Title: Re: MTEC Viper 1230/28 RTC: Problems underclocking 68882 FPU?
Post by: Djole on September 02, 2013, 11:23:16 AM

Quote from: rabindranath72;746694

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.