A3000 speed limit

toddbailey · 11 August 2015, 07:29

just how fast can you over clock a stock a3000 ? while it comes in 16 or 25 mhz flavors, how fast can it go assuming the cpu is not an issue?

alexh · 11 August 2015, 09:15

AFAIK it is 25MHz. You can't overclock the onboard CPU beyond 25 MHz because the clocks and the dividers which go to the Amiga chipset are only for 32MHz and 50MHz crystals. You can't over clock the Amiga chip set/bus and get good results.

AFAIK you can set the clock divided for the memory independently of the Amiga bus so if you can find 50ns ZIP ram you can run your RAM at 2x speed. This is well documented.

The FPU can also be independently overclocked. But imo why bother. Nothing uses the FPU.

If you want to over clock you need accelerator board

SpeedGeek · 11 August 2015, 14:47

Overclocking the A3000 is always a case of "Your Mileage Will Vary". But most A3000s can manage 30MHz with Fast RAM (at least 70ns) and timing mods (e.g. CLK90, replacing the 74F08 with 74AC08).

Beyond that, SDMAC will begin to lock up and you risk overheating the SMD 030. But you can still overclock the FPU past 30MHz with cut and jumper mods (if it's the 68882 up to 50MHz).

Good luck!

P.S. There are 2 versions of SDMAC (02 & 04). Most have the 02 version and only a very few have the 04 version (usually A3000Ts). The 04 version may have some timing improvements which help with overclocking (but unfortunately it's not been confirmed yet).

toddbailey · 12 August 2015, 03:33

Quote:

Originally Posted by SpeedGeek

Overclocking the A3000 is always a case of "Your Mileage Will Vary". But most A3000s can manage 30MHz with with Fast RAM (at least 70ns) and timing mods (e.g. CLK90, replacing the 74F08 with 74AC08).

Beyond that, SDMAC will begin to lock up and you risk overheating the SMD 030. But you can still overclock the FPU past 30MHz with cut and jumper mods (if it's the 68882 up to 50MHz).

Good luck!

P.S. There are 2 versions of SDMAC (02 & 04). Most have the 02 version and only a very few have the 04 version (usually A3000Ts). The 04 version may have some timing improvements which help with overclocking (but unfortunately it's not been confirmed yet).

yeah, fans and heat sinks are all part of the project, I also plan to replace the 16 meg processor with a chip rated for higher speeds, I can get a 33 meg chip for about $15 bucks off ebay. but I'll also need a smd type soldering station. considering the cost of the custom chips and their availability, not a bad idea to use stick on heat sinks.

bebek · 13 August 2015, 17:35

Igot my stock at 33MHz but SCSI does not work then. It does not bother me as I do not use it. CPU is not much warmer than stock. No other IC's were upgraded.

Ze_ro · 29 September 2015, 05:35

For whatever it might be worth, I have an older 16MHz model, and successfully "overclocked" it to 25MHz. I put some cheap RAM heatsinks on the CPU just in case, but it doesn't even seem to get particularly hot. It's been 100% stable like this... it hasn't locked up or rebooted or anything like that.

I actually HAD to overclock it in order to overcome some Zorro related problems.

--Zero

tnt23 · 03 November 2015, 15:59

Quote:

Originally Posted by SpeedGeek

P.S. There are 2 versions of SDMAC (02 & 04). Most have the 02 version and only a very few have the 04 version (usually A3000Ts). The 04 version may have some timing improvements which help with overclocking (but unfortunately it's not been confirmed yet).

If overclocking is not the main goal, is the SDMAC-04 really needed to overcome SCSI problems with A3640?

SpeedGeek · 03 November 2015, 19:33

No, not really. I think SDMAC 04 was really over-rated in it's ability to solve timing problems primarily caused by Ramsey's over-dependence on CLK90. I think C= was also looking for a way fix timing problems with the A3000T (they really messed up the clock circuit for the A3000T).

SDMAC 04 chips are VERY RARE and VERY EXPENSIVE so I would look for other solutions before trying to find one.

tnt23 · 06 November 2015, 20:12

I have had a closer look at my A3640 and it turned out that it had been upgraded from v3.0 to v3.2, however I don't see any 'cut and jumper' fix on U200 chip. There obviously had been some soldering done, probably the fix had been removed.

Somehow the board was working pretty stable (apart from SCSI issues). I have made cut and jumper fix again, does not seem to make any difference.

The board was said to be prepared for overclocking. Apart from socketed rezonator, there is a delay fix (5ns instead of 10ns). Could this lead to issues if 040 is still running at 25MHz? Should I try to restore 10ns tapping?

SpeedGeek · 07 November 2015, 14:27

An upgraded Rev. 3.0 A3640 is another serious case of "Your Mileage Will Vary" but you should do the U200 cut and jumper mod as part of the 3.2 upgrade. This is needed to fix the STERM sampling bug.

Also, don't forget these A3640's are notorious for electrolytic cap problems.

If modified CLK90 timing didn't solve your SCSI problems then you probably don't have SCSI DMA transfer errors. You most likely have SCSI Target to Host transfer errors.

Check your WD SCSI chip Rev. (Stock A3000's shipped with Rev. 4 but most A3000 users have already upgraded to Rev. 8 or the AMD version).

Also, check your SCSI bus termination, SCSI cabling and set your SCSI Prefs to ASYNCH mode since some SCSI targets are buggy in SYNCH mode.

tnt23 · 07 November 2015, 20:09

@SpeedGeek, thanks for your reply.

Quote:

Originally Posted by SpeedGeek

An upgraded Rev. 3.0 A3640 is another serious case of "Your Mileage Will Vary" but you should do the U200 cut and jumper mod as part of the 3.2 upgrade. This is needed to fix the STERM sampling bug.

I made the cut'n'jumper mod but did not feel any difference since.

I have then decided to restore 10ns tap, and this seems to positively impact things. No more errors reported by SCSI tester (http://aminet.net/package/driver/media/stest20).

Quote:

Also, don't forget these A3640's are notorious for electrolytic cap problems

Previous board owner already took care of them by replacing caps with new ones.

Quote:

If modified CLK90 timing didn't solve your SCSI problems then you probably don't have SCSI DMA transfer errors. You most likely have SCSI Target to Host transfer errors.

Well, after I restored original 10ns tap connection, checksum errors became quite rare. Better than it had been before, but they still pop up once in a while.

Quote:

Check your WD SCSI chip Rev. (Stock A3000's shipped with Rev. 4 but most A3000 users have already upgraded to Rev. 8 or the AMD version).

Mine is PROTO WD33C93A-PL 00-04. AMD replacement ordered, expect it to arrive any time soon. I was under impression it could help with removable media, but still worth trying anyway.

Quote:

Also, check your SCSI bus termination, SCSI cabling and set your SCSI Prefs to ASYNCH mode since some SCSI targets are buggy in SYNCH mode.

Resistor packs installed on the mobo, infamous diode checked, TERMPWR measured as +4.5V. Cable itself is 20cm in length, with good connectors. On the disk side (SCSI2SD emulator), termination is also installed.

I am pretty positive I have ASYNC set in SCSI Prefs, but will check.

quantum8 · 11 July 2020, 01:20

Quote:

Originally Posted by SpeedGeek

Overclocking the A3000 is always a case of "Your Mileage Will Vary". But most A3000s can manage 30MHz with Fast RAM (at least 70ns) and timing mods (e.g. CLK90, replacing the 74F08 with 74AC08).

Sorry to bring up an old thread, but just wondering what the CLK90 and 74* timing mods are and if there's any links or further explanations on it?

SpeedGeek · 11 July 2020, 20:48

Quote:

Originally Posted by quantum8

Sorry to bring up an old thread, but just wondering what the CLK90 and 74* timing mods are and if there's any links or further explanations on it?

The only link is the A3000 schematic. The rest you will have to figure out for yourself:

https://www.amigawiki.org/doku.php?i...ice:schematics

hammer · 13 September 2020, 05:01

Quote:

Originally Posted by alexh

AFAIK it is 25MHz. You can't overclock the onboard CPU beyond 25 MHz because the clocks and the dividers which go to the Amiga chipset are only for 32MHz and 50MHz crystals. You can't over clock the Amiga chip set/bus and get good results.

AFAIK you can set the clock divided for the memory independently of the Amiga bus so if you can find 50ns ZIP ram you can run your RAM at 2x speed. This is well documented.

The FPU can also be independently overclocked. But imo why bother. Nothing uses the FPU.

If you want to over clock you need accelerator board

TFX (warplanes simulation) uses the FPU.

11 August 2015, 07:29	#1
toddbailey Registered User Join Date: Jul 2014 Location: carnation / usa Posts: 71	A3000 speed limit just how fast can you over clock a stock a3000 ? while it comes in 16 or 25 mhz flavors, how fast can it go assuming the cpu is not an issue?

11 August 2015, 14:47	#3
SpeedGeek Moderator Join Date: Dec 2010 Location: Wisconsin USA Age: 60 Posts: 839	Overclocking the A3000 is always a case of "Your Mileage Will Vary". But most A3000s can manage 30MHz with Fast RAM (at least 70ns) and timing mods (e.g. CLK90, replacing the 74F08 with 74AC08). Beyond that, SDMAC will begin to lock up and you risk overheating the SMD 030. But you can still overclock the FPU past 30MHz with cut and jumper mods (if it's the 68882 up to 50MHz). Good luck! P.S. There are 2 versions of SDMAC (02 & 04). Most have the 02 version and only a very few have the 04 version (usually A3000Ts). The 04 version may have some timing improvements which help with overclocking (but unfortunately it's not been confirmed yet). Last edited by SpeedGeek; 12 August 2015 at 14:53.

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11 August 2015, 09:15	#2
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,331	AFAIK it is 25MHz. You can't overclock the onboard CPU beyond 25 MHz because the clocks and the dividers which go to the Amiga chipset are only for 32MHz and 50MHz crystals. You can't over clock the Amiga chip set/bus and get good results. AFAIK you can set the clock divided for the memory independently of the Amiga bus so if you can find 50ns ZIP ram you can run your RAM at 2x speed. This is well documented. The FPU can also be independently overclocked. But imo why bother. Nothing uses the FPU. If you want to over clock you need accelerator board

13 August 2015, 17:35	#5
bebek Registered User Join Date: Dec 2009 Location: Poole UK Posts: 349	Igot my stock at 33MHz but SCSI does not work then. It does not bother me as I do not use it. CPU is not much warmer than stock. No other IC's were upgraded.

29 September 2015, 05:35	#6
Ze_ro Registered User Join Date: Apr 2006 Location: Winnipeg / Canada Posts: 50	For whatever it might be worth, I have an older 16MHz model, and successfully "overclocked" it to 25MHz. I put some cheap RAM heatsinks on the CPU just in case, but it doesn't even seem to get particularly hot. It's been 100% stable like this... it hasn't locked up or rebooted or anything like that. I actually HAD to overclock it in order to overcome some Zorro related problems. --Zero

03 November 2015, 19:33	#8
SpeedGeek Moderator Join Date: Dec 2010 Location: Wisconsin USA Age: 60 Posts: 839	No, not really. I think SDMAC 04 was really over-rated in it's ability to solve timing problems primarily caused by Ramsey's over-dependence on CLK90. I think C= was also looking for a way fix timing problems with the A3000T (they really messed up the clock circuit for the A3000T). SDMAC 04 chips are VERY RARE and VERY EXPENSIVE so I would look for other solutions before trying to find one.

06 November 2015, 20:12	#9
tnt23 Registered User Join Date: Feb 2008 Location: Saint-Petersburg / Russia Posts: 324	I have had a closer look at my A3640 and it turned out that it had been upgraded from v3.0 to v3.2, however I don't see any 'cut and jumper' fix on U200 chip. There obviously had been some soldering done, probably the fix had been removed. Somehow the board was working pretty stable (apart from SCSI issues). I have made cut and jumper fix again, does not seem to make any difference. The board was said to be prepared for overclocking. Apart from socketed rezonator, there is a delay fix (5ns instead of 10ns). Could this lead to issues if 040 is still running at 25MHz? Should I try to restore 10ns tapping?

07 November 2015, 14:27	#10
SpeedGeek Moderator Join Date: Dec 2010 Location: Wisconsin USA Age: 60 Posts: 839	An upgraded Rev. 3.0 A3640 is another serious case of "Your Mileage Will Vary" but you should do the U200 cut and jumper mod as part of the 3.2 upgrade. This is needed to fix the STERM sampling bug. Also, don't forget these A3640's are notorious for electrolytic cap problems. If modified CLK90 timing didn't solve your SCSI problems then you probably don't have SCSI DMA transfer errors. You most likely have SCSI Target to Host transfer errors. Check your WD SCSI chip Rev. (Stock A3000's shipped with Rev. 4 but most A3000 users have already upgraded to Rev. 8 or the AMD version). Also, check your SCSI bus termination, SCSI cabling and set your SCSI Prefs to ASYNCH mode since some SCSI targets are buggy in SYNCH mode.

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