Pushing the Apple PowerPC 601 upgrade card to 80MHz (in 40MHz Quadra 800)?

[willmurray461]

I have an Apple PowerPC 601 upgrade card that I want to run at 80MHz in my overclocked 40MHz Quadra 800. I replaced the 66MHz QFP 601 with an 80MHz rated part. However, the computer won't boot at 80MHz (crashes immediately upon loading from the hard disk). It at least chimes and shows video though.

When tested in a 33MHz machine, the card works without issue.

I'm thinking about replacing the Cache SRAMs (and maybe even the ROMs) with faster rated parts.

However, before I do so, does anyone know if there's some limitation of the PDS slot that prevents it from being stable at 40MHz no matter what? Or is it theoretically possible to get the card to work as long as I use faster parts?

 

[cy384]

There are some notes here http://www.applefool.com/clockchipping/wombat.html

 

[Franklinstein]

Interesting question. LEM's guide doesn't mention the only 40MHz Mac, the Quadra 840av, as being compatible with the PPC Upgrade Card, so maybe a 40MHz bus upsets it (beyond the obvious overclocking of the CPU). Apparently the official Apple version of the card doubles the host machine's bus base clock to set the card's CPU clock, so you can't just swap crystals around on the card. It could be worthwhile finding a Daystar or Sonnet part instead, since those seem to use fixed multipliers and decouple the card's CPU from the host machine's bus clock.

 

[aladds]

I'd guess that the architectural differences in the 840av (DSPs, Geoport stuff) would be a bigger reason that the 601 card wouldn't work.

 

[Franklinstein]

The PowerPC Upgrade Card works in a Quadra 660av, which has a lot of the same features of the 840av including the DSP.

 

[Bolle]

Simple reason for that… the 840AV doesn’t have PDS.

 

[jeremywork]

The Sonnet/Daystar 100MHz version doesn't decouple from the host's bus clock, it switches from a 4x multiplier to a 3x multiplier to allow for use in 25MHz and 33MHz hosts. The 80MHz model with 72-pin SIMMs does have it's own decoupled clock, but apparently is nearly intolerant of clock adjustments.

FWIW I have both an Apple 2x version and a Sonnet/Daystar 3-4x version in Q950s with NewerTech PowerPumps, and with each card the machines only clock up to about 38.5MHz before becoming unstable (77.1MHz and 115.6MHz, respectively.) When running off the 040, 45MHz+ is stable.

Some anecdotes suggest these cards can remain stable at faster speeds with the 040 physically removed, which I haven't tried. Also possible the PowerPump's clock is noisier than a direct oscillator swap.

There is this LEM page with some data:

Overclocking the PowerPro PPC Upgrade | Low End Mac

 

[willmurray461]

After some more fiddling around, it looks like the issue definitely is related to component speed ratings. When cold, the machine actually boots all the way to the desktop. However, as the computer warms up, small graphical glitches start to occur and a few minutes later the machine completely hangs.

I'm hoping the problems are coming from the card, not the motherboard.

As far as I can tell, the only culprits should be the CPU, the SRAM, the ROMS, or the VLSI ASIC. Hopefully the limiting factor is not the VLSI ASIC, since it's the only part that can't be replaced.

Funnily enough, you can still order the SRAM chips brand new from Mouser. I ordered a set of 10ns variants (the originals were 15 and 17ns). Hopefully they will solve the issue. You can replace the ROMS with 29F800's or similar, but I think you'll have to lift a few legs of the chip since flash chips have a slightly different pinout.

On a related note, has anyone ever seen evidence of fake/remarked 601's from China? I bought the 80MHz part from China from a seller known to sell both fakes and legitimate CPUs and, while unlikely, I'm still paranoid my CPU could be a 66MHz re-badge. I would be really surprised though since 601's aren't really collectible or sought after.

Also, does anyone know what the 31.3344MHz oscillator does on the board?

 

[Arbee]

31.3344MHz is an important clock in 68K Macs. It's 4 times the original Mac 128/512/Plus clock, 2 times the Mac II/IIx/IIcx/SE30 clock, and so on. Lots of other chips like IWM/SWIM and the VIA used clocks derived from that as well. As a wild guess, it's used to slow the 601 down to match various older support chips so the system works.

 

[eharmon]

You probably bought the same 80MHz part I did to try to repair my broken upgrade card. PPCA601FF-080c-2? It looks pretty legit to me, but I haven't tried mine yet. It's much harder to fake these because the glass/epoxy(?) packaging would show any damage from grinding off the label and printing a new one.

Now, if they're entirely bad parts is anyone's guess, but if it boots at 66MHz it seems unlikely.

My 66MHz upgrade card does run quite hot without active cooling, pushing to 80MHz has never worked, it can only hit about 72 or so. Given yours does boot from cold, I would look at heat first. I believe the PPCA601FF (emphasis mine) is a pretty late stepping/mask. But I've never found any details on the improvements from the earlier PPC601FC found on many (most?) upgrade cards.

That said, there's 2 major revisions of these cards, and some with larger and smaller ROM chips, so there's some variation between the cards themselves which might imply the 80MHz are specced for faster parts. I'm not aware of a detailed comparison between the revisions.

 

[willmurray461]

Yeah I bought a PPCA601FF-080c-2. I don't think they would be hard to fake, since you could probably remove the printing with some kind of solvent. The labeling seems to sit on top of the package, rather than being imprinted into it. However, if they were fake, they'd probably re-mark them as normal PPC601s, not PPCA601s. Either way, it's probably very unlikely since, as far as I know, there is not much of a market for 601 CPUs.

For what it's worth, I have the later revision card with the 512 x16 ROMs.

I'd be pretty surprised if the heatsink wasn't enough to cool the CPU, given how large it is. I still suspect the cache chips are at fault. I'll post an update once I can swap the 10ns parts in.

 

[eharmon]

Yeah I bought a PPCA601FF-080c-2. I don't think they would be hard to fake, since you could probably remove the printing with some kind of solvent. The labeling seems to sit on top of the package, rather than being imprinted into it. However, if they were fake, they'd probably re-mark them as normal PPC601s, not PPCA601s. Either way, it's probably very unlikely since, as far as I know, there is not much of a market for 601 CPUs.

For what it's worth, I have the later revision card with the 512 x16 ROMs.

I'd be pretty surprised if the heatsink wasn't enough to cool the CPU, given how large it is. I still suspect the cache chips are at fault. I'll post an update once I can swap the 10ns parts in.

It's large yeah, but mine gets burning hot to the touch. I had some airflow problems and ran into similar symptoms...it only worked when it was cool. That said, that's with the FC rated at 66MHz.

But the cache chips isn't a bad theory so I'm interested to see if that turns out...maybe my working card has a similar fault.

 

[willmurray461]

The 10ns parts from Mouser arrived today and I am pleased to announce that the Apple PowerPC Upgrade Card now works stably at 80MHz! I haven't really tried pushing it with games or anything, but it was still working after half an hour or so of sitting on the desktop.

There are still some very minor signs of graphical artifacting, but only when using the 601. For some reason, with the 40MHz '040, there aren't any graphical issues.

These issues might go away if I swap the original 80ns VRAMs for some faster ones. Anyone have a boring-ish donor card with 70ns 128k x8 VRAMs they'd be willing to sell me (something like a 7100 HPV or AV)? Has anyone ever seen 60ns 128k x8 VRAMs?

By the way, if anyone wants to try this mod themselves, here are the SRAM parts that I bought:
128k x 8
32k x 8

 

[willmurray461]

Just thought I'd share an update for anyone who's curious.

I managed to get my hands on some 70ns VRAMs. Soldering them onto the Quadra 800's motherboard did not fix the issue. My guess is that you'd need to change timings in the ROM of the PPC Upgrade Card in order to get things to work without artifacts (or maybe 60ns VRAMs, but I've never actually seen 60ns 128k x 8's even though datasheets say they exist).

However, I did put the card into my 40MHz overclocked Quadra 950 and it works flawlessly. The 950's video circuitry has no problems running at 80/40MHz with the PPC upgrade card, which is very nice.

 

[Elv1s]

Just thought I'd share an update for anyone who's curious.

I managed to get my hands on some 70ns VRAMs. Soldering them onto the Quadra 800's motherboard did not fix the issue. My guess is that you'd need to change timings in the ROM of the PPC Upgrade Card in order to get things to work without artifacts (or maybe 60ns VRAMs, but I've never actually seen 60ns 128k x 8's even though datasheets say they exist).

However, I did put the card into my 40MHz overclocked Quadra 950 and it works flawlessly. The 950's video circuitry has no problems running at 80/40MHz with the PPC upgrade card, which is very nice.

Is there a guide how to do this or can you describe the process?

 

[willmurray461]

It's just like any other kind of SMD desoldering/soldering work. You'll need a hot air rework station and some flux to remove the old ram chips, then you can install the new ones either with the rework station or with a normal soldering iron.

If you've never done SMD rework, I would suggest practicing on a good amount of scrap boards before attempting something like this. You can check YouTube for tutorials.

Either way, replacing the VRAMs on the Quadra 800's motherboard doesn't really seem to help with anything. Maybe it would help if you're trying to overclock the 68040 to 50MHz, but at that point you might also want to try changing the Gestalt ID to the unreleased 40MHz machine to make the ROM timings more lenient.

Replacing the SRAMs with 10ns ones can make a difference for the PPC card though, especially if yours has 17ns SRAMs. If you have 15ns ones, you might be able to get away with keeping them.

 

[Joopmac]

I tried this today, 601 card in Quadra 700 with 800 board @ 40Mhz
Norton says 80Mhz, everything seems to work but i have three vertical lines. First i thought too slow VRAM, but also 70ns in the slots doesn't work. On-board is 80ns...