• Hello, Guest! Welcome back, and be sure to check out this post for more info about the recent service interruption and migration.

Has anyone actually installed a 55/65xx board in a pre-PCI Mac?

Franklinstein

Well-known member
I have seen several references that supposedly the 55/65xx Gazelle boards have an onboard 3.3v regulator which allows them to be installed into an older chassis (Quadra 630, Performa 588, 52/62/53/63xx and similar machines) without supplying 3.3v from the power supply like the Alchemy boards (from 54/64xx machines) require. However, upon trying this, I have had no luck: the boards either refuse to boot, or something doesn't work properly; for me they'll only work in machines where they're supplied 3.3v from the power supply.

I have tried a couple different Gazelle boards in a few different non-3.3v chassis and had the same results: no boot, or weird problems with disk access or something that disappears when these boards are used in a proper 3.3v chassis or the original boards are reinstalled.

Does anyone have experience of installing a Gazelle board into an older (pre-54/64xx/6360) chassis without modification? Or is this just a misconception?

 

Trash80toHP_Mini

NIGHT STALKER
I ran a Gazelle board in a 6290 something like15 or 16 years ago with no apparent problems. But that was just playtime, never really put it through its paces. I've still got most of the bits fairly handy to see if I can confirm your results or report no problems when I find all the pieces and get them all together on the bench. There are so many reports out there that it works that I've never doubted it.  :huh:

 

Cory5412

Daring Pioneer of the Future
Staff member
With the warning that I might be remembering this wrong because I never had enough of these machines to bother doing this:

If I remember correctly, the issue was either with one specific board or set of boards having or not having the appropriate conversion hardware (I'm tempted to say the 6360 "has it" but I can't say for sure) or with PCI cards, or the PCI riser being installed at all.

I trawled around Zone 6400 and the information wasn't there, likely because nobody on that site was very interested at the time in putting a board in an older machine, such as a 580 or 630.

 

Franklinstein

Well-known member
I think it's more of a thing in the mod community, specifically with those building a Power Color Classic. It's easier to build a PCC without a 3.3v power supply for PCI-based boards, but supposedly some people were able to install a 55/6500 board without the 3.3v supply because it's supposed to have an onboard 3.3v VRM that operates from either the existing 5v or 12v lines. If that was the case, though, why do 55/6500 harnesses supply 3.3v to the board? Maybe the TAM board has one since  apparently its big external power unit doesn't supply 3.3v, but I'm more inclined to believe that its 3.3v power supply is inside the main body, not on the logic board. 

 

Franklinstein

Well-known member
Im really only interested because I'd like to speed bump my other MPC-LX200 from its 6300-based board to a 55/6500-based board without modifying the harness. I tried directly swapping it but after powering up there was no chime and an acrid smell causing me to immediately abort that experiment. Restoring the original 6300 board to the MPC resulted in it booting just fine, while the 5500 board booted up when it was installed in a 5400 chassis. This isn't the first time I've experienced failure doing this sort of swap though, hence the question of whether anyone has verified success doing it. 

 

Trash80toHP_Mini

NIGHT STALKER
Yeah, I was going to suggest looking into PowerCC lore for info. Checked into your statement that the harnesses are identical or at least supply 3.3v. There's no part number for the harness, it's availability was restricted to the chassis/harness combo. PSU is the same from my read, but the Rev.A and Rev.B chassis harnesses could be different. Such might be the ONLY difference?

6400-6500-sploded.JPG

Dunno, 6500 works fine in 6360 and 6400, but I don't recall trying either one with the 6500 harness and PSU. When I unearth the 6290 for a bit of playtime, I'll see if I can find the 6500 harness for a part number comparison to the 6400 setup on the bench ATM. Gotta look for the 6500 PSU as well  .  .  .

.  .  .  remembered I piled the harnesses in a file transfer box under the bed behind me! Rummaged through it pretty well, but no help. One is from a desktop labeled FoxConn 080-0003-192 and two are the same part number, but configured for MiniTowers (6500 IIRC, one from a FuglyTower I put down and one came from an eBay seller with the Logic board from a 6500 that he put out of his misery) and they aren't even identical! The one in the 6400 kit on the bench isn't even a FoxConn part. It's made by T&B with Apple P/N: 390-9997. No 6500 PSU found for comparison, that calls for deep diving into the hoard.

Methinks your assumption that the 6500 harness necessarily supplies 3.3V might be in question.

My head hurts all of a sudden. :p

 

Franklinstein

Well-known member
If you notice from the above diagram, all of the boards referenced are PCI-based, both Alchemy (EDO boards, 3.3v always required from harness) and Gazelle (225MHz+ boards, 3.3v in question). Since both types of boards work in the same chassis, the harness must always supply 3.3v to the logic board. This suggests that the Gazelle boards do require 3.3v, or at least expect it to be supplied whether it's used or not. 

As for harness part numbers, there may be more than one: the harness itself is physically identical to that originally built for the Q630, the only difference being power wiring and possibly cable lengths to suit different cases through the years. So there could be both a mold part number and a wiring loom part number printed/molded onto the part, both of which may be different from the actual Apple part number. The '90s were a confusing time at Apple.

While i do have the other harnesses handy, I don't have a 55/65xx to compare to. Maybe I can look at the TAM if i can see the harness from the back without disassembling it. 

 

jupo

Well-known member
I have an empty 580 shell, a 5260, and a 5500/225. Would it help for me to swap boards around and see what works, or look for psu voltages? 

 

MJ313

Well-known member
I have tried a couple different Gazelle boards in a few different non-3.3v chassis and had the same results: no boot, or weird problems with disk access or something that disappears when these boards are used in a proper 3.3v chassis or the original boards are reinstalled.


Hi Franklinstein-- I was wondering if you got anywhere with this issue? I am having fun with the same thing... I have a 6300 and have had good luck with a modified 6400 board with 3.3v regulator, but when I try a 6500/225 (no modifications) the machine has disk issues, similar to what I think you experienced. My initial thought was a power issue because the 6300 supply is reportedly weaker than a 6360, but then I got to revisiting the 3.3v issue and came across your thread. I can't find an example of someone getting a 6500 board to work in a 6200 or 6300 (However, a 6500 board will work fine in a 6360). Maybe there are just gremlins with my setup.

 

Franklinstein

Well-known member
I had to put a 3.3v regulator on the line to get it to work. I don't know how people supposedly got theirs to work without it but mine don't. I figure the onboard regulator on the Gazelle boards is either a backup or auxiliary rather than intended to be a primary supply.

Also, the pre-PCI models have a slightly different power line pinout on the harness that uses three ground wires where the PCI models swaps one of those wire into a 3.3v supply, which explains the no-boot and bad smell when I attempted to slot a PCI board into a pre-PCI chassis (you're essentially running ground to what is supposed to be the 3.3v supply if you do this). So if you're attempting to do a mod like this, you'll want to remove the one ground wire from the harness and ideally put a 3.3v power supply on it instead. 

 

MJ313

Well-known member
Thanks very much! That's very helpful and gives me hope-- I'll get a 3.3v regulator and wire it in.

 

trag

Well-known member
I've used these little modules from time to time.  They're widely available and pretty cheap on Ebay.  

https://www.ebay.com/itm/10pcs-New-Low-Ripple-LM2596-DC-Converter-Buck-Step-Down-Power-Supply-Module/251261373643

There was some reason I settled on this seller, though.  I can't remember exactly why, but I think it had to do with examining the datasheet for the regulator driving the board and looking at the components used with it.   Some of the regulators available seem to be using under spec'd parts, if I'm remembering correctly.  It's been several years since I looked at this.

 

johnklos

Well-known member
It was all too confusing to me, so when I had a PCI board, I just removed the maybe-3.3 volt / maybe-ground pin and fed the motherboard from a physically installed 3.3 volt regulator:

fifi_3.jpg

fifi_1.jpg

 
Last edited by a moderator:

MJ313

Well-known member
Thank you!  That's exactly how I got my 6400 to work, following your 'guide' above. Since it sounds like the 6500 needs the same remedy (and the remedy won't cause any problems), I'll just do the same thing. And thanks to trag for the ebay link and to Fizzbinn for the powercc source!

 
Top