Centris / Quadra 650 / 800 Behaviour When LEDs are Fitted

Previously I've had someone (sorry, I can't find the old posts, I can't remember who it was) tell me that fitting an LED to the "desktop" LED footprint will change a Quadra 800 into a Quadra 650, which caused confusion because that contradicts how my Centris 650 behaves (if I jumper the J25 tower (Frigidaire) LED header and have the desktop LED, DS1 fitted, my machine reports as a Quadra 800, even though the DS1 is fitted).

Looking at the schematic, I can see there is faint pen markup correcting the labels for the two LEDs. This markup corrects phrasing from the assumption that the 650 is a desktop at 25MHz, and the 800 is a tower at 33MHz, to just that the 650 is a desktop and the 800 is a tower.

I considered if perhaps the ROM revision changes behaviour, but looking at the schematic, this can't be the case. "LED_Pwr" is jst a test point to check that the LED is getting power, so there is no way in this circuit to detect if DS1 is fitted or not. On the other hand, a jumper included in the tower LED cable causes "CPU_ID_ext3" to be pulled down (overpowering the built in pullup) and sends a signal indicating that the tower LED is fitted... i.e. this is a Quadra 800.

In the following, "For 33MHz" and "For 25MHz" have been crossed out and an almost illegible notes written. 33MHz has been replaced with "Frigidaire", the 800 case. I can't read the other, but it probably says "Lego", the name of the 650 case.



Has anyone else seen their machine gestalt change from modifying DS1? If would only make sense if the circuit design was modified, I'm really confused by the suggestion.

First, you have original schematics for wombat? How does one acquire those?

On my actual Q800 board DS1 is not populated, but I have two Q650 boards with DS1 populated that report as Q800 if the jumpered led is installed. I'm not sure if I've ever tried the actual Q800 without the jumpered led, unfortunately I can't check right now because it's in storage...

I don't have a C650 board.

lobust said:

On my actual Q800 board DS1 is not populated, but I have two Q650 boards with DS1 populated that report as Q800 if the jumpered led is installed. I'm not sure if I've ever tried the actual Q800 without the jumpered led, unfortunately I can't check right now because it's in storage...

Click to expand...

What you're reporting matches what I've experienced.

Phipli said:

...schematic...

Click to expand...

That is awesome, thank you!

A Quadra 650 should be 33mhz. The Centris ran at 25.

I was the one telling you that. If neither is populated, it reports as a Q800, just like if you have the jumpered LED connected. If only DS1 is present, then it reports itself as a Q650. Now, it's possible that the Q800 board I had in 2014 was a weird one, but that's how it responded when the LED was added to the board and the board was reinstalled into the C650 chassis I had. Before LED was added, even though it was in a 650 case, it said Q800. After LED was added, it said Q650.

volvo242gt said:

I was the one telling you that. If neither is populated, it reports as a Q800, just like if you have the jumpered LED connected. If only DS1 is present, then it reports itself as a Q650. Now, it's possible that the Q800 board I had in 2014 was a weird one, but that's how it responded when the LED was added to the board and the board was reinstalled into the C650 chassis I had. Before LED was added, even though it was in a 650 case, it said Q800. After LED was added, it said Q650.

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Very strange. If your's behaves like that, it doesn't match the schematic. It isn't possible for that circuit to detect if DS1 is there or not. Unless Led_Pwr goes somewhere, but it doesn't go to the chip that has the rest of the model detection pins, or anywhere else I could find other than the test point. Plus it would be redundant.

Is there any chance you shorted something on J25, because it's actually purpose is to identify if it is a tower or desktop. The pin CPU_ID_ext3 is just there to tell the ROM and OS that you have a tower, it has no other purpose. Clock speed and logic board are covered by CPU_ID_ext1 and 2.

My Q800 board came from the factory with both fitted.

No, the J25 jumper was not shorted. So, there's something incorrect about the schematics. Try installing the 800 board in a IIvx or C/Q650 case, without J25 connected, but with DS1 present. If it still reports as a Q800, then, maybe someone modified my board, but it should not have then changed to a Q650 board when the LED was added.

Thanks for this thread. I recently dug out my Q800 board in a desktop case from waaay back, but noticed it identified as a Q650. I don't remember it ever doing that before, and I recall it ran A/UX without modification (which I didn't think was possible) but maybe I'm, uh, misremembering. Anyway adding a jumper to pins 2 and 3 on J25 fixed it. FWIW I also have a Q650 motherboard, but J25 doesn't have the header on it, so I guess that's an easy way to tell these boards apart (aside from the heatsink if that's still original.)

shascall said:

Thanks for this thread. I recently dug out my Q800 board in a desktop case from waaay back, but noticed it identified as a Q650. I don't remember it ever doing that before, and I recall it ran A/UX without modification (which I didn't think was possible) but maybe I'm, uh, misremembering. Anyway adding a jumper to pins 2 and 3 on J25 fixed it. FWIW I also have a Q650 motherboard, but J25 doesn't have the header on it, so I guess that's an easy way to tell these boards apart (aside from the heatsink if that's still original.)

Click to expand...

My C650 came with a heatsink, and I've seen a Centris 650 and a Quadra 800 board with both LEDs and both speaker headers fitted! Sometimes couldn't decide what to do!

Glad the thread was useful