g4 mdd fw800 chimes with no video

[chiggen]

(this post is similar to some others but I feel it's different enough for it's own post)

My fw800 (dual 1.25Ghz) mdd's psu died a while ago so I replaced it with a cheap Thermaltake 600W atx psu with a conversion cable from ebay. It works fine, however it's too big to close the case so I bought a SilverStone SST-SX500-LG sfx psu (which is 500W) and when I use it instead of the 600W one, the computer chimes but there is no video. I tried removing all the pci cards and unplugging the dvd drives and hard drive but it still doesn't work with the 500W psu but works fine with the 600W one. I have a 350W flex atx psu that also has the same symptoms when I use it with the mdd but the 350W probably just isn't enough to power the mdd. I'm a bit confused as to why it doesn't work because iirc the stock psu is 450W so the SilverStone should work? My mdd has 2GB of ram, no PRAM battery, a radeon 9000 pro, rage 128 (which I don't have a monitor that I can test with), and nec usb 2 card if that helps at all.

 

[chiggen]

I have also tried removing all the ram DIMMs as suggested here and it beeps

 

[chiggen]

I can do a pram reset with the 600W but not with the 500W

 

[Byrd]

It can be an exercise in find the right modern PSU replacement in older Macs and PCs. It can sometimes be related to the new PSU providing low amps on certain rails, no -12V rail or not confirming to an older ATX specification. It sounds like some of the modern ATX PSUs you have tried are struggling to provide sufficient amps on some rails. Are you using an Apple ADC display at all?

This are the specs of the 360W MDD PSU, note relatively high amps required on +5V (many new PC components have high +12V amp requirements). Do your replacements conform approximately to this?

Noting you had better luck with a 350W SFF PSU (which might be older with higher amps on what you need), unless you have a card in every slot, a HD in every sled, a high-end GPU with additional power required and some sort of super G4 upgrade, 350W is sufficient.

 

[chiggen]

Thanks for the reply! I think I had the 400W acbel PSU. I'll try to check to make sure my PSUs conform tomorrow. Just to confirm, it is exactly the same with the 350W and the 500W PSUs (it chimes and the power button and mobo lights turn on but no video). Again, thank you so much for the reply! (I am sorry if this reply sounds very negative, I do not mean it to be)

 

[chiggen]

so I have just checked all the PSUs and they're pretty much all the same voltage-wise:


except the 600W one (the one that works) has an extra +12V listed?
I found an image of the dc output for the acbel supply and it has the same voltages as the image you posted and is 360W so I guess I had a 360W PSU originally. Below is the image:

This has just made me more confused as to why the 600W one works as all three PSUs have two +12V rails (at least according to the below image)

Thanks so much again for your help and I hope this helps!

 

[Byrd]

Sorry didn't read correctly in that the 350W PSU you tried didn't work (and you're not negative at all!). Makes you wonder why the 600W works over the others when technically it's the least compatible.

More into here suggests your Apple Radeon 9000 graphics card is the issue and will not work off most ATX PSUs (without +25V) even if plugged into a DVI monitor (no ADC monitor in sight):

Mac Classic

Tips and tricks to help keep your Mac OS 9/Early Mac OS computers usable today. Software downloads, guides, hacks and news.

mac-classic.com

... therefore try a PCI video card or PC flashed AGP GPU?

More info here on Radeon 9000 and MDD:

I Need Help Getting A Video Signal To My G4 MDD Using An ATX Power Supply.

This is an off-shoot from this thread: https://tinkerdifferent.com/threads/g4-power-supply-swap-adapter-cable-has-the-wrong-connector-from-atx-ps-to-adapter-cable.3374/ The G4 MDD is hooked up to my 32-inch Panasonic Viera TV (2010). My 2010 Mac Mini is hooked up to it as well. Note the...

tinkerdifferent.com

MDD FW800 PSU replacement: No picture.

then best bet, refer to this thread for help with your psu adapter. has to be a wire or two that's out of whack G4 MDD ATX PSU Conversion

forums.macrumors.com

... the last link suggests using a step converter from a +12V rail to to get to +25V for the stock video card to function

 

[chiggen]

I just tried plugging the rage 128 into a monitor with vga (that I know works perfectly fine with other computers) but still no video from the mdd. I have noticed, however, that the radeon 9000 gets a bit warm when the computer is turned on, even though it's not outputting anything? There also seems to be no usb power but maybe that's normal when there's no hard drives? I have a spare ati radeon 7000 from a pc but I don't have any other computers with agp at the moment and I don't really want to go through the trouble of flashing it.

 

[chiggen]

I measured all the voltages on all the PSUs and they are all (within reason) the same:

 

[chiggen]

I realized I missed the cpu power:

the +12V pins are by the latch on the connector (below image shows what I mean)

 

[DarthNvader]

Try and remove the R9000 when testing the Rage128 for video.

If the Radeon is partially coming up it maybe trying to divert video to that card.

Removing the Radeon should be enough to get you boot video from the PCI Rage card.

Otherwise you may have another issue.

 

[chiggen]

I removed the radeon but still no video, even with the 600W PSU (the one that should work). The rage128 does get warm though. I haven't tested it before though and don't have another Mac to test it with so I don't know if it works. My USB pci card also seems not to have any power, or at least keyboards plugged into it don't. To clarify, I haven't plugged in the DVD drives or hard drive in many of my tests, if that effects anything.

 

[Byrd]

Did it reliably boot with the 600W + Radeon 9000 at the start or was intermittent? Can you get some video output with just the PCI card, PRAM reset and 600W?

Hmm I’d be checking the CPU next clean connectors, clean PCI and RAM slots. What is the CPU installed - stock of upgraded?

 

[chiggen]

It reliably booted with the 600W + Radeon 9000 at the start. I am pretty sure I can't get video with the pci card, pram reset and 600W. I am unsure whether the cpu is upgraded or not as the computer hasn't always been mine but it looks stock. A friend suggested that because the 500W PSU is providing 40A on the +12V where the stock 360W provides 16A the mdd might be going into something similar to overvolt protection? This makes sense to me as the 600W (the one that works) only does 23A or 20A there and the 350W does 29A but I'm not sure if the mdd gets angry when the PSU gives too many amps.

 

[chiggen]

Good news! I got a 400W flex ATX psu and it semi-reliably works now! I occasionally lose video (though as of yet not when I'm doing something with the computer) but that is probably due to either the bad adapter I'm using to convert the atx pinout to the mdd pinout or the high temperature in my house.

If anyone wants to know, the amp values for the new psu are below:
+3.3v @ 10A
+5v @ 16A
+12v1 @ 21A
-12v @ 0.5A
+5vsb @ 2A
+12v2 @ 21A