troubleshooting Quadra 800, no power up

[wilykat]

I just got it in today and I've looked over the motherboard and parts.  The battery hasn't exploded but it was dead (blue label Inorganic brand) I replaced it with a good purple battery. Removed the extra memory, the only Nubus card (ethernet but has 15 pin connector and old base-2, guess someone was too cheap to pick up Apple transciever and use onboard ethernet?~) and disconnected the hard drives to rule out faulty short.

However it doesn't boot up. No chime, no light, nothing.  I don't have 800 or 8100 mobo to test with and I don't have extra power supply of these type to swap with. Where can I start poking for problem?

 

[olePigeon]

Do you have a multi-meter?  Make sure the power supply is good.

 

[uniserver]

probably leaky caps in the psu.

 

[Elfen]

Leaky caps and a bad Signal Diode in the PSU. Can you do a jump start with a battery like on the Mac IIs? You need to set up the + battery wire on the PSU output and then touch ground.

 

[wilykat]

Leaky caps and a bad Signal Diode in the PSU. Can you do a jump start with a battery like on the Mac IIs? You need to set up the + battery wire on the PSU output and then touch ground.

Going to be tricky to try the battery trick. When the motherboard's installed the battery and power connector is blocked on motherboard side. I could only access the power supply on top if I unplug the motherboard cable.

I'd have to see about trying to flip the motherboard over to access everything and test there.  Is this pinout right?  Hard to actually find power supply pinouts

orange.... +12 

blue.... -12 

yellow.... +5 trickle 

white.... power on 

red.... +5 

black.... Gnd 

 

[wilykat]

Quick update: with the power plug in, I checked all of the pins. There are supposed to be a standby power but I got 0 on all of the pins.  I also tried the battery jumpstart trick, nothing worked.

 

[wilykat]

https://discussions.apple.com/thread/2171912?start=0&tstart=0

Tried the trick with the power supply unplugged from motherboard and drives.  Still won't turn on.  I opened it and only found one fuse (checked good) and no obvious issue like bulging cap or burn resistor.  Only one obvious relay and it's wired with coil on 12v side and N.O. contact across hot wire connecting to second power port for monitor or peripheral, doesn't do anything on the main power in.  4 individual PCB boards all soldered together and lots of parts makes this a bit hard to troubleshoot. I'm not de-soldering and checking every resistors, every diode, and replacing all 40 or so electrolytic caps.  There's about a dozen transistors and regulators which won't be easy to test if they aren't plain vanilla transistor (don't have anything to test for FET, regulator, switching IC, etc)

 

[uniserver]

usually its just the filter caps, lots of the time they leak at the base and you can't even see it. 

the filter caps are right near where the the wires that go to the connector are.

usually 1000uf 16v, or 2200uf 16v, or even 6800uf 16v type caps.

 

[wilykat]

There are probably 6 caps directly connected to power out on the PSU.  I remembered an old trick for checking a switching power supply. Using ohm meter and with no power, check the pins with respect to ground.  Good rail should be almost 100 ohms.  I got 40 ohms on 5v and 5v standby while +12v looks OK.  -12v has different rule because of negative supply.

I sure could use a schematic. I tried for Delta power supply but got nada.  PCB board labeled DC-266 (on top of PSU if the PSI is mounted in Q800/840) is mainly for mains input, relay to switch on power out for monitor or peripheral, some filters, chokes, and a fuse, and 12v plug for internal fan.  Theoretically I could remove this board and feed a clean regulated 120v AC directly.

 
The 2 main boards are labeled SMP-220DP and comes in 2 section boards for voltage regulation, the vertical board (on left side if the PSU is mounted and you're facing the front of 800/940) )handles most of AC to DC conversion, the horizontal board (bottom of PSU) seems to be AC with 110-220 switching, and +5 standby comes from a small area of the board.  The last PCB board (on front of PSU) is a small one marked DC-267 and appears to be the last part where regulated power goes through before it reaches the motherboard connector.  I'd need to do more work to figure out what function each section actually does.

The capacitors that I think are part of final filtering are nested in a tight area between transformer and 2 PCBs and held down by white glue so it'd be challenging to remove those without breaking something.  Just about all of the PCB seems to be single sided and single layered so it'd be easy to desolder and remove.  I can provide picture if someone wishes.

BTW still looking for working replacement, want ad is in trade section.  PSU is Delta SMP-220DB and Apply part number 614-0012. I am sure PowerMac 8100 will also work as they are similar overall.

 

[wilykat]

Got a replacement PSU in.  5v standby checked good. Plugged it all in, power on

BOOOIIIINNNNG!!!

It works!!  The hard drive included had OS 7.6 and a bunch of old files from a check apps. The last date were over 15 years so it's a good bet any sensitive info is useless. Going to wipe the disk clean and install fresh 7.5 then work on file transfers. No game or anything interesting for me there, I think it was primarily used to manage paycheck of a small company.  It keeps trying to access networked server which probably held the main database with names, addresses, and other info for printing checks.

First: recap. The startup chime sounded weak even at volume 7 so the caps are probably starting to go bad.  Remind me to take nice clean picture of the motherboard and note all the caps and its rating since I didn't find useful info for this specific model (or C/Q650 which has same layout)

Next: DOS card, and maybe a nice powerful SCSI card so I can boot faster than onboard SCSI Also the Video Spigot card and put in the memory sticks.

I discovered one issue: my LCD looks dang ugly if it's not run at native resolution of 1280x1024.  Yet some games won't run right if it's not set to 640x480 anyway.  I did check and it runs at 800x600@56Hz but looks about as bad.  I am using Apple supplied VGA adapter that originally came with Apple Basic Color Monitor so I am limited to this 2. I might look for a different adapter with switches to get higher res and use higher res for apps that do support it and go 640x480 for games.

PS with working PSU I can compare with dead one to trace voltage and find the dead part.

 

[Elfen]

Congrats and good luck with the Motherboard recap. Also try to recap that dead PSU, maybe you can bring it back to life and you will have a working spare in case the one you got now goes bad.