Troubleshooting a Quadra 840av

[luckybob]

Thanks to someone on another forum, I got access to a Quadra 840av. Long story short, I bought it for $75, because it did not post. The person selling it was about as illiterate about macs as I am therefor I was hoping it would be a simple fix, and worst case scenario, the main board needing a re-capping.

It arrived this morning, very well packaged. It is significantly yellowed. I would call it "fair" condition:



I have 2 extra bezels, one for a cd drive, and another blank one. I will need to test my JB-WELD skills as 2 tabs broke off during shipping. These were on the front face. Anyway its not a big deal. I crack the box open, and remove all the accessories that were packed inside. Extra video card, network adapter, keyboard, cable, etc. I remove the 4 completely random looking ram sticks, in favor of 2x 32mb simms from my quadra 660av. Thus eliminating the possibility of bad ram. I also take the original looking pram battery out and pop in a new one for good measure.

I apply power and IT POSTS, then boots to system 7.5! This image represents how I looked at the time:

In my zeal, I power the system down, remove the hard drive. For some reason it had a 160mb affair in it. I shrugged and laid it aside. I figure I will use in it my LCIII as a system stock drive. I also install the apple cd drive from my 660av as well. I boot it up again to see if it would take the 8.1 install I had on the drive. Instead I get the standard post chime and a grey screen. (moveable mouse cursor)

I shrug it off, thinking I'll need to use my boot cd and re-format. I decide to see if the add-on video card I got worked. I figured it would be better to do it now than after I close it up.

Slot #2 already had its cover gone so I pushed the card in with a satisfying click move the video cable and hit the power button. NOTHING. no post. no beeps. It doesn't look to be a special card but I had to know. Here is a picture:



Here is where everything goes tits-up. From here on out, the machine refuses to post. (no sound, no video) Nothing I know to do has worked, including:

removing ALL cables

re-seating the cpu

re-seating the ram

different ram

cmd+opt+P+R

goat sacrifice

all caps look PERFECT, including in the psu. The board looks brand spanking new.

no visible physical defects

I figure now is a good time to take a break and ask for assistance from those that might know what they are doing.

 

[Macdrone]

Ok I am not sure about the quadra but I have the desktop G3's and they do the same thing. The issue happened when the OS forced a resolution the motherboard basically froze just like what you mention. I had to boot from CD and on board video (holding c key) and then install the software for the video card. I hope this gives you some options.

Good luck.

 

[luckybob]

Then it would work without the video card, right? I've tried booting the board with only onboard video, speaker and power supply plugged in. no dice.

 

[Macdrone]

How about hitting the Cuda button the motherboard, also I had to switch on then off then on again the first boot even after hitting he switch. Again I don't know why I tried it or why it worked. But it worked on three G3 desktops that would not do anything after people tried to load OS X on them. I know yours is an 040 but just trying to say forced video and something (maybe in rom) gets sideswiped by the video (only just guessing and shooting in the dark).

Again best of luck

 

[luckybob]

cuda button? the only button on the mainboard is the power button.

 

[Byrd]

Leave it unplugged for 2 - 3 days and see what happens. Sounds like a comparable issue with my 840AV, which worked perfectly if not used for a while but would not boot if you restarted or shut down/restarted. I switched the power supply to no avail, RAM, etc - and eventually replaced the caps, which resulted in a reliable machine that would fire up every time. The boards also seem to get really dusty in these cases, and the silver lining corrodes quite badly, so give the internals a good clean out too with compressed air.

JB

 

[beachycove]

I have had two 840av machines, and had similar problems in both cases, involving erratic booting/ non-booting. The machines would power on sometimes, but generally would get no further than a grey screen. This is going back as many as 6-8 years.

The trouble, I discovered, was that capacitors had leaked on both near the main power connector on the logic board (look closely for residue). The rest of the board looked fine. A good cleaning cured the problem and both then booted normally.

One unit was subsequently sold working; the other is still running fine here in the house, is more or less pristine, and is very unlikely ever to leave my collection. I have not yet needed to recap, though obviously that day will come eventually.

 

[luckybob]

see, that's the thing. when I look at the board, it looks practically pristine. There is no evidence of leakage near any of the caps, specifically near the power connector. Should I just go ahead and do it anyway?

 

[beachycove]

Will it boot if you set it up as it came delivered to you, hard disk and all?

 

[James1095]

It's not uncommon for capacitors to *look* pristine when they are in fact completely shot. I can't say for sure whether this is your problem, but capacitors have to get really far gone before a visual inspection will turn up anything. Unless you have an ESR meter, the easiest thing to do is just replace them.

 

[luckybob]

Will it boot if you set it up as it came delivered to you, hard disk and all?

It did once when I started. 2nd and 3rd attempts were grey screens. 4th and beyond , all black screrns with no chimes.

It's not uncommon for capacitors to *look* pristine when they are in fact completely shot. I can't say for sure whether this is your problem, but capacitors have to get really far gone before a visual inspection will turn up anything. Unless you have an ESR meter, the easiest thing to do is just replace them.

Looks like im going to be doing that. Looking at mouser.com for a set of nichicons.

 

[James1095]

If there are any surface mount electrolytics, replace those with tantalum or ceramic chip capacitors. They're a little more expensive but they will never leak. For through-hole electrolytics, look for low-ESR types rated at 105C. Nichicon is a reputable brand, as are many others.

 

[Byrd]

If all other basic troubleshooting has failed (eg. try more RAM, check power supply voltage lines, clean connectors/board, VRAM etc etc), then yes I would replace the caps with tantalum replacements. I did mine a few years ago and it wasn't as bad as say doing an SE/30 nor were there as many to replace, if I recall. Some caps were a little difficult to remove though so be careful to not pull up any traces in the process.

JB

 

[luckybob]

If there are any surface mount electrolytics, replace those with tantalum or ceramic chip capacitors. They're a little more expensive but they will never leak. For through-hole electrolytics, look for low-ESR types rated at 105C. Nichicon is a reputable brand, as are many others.

I was going to get these:

http://www.mouser.com/ProductDetail/Nichicon/PCX1C470MCL1GS/?qs=sGAEpiMZZMtZ1n0r9vR22UdLYVQX4pPxWiS5P1Zoi%252bM%3d

But according to your suggestion, these would be better:

http://www.mouser.com/ProductDetail/Nichicon/F911C476MNC/?qs=gmcn8Ik9O3ES451T9B7NoQ%3d%3d

I've always been under the assumption the metal cans like these don't leak. *shrug*

 

[trag]

You may wish to consider purchasing replacement caps from me. See this thread in the Trading Post:

http://68kmla.org/forums/viewtopic.php?p=156070#p156070

 

[James1095]

The metal cans most certainly DO leak. Granted they will probably be just fine for at least a decade, but *every* 68k Mac I've dealt with that uses these has had them leaking all over. The tantalum caps trag sells are just fine, I bought the same type in bulk for my re-capping work.

Best way to remove the old capacitors is to do it cold as the heat from a soldering iron weakens the adhesive bonding the pad to the PCB and combined with the corroded solder it's very easy to damage the board. use some small diagonal cutters and for the larger caps grasp the can and gently bend it over, the leads will pull right out or come unsoldered. For the smaller size ones, cut them off as close to the base as you can. Either way you then clean up the pads with a soldering iron and solder the new caps in place. It takes just a few minutes unless you have a lot of corrosion damage to repair. Make sure you get the polarity right, tantalums like to blow up if you get them backwards.

 

[luckybob]

update. I took out the mainboard and really scrutinized the caps on it. Turns out the 2 10uf caps around the scsi area are slightly leaking. I do mean slightly, but it means one thing. NEW CAPS!!! I have 2 other motherboards waiting for a re-capping. So I might as well get all at once. Practice on the two other first, naturally. I do appreciate your offer Trag, however I must get Nichicon caps. I'm pretty brand loyal.







On a unrelated note. The macro mode of my Samsung Galaxy S3 is AMAZING.

 

[trag]

I do appreciate your offer Trag, however I must get Nichicon caps.

No problem. I am happy that folks are fixing old Macs no matter where the parts come from. I started selling sets of caps because many folks who were willing to solder, were intimidated by identifying and ordering replacement caps. So I make it easier for those folks who aren't comfortable sourcing their own parts.

 

[Trash80toHP_Mini]

That service is much appreciated, as is the recap parts-listing. I haven't started yet, but the Macs I play with all work fine so far.

An official detailed recapping guide for every model would be an excellent thing to have in the Hacks & Development forum. I know we have some already, but I'll have to think about some sort of formatting for entries. I'll start with one of the boards I need to tackle first, Im thinking along the lines of having a pic of the MoBo with info boxes, witnessed lined to each cap on the board and a netlist of caps . . .

< scoots off to . . . >

Capacitor Replacement Thread . . .