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#1 2015-07-07 10:25:43

bobo68
Member
From: Germany
Registered: 2015-07-07
Posts: 22

Quadra 650 does not start up - capacitor blown and a bit of mystery

Hi,

I acquired a Quadra 650 which was in very good visual condition but would not start up. I'll make the long story short: the Quadra has a blown capacitor C203 on the underside of its mainboard:

2015-07-04%2018.55.50.jpg

(the cap was initially "complete" but blown - one part fell off when I tried to clean the surrounding)

The "explosion" left some smoke on the housing:

2015-07-04%2018.53.29.jpg

Somebody put some clear tape across that part of the mainboard (obviously after the explosion):

2015-07-04%2018.53.41.jpg

The mainboard PRAM battery (which of course I thought was the reason for the Quadra not starting up) was probably installed the wrong way (polarity). I ripped the old one out quickly without checking but I think it was reversed. The battery is from 1997 and still has 3,6 V - another indication that it was installed wrongly because it should have been empty by now.

The PSU is working, I can start it up by shorting output pin Pin 9 (/PFW, power fail warning) and pin 10 (+5V.TRKL). It obviously cannot be started up by the Quadra.

There is a thin film of some sticky (dried up?) stuff on the underside of the mainboard. I thought that maybe somebody poured Coke etc. into the Quadra and the mainboard got a little bath but the inside of the lower housing is clean. The upper side of the mainboard is also pretty clean.

So:

  • Can someone make sense of this situation? What happened here? I do not think that the cap touched the lower metal housing and blew. Could the wrong polarity of the PRAM battery be the cause? Maybe the tape held the blown cap in place so that the Quadra would have worked years ago...

  • What can I do to permanently fix the damage? What cap is needed as a replacement? Can I just replace it with a wire (cap is not really needed maybe)? Do we have schematics for the Quadra 650?

TIA, bobo68

(repost from 68kMLA)

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#2 2015-07-07 10:34:20

uniserver
Member
From: Sf, Mi
Registered: 2014-05-15
Posts: 956
Website

Re: Quadra 650 does not start up - capacitor blown and a bit of mystery

what i would do is hot air off that cap...

i would use flux and wick to clean up those pads...

then i would remove all those electrolytic caps on the topside,  clean those pads up.
then wash that whole board really good...  hot soapy water...  get all that nasty Electrolyte, off the board...
Get all that coke that maybe did get spilt into the computer off...

then rise really well... and use a compressor and dry that board off asap.  Blast all the water out from under the I/C's

that cap on the bottom side might be reusable.   but more then likely....
the Caps on the top side are toast and that is what is causing your computer to not boot.

and install new caps!

also can you take a picture of the whole top side of the MB?


If cap goo has goo'd up the EGRET, its not going to boot up...  also if the EGRET is not getting its clock just like with the Color Classic, its not going to boot up.
https://www.thinkclassic.org/viewtopic.php?id=537

Last edited by uniserver (2015-07-07 10:39:05)


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#3 2015-07-07 13:25:57

bobo68
Member
From: Germany
Registered: 2015-07-07
Posts: 22

Re: Quadra 650 does not start up - capacitor blown and a bit of mystery

Thanks for your feedback, uniserver.

I guess we got a little off-track smile, so let me explain:

  • there are no electrolytic caps on the 650's mobo. That's one of the good mobos where Apple used tantalum (I guess)

  • hence there is no cap goo. The "goo" on the underside of the mobo is a thin film covering the whole underside. I maybe should wash it off anyway

  • the top side of the mobo looks nearly pristine - no goo, no dust, etc.

  • cap C203 cannot be salvaged, it is blown and broken in two pieces

  • one pad of C203 is gone sad. I can hopefiully use the nearby via to get a connection

Apart from instresting speculation about what happended to this mobo I really need advice on the type of cap that C203 was and if it could be replaced simply by a solder bridge.

This is how the top side looks:
2015-07-07%2013.26.31.jpg

TIA, bobo68

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#4 2015-07-07 13:30:48

uniserver
Member
From: Sf, Mi
Registered: 2014-05-15
Posts: 956
Website

Re: Quadra 650 does not start up - capacitor blown and a bit of mystery

Oh yes sorry about that. You're absolutely correct.


#I Re-Cap √Mac √NeTX √Amiga Boards - A/B - PSU# (MacCaps.com)  Modern SCSI HD's - For Old Macs - Pre Cfg'd - 10k RPM! 73gb!! $50 + free shipping  -- Mac 128K Re-Ram kits (16 Chips) $35 + shipping, Floppy Issues?-> Bourns Filter Solution 128k - SE/30, $16 + shipping

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#5 2015-07-07 13:39:26

uniserver
Member
From: Sf, Mi
Registered: 2014-05-15
Posts: 956
Website

Re: Quadra 650 does not start up - capacitor blown and a bit of mystery

Well there was that C650 link that I sent you, looked like it was pretty cheap.

I think you do have yourself a slight mystery on your hands here.

Of course it's hard to say what the value of that Is,  looks to me like C202 would be of the same value
Maybe remove that one and see what it's value is with the meter .

You said there was a residue like some Coke was  spilt on it .   Maybe there was .
And they just kind of half assed clean it up for An eBay sale.
Kind of a shame that people do crap like that but ...


#I Re-Cap √Mac √NeTX √Amiga Boards - A/B - PSU# (MacCaps.com)  Modern SCSI HD's - For Old Macs - Pre Cfg'd - 10k RPM! 73gb!! $50 + free shipping  -- Mac 128K Re-Ram kits (16 Chips) $35 + shipping, Floppy Issues?-> Bourns Filter Solution 128k - SE/30, $16 + shipping

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#6 2015-07-07 13:39:58

bobo68
Member
From: Germany
Registered: 2015-07-07
Posts: 22

Re: Quadra 650 does not start up - capacitor blown and a bit of mystery

If only I would hear that more often from my wife... wink

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#7 2015-07-07 13:47:29

uniserver
Member
From: Sf, Mi
Registered: 2014-05-15
Posts: 956
Website

Re: Quadra 650 does not start up - capacitor blown and a bit of mystery

Also you may want to remove and test some of those tantalum capacitors ,  techknight,  was telling me that he finds tantalums bad on boards, and sometimes they don't even look bad .


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#8 2015-07-08 02:00:48

techknight
Member
Registered: 2014-05-22
Posts: 449

Re: Quadra 650 does not start up - capacitor blown and a bit of mystery

dont blob it over, youll blow it up even more.

its an 0.1UF bypass capacitor. The question is, why did it blow? Either the cap shorted, or that rail got a very high voltage spike, which will blow the capacitor, and a large number of other ICs on there as well.

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#9 2015-07-08 07:55:21

bobo68
Member
From: Germany
Registered: 2015-07-07
Posts: 22

Re: Quadra 650 does not start up - capacitor blown and a bit of mystery

Techknight, with "don't blob it over" you mean I shall not just make a solder bridge, rigth?

About the reasons for this damage I'm still speculating. I do not think that somebody pressed down the board so much that the cap touched the metal housing. It is not far away from two spacers, so this would require a good amount of pressure. But then there is the drive power connector right on the other side of the mobo, so if someone plugged that in while the machine ran...

Thanks.

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#10 2015-08-05 12:56:51

bobo68
Member
From: Germany
Registered: 2015-07-07
Posts: 22

Re: Quadra 650 does not start up - capacitor blown and a bit of mystery

Found some time today to try again.

When I removed the burned cap C203 I saw quite a crater below it:
2015-08-05%2012.14.17.jpg

I replaced C203 by a 0.1 uF 50V cap. I had to replace the lost pad with a short wire to the via:
2015-08-05%2013.35.42.jpg

Installed the PSU - nothing. sad

I again tested the PSU outside the Quadra. It powers up and delivers voltages when I short pin 9 and 10.
I then tried to power up the PSU when it is installed inside the Quadra by shorting pin 9 and 10 - nothing.
One interesting thing: when the PSU is just connected to the mobo of the Quadra, pin 10 of the PSU goes down to 1,7 V (should be 5V). 1,7 V is probably not enough to power up the PSU completely by shorting it to pin 9.
I then supplied 5 V to pin 9 of the Quadra's PSU with my benchtop PSU - nothing. BTW this did also not work work when the Quadra's PSU was outside the Quadra. I thought supplying 5V top pin 9 would power it up but that does only work if I use the 5 V of pin 10 of the PSU for it.

So far, so bad.

I then tried to measure connectivity a bit on the mobo near the PSU connector:
2015-08-05%2013.55.14.jpg

All in all that was inconclusive to me. I guess I need a schematic.

It seems that pin 10 of the PSU is connected to plus side of C41. It then seems to go from C41 minus to C42 minus and also C202 on the backside of the mobo. If I measure resistance across C41 it shows 180 Ohms. Across C42 is practically a short. C2 looks good but that should not be the case, should it? Measuring capcitance yields nothing conclusive probably because the C's are installed.

That's where I am now. If someone has a good idea and/or a schematic that would be nice.

Best, bobo68

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