Re: Things you can find on that dead motherboard in the closet
Hi, I just recently came across these large value ceramics. I believe they are a pretty recent development intended as alternatives to some polarised electros. They are called MLCCs. Multi Layered Ceramic Capacitors. I think they top out at around 50uF 50V. They vary pretty wildly in price from small quantity price per cap of say 50p up to > 30GBP! Lots of the ones I was looking at were X7R.
villiam
Member
Last Activity: 08-26-2013, 05:27 PM
Joined: 06-23-2012
Location: Perthshire
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Re: Turn the wayback machine to 30-pin SIMMs
Hi logistics, you might find this interesting. Remember Commodore Amigas? Believe it or not a German company individual computers is producing new accelerator cards for these machines today! The CPUs run at comparable speeds to the original 80s/90s expansion cards, (~25-48 MHz), but boast ~30% performance boost due to using more modern SDRAM. Maxing out old machines is a lot of fun, if you're sick, you're not the only one.
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Re: Imac 614-0378 repair advice
Success, imac is going again. Thanks for all your advice.
Guess I got lucky and the protection parts did their job by blowing up. New fuse, MOV, rectifier and all electros replaced. Also swapped the live and neutral the right way round, urgh, that turned out to be a horrible hassle, I wish I hadn't spotted it. I very nearly botched what should have been a simple repair but at least I didn't send it out my factory door like that.
Anyway, all seems well, except now the optical drive appears to be knackered so I still can't...Leave a comment:
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Re: Imac 614-0378 repair advice
Ah, I was hoping it was testing in circuit that might have caused the funny readings. I didn't really want to desolder anything that I would have to put back in, but wanted to make sure those diodes were at least not short or open. I'll continue my optimism and assume they are fine for now.
I should have this thing back together tomorrow night, can anyone tell me how to test it without reconnecting the imac? Will it turn on with no output connected or do I have to trick it in some way?
How about testing the imac, can...Leave a comment:
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Re: Imac 614-0378 repair advice
Parts arrived the other day, so I started taking out the old caps and continuing the imac theme of "not so pretty on the inside" found a bunch more stuff crammed under the high voltage cap including, grrrrrrr, another small electrolytic. You can see it in the pic, (C21), and maybe also see the first small one I mentioned looking a bit bulgy on top, (C32). Have to wait til tomorrow before I can finish soldering.
I used a multimeter continuity/diode test on those two diodes under there. The large tested normal but I'm not sure...Leave a comment:
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MLCCs - Alternative cap choices for old computers.
Hello. I'm after some advice on whether replacing some electrolytics on a couple of old computers with MLCCs in certain places is a reasonable plan. Here are the situations -
1. Commodore Amiga A600. Audio output coupling caps are 22uF 25V SMD polarised electrolytics. However, the audio output is a bipolar signal, (so I'm told, I haven't checked yet). Lots of people are replacing them with film types and such. But I hate to put leaded components on SMD pads plus they are bulky and located in awkward spot. Any reason not to choose something like these MLCCs assuming I can find one... -
Re: Imac 614-0378 repair advice
This one shows where I think there is a problem. On my one, the ringed connector reverses blue and brown....Leave a comment:
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Re: Imac 614-0378 repair advice
No, the wiring appears correct at the board and the inlet, but the connector between the two, (which is keyed for one way only connection), is reversed so that brown->blue, and blue->brown. The PSU side of this connector is just half in the shot at the bottom left of the new photo I posted.
Sorry I can't photograph the inside of the AC inlet without dismantling virtually every thing inside the mac. I haven't seen it so I only assume it is wired correctly by continuity test from its side of the problem connector to the plug pi...Leave a comment:
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Re: Imac 614-0378 repair advice
Yes I saw that thread. I think they are talking about the brown wire on the output of the PSU which is some control from the DC-DC board. I mean the blue and brown AC input wires.
I've attached a photo, the wires are out of focus but you can see the colours under the extra sleeve. Notice the brown wire connects to the point marked L on the board and directly to the fuse F1. The problem is the connector that this plugs into has the reverse colours. So the wire from the AC inlet which connects to the point L is in fact the...Leave a comment:
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Re: Imac 614-0378 repair advice
I decided I will replace the caps. Hiding under the 420V cap, there is a 25V 68uF which looks suspect, top of the can is bulging a little.
I guess whatever happened can't have done the caps any good so might as well put in some better ones. Nichicon HE series a sensible choice for the 16V parts plus a PZ series for the high voltage cap and an HV series for the 25V 68uF? Mouser don't stock an X2 cap that will fit so I'll leave it for now.
Anyone got any thoughts on the live neutral reversed thing I described above?Leave a comment:
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Re: Imac 614-0378 repair advice
Oops, sorry for the typo. Varistor markings are TVR 471 644.
Caps are all glued down on one side only visible markings are -
150uF 420V TY105(degrees)C(M)
2200uF 16V LZG105(degrees)C(M)
1000uF 16V hang on I'll bend up this little one, looks like -
PET 6N12D (date stamp?) and a logo "LTec"Leave a comment:
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Re: Imac 614-0378 repair advice
There is a volume of approx 10x12x6mm which the old one was folded over into. This is indicated in the 4th photo (named inputb). It is an awkward spot, especially to get to the other PCB pad but I think I'll be able to get one in a bit bigger than what came out.
Do you recommend I replace all the big electrolytics after this kind of failure, they have no visible damage but . . .while I'm in here? plus, I need to order enough stuff from mouser to make it worth the postage cost.Leave a comment:
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Re: Imac 614-0378 repair advice
Great, thanks. The old one is ~6mm and was all taped up, (like maybe they knew it might explode?), I think I can get a 7mm one in the space.
The bridge rectifier is marked
D2SB
60A 60
I can replace it with this ok? -
[url]http://uk.mouser.com/Search/ProductDetail.aspx?R=D2SBA60-7000virtualkey62710000virtualkey627-D2SBA60-7000[/url]Re: Imac 614-0378 repair advice<br /...ode?), I thinkLast edited by villiam; 06-26-2012, 01:28 PM.Leave a comment:
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Re: Imac 614-0378 repair advice
Thanks ben7. I'm trying to find a suitable replacement varistor at mouser since they carry the exact model of fuse I need to replace.
I can't find one which matches the specs you have given. For example parts with DC rating of 385V have clamping voltage much higher ~700V. or parts with clamping voltage of 475V have lower voltage and energy rating.~270V DC 9J
I'm not too sure how to choose a good substitute. I guess I need DC rating a chunk above the nominal, how do I choose clamping voltage? I guess energy absorption...Leave a comment:
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Re: Imac 614-0378 repair advice
Thanks budm, I'm not sure about the position of this MOV in the circuit, it is a small disc ~5mm, doesn't seem to be directly across the line input. I've attached some photos showing the position of the damaged components I have removed. Any experienced eyes spot any other signs of trouble on this unit?
Any tips on how to proceed with the repair would be welcome, I have some electronics experience but next to none with switching supplies. My plan at the moment is just to replace the rectifier and fuse and see what happens. Do I need...Leave a comment:
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Imac 614-0378 repair advice
Greetings. I have here a workmates Imac which he described as working one night and lifeless the next day. I found some related threads here and you certainly seem to be the people to ask about this stuff.
I used some swearwords to open up the Imac, 20", 2.16Ghz Core2duo model, and found a small burn mark near the PSU. The PSU is AcBel model API4ST03 and apple P/N 614-0378.
So far I have found a blown fuse, two apparently shorted diodes in the bridge rectifier and the cause of the burn marks was an exploded MOV. There is no other obvious damage. I have found...
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