Imac 614-0378 repair advice

[villiam]

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 replacements for the fuse and rectifier but the mov is a mystery to google. It's markings are TVR 417 644.

Closest I found are these -

.

The part looks a lot like the smallest of these but the code does not match with this range. My question is, can I just leave this MOV out of the circuit, and if, with luck, it runs again with a new fuse and rectifier, choose an appropriate replacement by measuring the voltage at its position in the circuit?

Also live and neutral appear to have been swapped at the (keyed) connector between PSU and AC inlet. Should I leave this as is or swap it round?

[budm]

Re: Imac 614-0378 repair advice

You can leave MOV out for testing the rest of the power supply, They usually have MOV across Line and Neutral to clamp down the spike in the AC line.
They will usually use the MOV rated voltage at about 20% above the operating line Voltage.
They more likely use 10mm Diameter for MOV in your power supply, the bigger the diameter the higher Joules rating.

[villiam]

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 to do something on the output side to make the supply switch on without the computer connected?

Also, how would you suggest testing if the rest of the computer has survived. This PSU seems to only output two 12V rails to the DC-DC board with some kind of control signal returning on the brown wire. Is it wise to just connect up another 12v source to this and see if the rest of the computer is alive?

[ben7]

Re: Imac 614-0378 repair advice

You can replace the bridge rectifier and the varistor. There seems to be only inductors or low value resistors in the current path of the varistor, so they should be fine.

The TVR 471 is a 300VAC/385VDC (DC in this case, its after the rectifier) metal oxide varistor, tripping point is about 470v. Its maximum permissible surge power is 30J.

[villiam]

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 is biggest available in a part that will fit back in the space?

I double checked and live and neutral are swapped at the PSU connector. On the PSU a brown wire connects to the point marked L and connects to the fuse on the PCB. This connector only fits one way onto the cable to the AC inlet. The brown wire from PSU connects to blue wire at this connector and on to neutral pin of the plug. So the live from the plug is not fused at the PCB. What would you make of this?

[ben7]

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 is biggest available in a part that will fit back in the space?

I double checked and live and neutral are swapped at the PSU connector. On the PSU a brown wire connects to the point marked L and connects to the fuse on the PCB. This connector only fits one way onto the cable to the AC inlet. The brown wire from PSU connects to blue wire at this connector and on to neutral pin of the plug. So the live from the plug is not fused at the PCB. What would you make of this?

This should be good. BUT you will have to check to see if you have 7mm of space to fit the MOV in there.

The TVR471 does have a clamping voltage of 775v.

Did you find a replacement for the bridge rectifier yet?

[villiam]

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? -

http://uk.mouser.com/Search/ProductD...7-D2SBA60-7000

[ben7]

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? -

http://uk.mouser.com/Search/ProductD...7-D2SBA60-7000

Yes I think you can.

Did you measure the amount a space there is for the new varistor?

[selldoor]

Re: Imac 614-0378 repair advice

If the 7mm is too big, acccording to the Thinking TVR Series datasheet

A TVR 05 (Size) 471 (Varistor Voltage) is rated at 300Vac
385Vdc Clamping 810V Max Energy 15J

I think at mouser this would be a good equivalent
660-NVD05UCD470
http://uk.mouser.com/ProductDetail/K...2mm8QaGH0Rc%3d

[budm]

Re: Imac 614-0378 repair advice

"It's markings are TVR 417 644"
Is it 417 or 471?

[selldoor]

Re: Imac 614-0378 repair advice

"It's markings are TVR 417 644"
Is it 417 or 471?

471 -there is a picture of it.

[ben7]

Re: Imac 614-0378 repair advice

"It's markings are TVR 417 644"
Is it 417 or 471?

Its 471, he made a typo.
Look in the picture he supplied if your not sure

[budm]

Re: Imac 614-0378 repair advice

I just go by as posted since I did not see any correction on the comments by villiam after that post, sorry.

[ben7]

Re: Imac 614-0378 repair advice

471 -there is a picture of it.

Heh lol you beat me to it xD

[villiam]

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.

[ben7]

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.

You can replace the caps if you really want to, if any of them are faulty, most likely it would be the big 150uF 420v cap.

Can you tell us who the MFG of the cap is?

[villiam]

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"

[selldoor]

Re: Imac 614-0378 repair advice

Hi - these are all Ltec caps which are not considered great.

I will attach datasheets

[ben7]

Re: Imac 614-0378 repair advice

Hi - these are all Ltec caps which are not considered great.

I will attach datasheets

LOL 420v caps aren't mentioned on the TY series datasheest!

[villiam]

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?