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First One - mosfet amplifier module
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Old 14th August 2018, 09:15 AM   #4271
J.M.K is offline J.M.K  France
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Default Fried resistor on my FO 1.4M board

OK, I finally decided to examine the board with a powerful magnifier,
and dicovered that - near the input, where the problem is likely to be situated, the R6 SMD (marked 47R0) is half exploded.
Checked with my DMM : no doubt, broken resistor, when on the other side the symetrical R5 is perfectly OK.

Is it possible that R6 worked as a fuse and merely exploded because of some over current.
The close other SMDs seem to be OK (C12, T4 & T2), not sure for the tiny tracks though.

I think it's worth it trying to fix this, and see if the module is OK.
As I don't know much on this type of resistor, would you give me some reference ?

Do you think, given this brokjen R, that more damage happened further away ?

Thanks a lot for your help and patience (which I admit I lack of, most of the time) ........

JMK
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Old 14th August 2018, 03:13 PM   #4272
J.M.K is offline J.M.K  France
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Quote:
Originally Posted by J.M.K View Post
OK, I finally decided to examine the board with a powerful magnifier,
and dicovered that - near the input, where the problem is likely to be situated, the R6 SMD (marked 47R0) is half exploded.
Checked with my DMM : no doubt, broken resistor, when on the other side the symetrical R5 is perfectly OK.

Is it possible that R6 worked as a fuse and merely exploded because of some over current.
The close other SMDs seem to be OK (C12, T4 & T2), not sure for the tiny tracks though.

I think it's worth it trying to fix this, and see if the module is OK.
As I don't know much on this type of resistor, would you give me some reference ?

Do you think, given this brokjen R, that more damage happened further away ?

Thanks a lot for your help and patience (which I admit I lack of, most of the time) ........

JMK
OK, I finally removed the exploded R - actually broken in the middle.
Unfortunately, the bases to solder the SMD R on the board are also fried and gone, but I managed to trace their ends: one is to the row of next resistors, the other end is one of the legs of the T4 transistor.
I guess I'll try to replace that SMD with a discrete 47R and see what happens.

JMK
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Old 16th August 2018, 01:24 PM   #4273
J.M.K is offline J.M.K  France
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Quote:
Originally Posted by J.M.K View Post
OK, I finally removed the exploded R - actually broken in the middle.
Unfortunately, the bases to solder the SMD R on the board are also fried and gone, but I managed to trace their ends: one is to the row of next resistors, the other end is one of the legs of the T4 transistor.
I guess I'll try to replace that SMD with a discrete 47R and see what happens.

JMK
Next step : I managed (delicate surgery) to replace that blown 47R with another one.
Guess what, it's blown again immediately.
The problem is somewhere else, but I won't try to find it,
merely hoping we'll one day be able to get replacement moduiles.

Cheers

JMK
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Old 16th August 2018, 01:34 PM   #4274
Bassivus is offline Bassivus  Serbia
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Quote:
Originally Posted by J.M.K View Post
Next step : I managed (delicate surgery) to replace that blown 47R with another one.
Guess what, it's blown again immediately.
The problem is somewhere else, but I won't try to find it,
merely hoping we'll one day be able to get replacement moduiles.

Cheers

JMK
Sorry to her that... I'm also hoping for replacement soon
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Old Yesterday, 11:59 AM   #4275
Tournesol is offline Tournesol  Belgium
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For all the people who had problems with fried modules, may-be you should be interested with this protection circuit:
An ultimate amp protection circuit ?
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Tryphon Tournesol
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Old Yesterday, 12:20 PM   #4276
analog_sa is online now analog_sa  Europe
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First One - mosfet amplifier module
Quote:
Originally Posted by Tournesol View Post
For all the people who had problems with fried modules, may-be you should be interested with this protection circuit:
An ultimate amp protection circuit ?
And how would that help? Not familiar with the new modules, but the 1.2 were generally intolerant of this type of user error. As the resistors in the output Zobel have insufficient power rating, the spike the insertion of a live RCA cinch causes takes the Zobel out, the amp oscillates and often fries a tweeter. Perhaps a sophisticated protection circuit would work, but not something which only monitors dc. And the transparency of the amp will be greatly reduced by the relay.

The blown 47R resistors JMK observed are part of the NFB network. Those resistors used to also be underrated. Blowing with no signal means there is dc at output, so semis blown as well.
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