pg ms2125 showing right clip after cap change! - diyAudio
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Old 25th May 2007, 07:39 PM   #1
marko is offline marko  United Kingdom
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Default pg ms2125 showing right clip after cap change!

just swapped the 12 input caps on my ms2125 and went to fire it up in the chassis, no speakers connected and right channel is showing clip, what have i done wrong? i've done a few of these now and all has been well, i did notice a little pop too but thought that might have just been the caps charging up, nothing is visually blown and nothing gets hot either...
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Old 26th May 2007, 11:38 AM   #2
marko is offline marko  United Kingdom
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out of the 4 rail fuses i'm getting 3@ 35volts but f4 is only showing 6volts, i'm not sure where to go from here to see why f4 is only at 6volts checked all resistors and they appear ok too!

thanks to cecil for his help so far much appreciated
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Old 26th May 2007, 01:50 PM   #3
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Are you getting 6v on BOTH sides of the fuse holder (measure at the base of the fuse holder)?

Is there a broken leg on one of the rectifiers?
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Old 26th May 2007, 01:54 PM   #4
marko is offline marko  United Kingdom
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can't see any broken legs... 6volt with the fuse out and multimeter on both sides.

i'm actually getting sound out of both channels but don't want to run the amp like this until i have 35volts on each rail, maybe it was like this before, maybe it wasn't as i never noticed the clip light on due to how the amp was mounted.
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Old 26th May 2007, 02:21 PM   #5
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Maybe one of the caps are defect (causing a kind of short circuit)
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Old 26th May 2007, 02:32 PM   #6
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Measure the voltage on the center leg of each of the rectifiers to confirm that you have 35v. If you have rail voltage on the center legs of the rectifiers, you need to follow the traces to the capacitors/fuse holders to find the break.
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Old 26th May 2007, 06:19 PM   #7
marko is offline marko  United Kingdom
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i'm sure there was 12volts on the middle legs when checked, are you talking about the input rectifiers or output ones?
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Old 26th May 2007, 07:47 PM   #8
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The rectifiers would look similar to the ones in the attached photo. Their board designation would be Dxxx. These are D304 and D305. The other side of the amp has two others but I can't read the numbers for those.

The ones with 12v on the middle legs are the power supply transistors.
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File Type: jpg p010016rect.jpg (50.1 KB, 93 views)
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Old 26th May 2007, 07:54 PM   #9
marko is offline marko  United Kingdom
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ahh, yes, the middle legs on those have slightly differant values but are the same for left and right channels, one has about 7volts and the other about 12volts iirc, no where near 35volts anyway!!

all i did to test them is put negative prob to earth and positive probe on middle leg. (all fuses in place).

edit- think i may be testing these wrong, just spotted the + and - on the rectifiers, is this where i should be putting the probes on to find 35v?
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Old 27th May 2007, 05:55 AM   #10
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Your referencing your measurements to the wrong ground point. Try using the RCA shield as the ground point for all your measurements. On this amp that is acceptable and should give the same reading as the center tap of the power toroid.

Also if you read the voltage from both of the center legs of the big power diodes, sink mounted near the big blue caps. These will give you a 70 to 72 volt reading, across those two terminals, Negative probe to one, and positive probe to the other will give you a total combined rail supply reading or twice 35 to 36 volts DC.

Recheck your fuses as measured against the RCA shield as your ground and tell us what your getting.

There is a 6 volt reading possible on this amp, IF you read across the rail and raw voltage circuits. This is also the the same circuits that those two clip transistors I sent you in pictures reside in, and the one circled in white likes to fail from abuse, and you get a constant clip indication while the amp still plays fine.

I just fixed this for Nico Boom on his 2250, so its real fresh in my mind . So re test those voltages with you negative voltmeter probe attached to the RCA shield ground please, and let us know what you get

See ya back on Phoenix Phorum C
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