HELP needed

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cobology

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Joined 2009
hi all just changed all output and input transistors on my alpine mrd-605 but still no output what else could i try i only have a DDM at hand just wondering what i could be missing out ,must be something stupid as it powers up with no warnings or faults on the amps display
 
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cobology

Member
Joined 2009
Hi thanks for your reply there is power going to output transistors and input as for the op amp not sure where these are sorry but im just starting out on this stuff gotta start somewhere i suppose here is a link to the insides of the amp could you point me as to where they are thanks so far!! and yea it is the MRD-M605 sorry missed the (M)

http://ampguts.realmofexcursion.com/Alpine_MRD-M605/
 
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jol50

Member
Joined 2007
On the bottom of the board between the RCA and fuse holder, those three 8 leg ICs in a row are likely op amps. Get the number off them and look up the datasheet. They should have the +/- 15v on them, often the end legs have the power the sheet will show you. The ICs like that for the amp section will run off the 15v, amp no work without. Seems like the display would run off it too but not sure. Ground to center tap for that like for rail voltage test.
 
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cobology

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Joined 2009
hi ok i have just sorted the power supply was giving too much power out sitting steady now at 13.6v - 13.8v so should there be power on all legs of the FETS or are they fine, also just put the dmm test leads on the speaker terminals and get a reading of around 5v drops to zero in stages then back up to 5v again within a couple of seconds in a constant loop
 
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Perry Babin

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Joined 2003
bcae1.com
For most amps, the power supply FETs will generally have from 1-5v DC on leg 1 (when measured with a multimeter - but the readings vary significantly from one multimeter to another). Leg 2 will have the same as the voltage on the B+ terminal. The 3rd leg will have 0.0v.

Do you get 5v on all channels or only on one channel? Measure the voltage directly from the terminals for the individual channels.
 
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cobology

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Joined 2009
hi yes that was measuring directly accross the speaker terminals both where the actual speaker wires screw into the amp and the speaker block terminals on the actual board ,as for the ic you mention the only one i can find with "75" in is this one here LC75421 it has got like a blue plastic coating on the legs of it here is a link for it, its just above the phono plugs to the right

http://ampguts.realmofexcursion.com/Alpine_MRD-M605/inside6.jpg

thanks for all your patience and help i would just like to get this amp working as it has a good sound and would also like to learn aswell
 
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Perry Babin

Member
Joined 2003
bcae1.com
Yes, these are the drivers for the outputs.

Is pin 2 of either of these ICs directly connected to the negative speaker terminal?

Is pin 2 of either of these ICs directly connected to the chassis ground terminal?

Are any of the speaker terminals directly connected to the RCA shield?

By 'directly connected', I mean 0 ohms or very near 0 ohms.

What are the other ICs to the left of the driver ICs in the ampguts photo?
 
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cobology

Member
Joined 2009
ok i'll start with the driver ic's from chassis ground meter reads 215 ohms and from speaker negative reads 522ohms so dont think they are directly connected ? speaker terminals to rca shield meter shows as if no connection as if leads are apart.
ok now the other ic's working away from the driver ic's are:4081BF the other two are the same ic's, 4069UBF and are fitted mirror image to each other, also driver ic's pin 2's go to the output transistors
 
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