Alpine MRV-1507 - RCA Ground Floated - Need help - Page 2 - diyAudio
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Old 1st June 2008, 12:37 PM   #11
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Join Date: Oct 2007
Now ive been discovering some more faschinating voltages

The emitter voltage for Q721 is ~10 volts so it is conducting.

Very strange because Q703 base-emitter voltage is still
~0.15 Volts = not conducting...

And the supply voltade is about 12 volts on Pin 14.
But with a small pulse (can only se this on my scope not with
the DMM) Its a difference of Max 0,4 volts...

Can this be the leds causing a small voltage drop when
the leds are flashing since the pulsing is exactly the same
as the clock-pulse?
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Old 1st June 2008, 12:53 PM   #12
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Location: Louisiana
The voltage regulator for the 8v line appears to be defective. Check Q604 and ZD601.

The LED could cause a small drop but I wouldn't expect it to be enough to be visible on a scope.
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Old 1st June 2008, 01:01 PM   #13
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I tryed to remove Q721 as you said by heating
the two legs by applying solder between them
and lifting the transistor with a small tong...

But i accidently ripped of the top surface of the
transistor as i draged it lose =/

But the LED is constant Green now... so the IC is probably OK.

Maybe Q721 was leaky?...


When measuring Q703 after removing Q721...


When RCA ground not attatched no voltage on either
Base or collector, and if i clamp the RCA ground again
i got a ~5volt drop on both Base and Collector
refering to ground....

Is there some equivalent for DTA144 that i can use as i cant
find this specific modell with internall base resistor :S
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Old 1st June 2008, 01:37 PM   #14
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Location: Louisiana
The DTA144 should be readily available.

With the black lead on the ground terminal of the amp and no RCA ground, the voltage should be higher on the base of Q703 than when the RCA shield is grounded.

Q721 could have been defective.

Did you check the regulator components?
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Old 1st June 2008, 01:55 PM   #15
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no i didnt check the regulator components.
wich of them are the important ones to check?

getting a bit confused when looking at the schematic.
its a bit more complicated than the older 1505 i worked on
before

Maybe DCV on the RCA shields damaged Q721. is it possible?
Its directly attached to 2nd Ground....
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Old 1st June 2008, 02:09 PM   #16
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Location: Louisiana
Q604 and ZD601.

Low voltage on the RCAs shouldn't damage Q721. The 2nd ground is pulled up towards the 8v regulated voltage by R717 (? - difficult to read on the schematic).
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Old 1st June 2008, 02:36 PM   #17
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very hard to see indeed...

R717 11k between Q721 collector and Q703 base?

Voltages on Q604 are as it should be.

Over ZD601 i have 8.8 volts excatly as i should.

Q721 must have been defective, can you se
any other possibility?
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Old 1st June 2008, 03:39 PM   #18
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I continued with fault finding the Low batt circuit as i cant
get a new transistor before monday.

IC702 has wierd voltage readings. Within ( ) as it should be.
pin1 -11,6 (15,5)
pin2 5,3 (4,67)
pin3 6,8 (7,1)
pin4 -12,8 (-15,8)
pin5 0,2 (1,8)
pin6 16,6 (1,5mV)
pin7 16,6 (1,8)
pin8 17 (15,9)

Im starting to think that ALL OP amps and ICs are
defective, could this be the case? :S

Q702
E 0,2 (0)
C 11,3 (0)
B -11,6 (14,8)

Q720
E 0,2 (0)
C 0,3 (1,84)
B 11,3 (0)
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Old 1st June 2008, 04:19 PM   #19
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+15/ -15Volt regulator

Q619
E 16,86
C 56,4
B 17,5


Q620
E -12,7
C -51,8
B -13,3

Maybe this can cause the differential amp IC
to give at the negative voltage?

the more i dig in this amp the more trouble i get :P
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Old 1st June 2008, 06:41 PM   #20
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And a stupid question...
I am going to replace the IRFZ48N FETs...

They have blown before, and are replaced...
And when measuring them i accidently shorted two of the
legs on one of them...


So now I am going to replace them all just in case.
Was thinking of replacing them anyway because of
the +-15 Volts regulator is not giving 15 volts on
the negative side....


Can i use the IRFZ48V instead of the N modell?

Better specifications than the V modell...
And for less than half the price, can this be any good?
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