# Alpine MRV-1005



## g3ngst3r (May 13, 2017)

Hello guys, recently i got this amp from a firend. The amp is working(sort of), the problem is i can only turn it on if I apply power to B+ and Remote at the same time. This way it works ok, drawing around 1.3-1.1A in idle, and producing music. But if i disconnect remote and now reconnect, the amp will draw 35mA and the powersupply wont turn on although the amps powerLED comes on. On further investigation i realised somebody has changed q802 which is a biased transistor in the B+ Switch circuit to some sort of random SMD transistor, without chechking the voltage divider before it..(the voltage divider had one open resistor the 3.6k one, which i changed now)

Could you guys give me some directions to start from? Im testing off a lab supply, and iv got pretty professional gear(student at an electrotechnics university). I actually set the power rails as described in the manual, but i could not set the idle since it says i should read 3+-1mV but i read 90V between the test points given so i dont really understand this but hey.


Here is the ful lservice manual: we.tl/LdGveqXcVo
Thanks for your time and help!

Iv posted this earlier on another forum and since then iv got some thigns done so:

okay so i have realised that no matter what is up with q802 if the green LED comes on its meaning that the B+circuit is functioning correctly. So i measured some more and iv got to IC602 which had verry strange voltages. So i started chechking and i got to pin4 which had 5 volts to it(this was extremely high since it should be something like 330mV) so i checked the datasheet for that IC ( PC494C pdf, PC494C description, PC494C datasheets, PC494C view ::: ALLDATASHEET ::: ) and i saw that the number 4 leg is dead time control, which should be max 3.3 where the duty cycle is 0) So i started searching where does that 5V come from, i checked every diode and resistor where it could possibly come from and they were all fine so the last thing was a transisto(q706, overload spkr etc protection circuit) which had 5v on its collector instead of -525mV. So i desoldered that transistor. So tranny out and the amp is now working suddenly, by its remote totally fine. 

Since then i have removed q705 and put back q706 to see and the amp works but the voltage on q706s collector is around 1.5V instead of -0.5 which is not good.. Also q705 has nothing on its base, like 1.5milivolts.. Can somebody tell me where q705 should get its base voltage please?

thanks in advance


----------

