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Old 8th May 2009, 09:10 PM   #1
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Default yamaha receiver r-300

hi all,
i joined the forum because i need some assistance in repairing a r-300 yamaha amp+receiver (acquired of course on ebay).

short description:
- receiver part is ok (i checked the output from the receiver module with a speaker - because i don't have an oscilloscope - and i got signal)
- the amp module consists of an STK3042II and STK2030.
- relay works normally
- no sound in speakers

problem:
- with a voltmeter i checked the voltage in all indicated joints in the amp module. all values are as indicated on the board except two: on the STK3042II on pin 2 i get -9V instead of -15V and on pin 14 i get +29V instead of +15V
- around the second chip (STK2030) most voltages are about +(-)35V. the chip (and heat sink) become hot.
- on the speaker output on both channels and on both A and B i also get a voltage of +35V and -35V

any tips would be appreciated. if it helps i can also post the schematics

regards,
edgar
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Old 8th May 2009, 10:29 PM   #2
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If you have rail voltage at the speaker output, usually that means the output transistors are blown. You will have to replace the STK2030s. They are available at www.tversatzteile.de.

Pins 2 and 14 of the STK3042II are the non-inverting inputs and should get the feedback signal from the STK2030's outputs. No 15 V should be present there. Once you desoldered the STK2030s, check the voltages at pins 5, 6, 10 amd 11. They should be nearly 0. If they are around 35 V, replace the STK3042II as well. They are obsolete. You can use STK3062II or STK3082II as replacements with higher voltage rating, if you find them. Don't use STK3062III or STK3082III, they are power amplifiers. Or you can try to swap in STK350, which is the follow-up, but you might have to change some capacitors to different values for stability.

It may turn out less expensive to get another amplifier from ebay, however.
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Old 9th May 2009, 05:23 PM   #3
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Default the particular amp

even in original condition dind say much soundwise anyway .
others that used similar topology ( Luxman i think ) had similar results ....

all amplifiers that are based on 30XX drive ic didnt sound ...perfect....

i know i am in the chip forum ..... but if it was my amp i would built a transistor amplifier to put inside there ( unless you are a person that likes things in original conditions )

there is a million of amps easy to bulit well documented arround the forum that will sound a gozillion times better

transistorian regards sakis
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 9th May 2009, 09:32 PM   #4
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thank you for your quick replies!

as a remark: i bought this amplifier knowing it was broken. i just wanted to use it as a little exercise. my knowledge of electronics is not much above the basics, but still i enjoy opening cases, soldering and desoldering things (perhaps you know what i mean)

i followed pacificblue's advice and desoldered the STK2030 chip. after that i measured the voltages at pins 5, 6, 10, 11 on the STK3042II and unfortunately they are around 35V.. in the next days i'll try to order the two ics.
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Old 9th May 2009, 09:32 PM   #5
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Default Re: the particular amp

Quote:
Originally posted by sakis
[...] i know i am in the chip forum ..... but if it was my amp i would built a transistor amplifier to put inside there ( unless you are a person that likes things in original conditions )

there is a million of amps easy to bulit well documented arround the forum that will sound a gozillion times better

transistorian regards sakis
a complete new transistored amp is a bit to great a challenge for me now.. maybe later..
and yes, i like things in a condition similar to the original
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Old 11th May 2009, 06:42 PM   #6
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i bought the 2 chips from ebay. they should arrive in a week..
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Old 11th May 2009, 06:46 PM   #7
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Default some things

is a question of taste and procedure ....i do things this way you do things another way ...i am very happy with that

get us some pictures when you are done

let us also know how it sounds

thanks sakis
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 15th May 2009, 01:39 PM   #8
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the chips arrived today!
before i solder them i have another (noobie) question: ia there any way i can check if the voltages on the board are right? because i wouldn't like to solder them and burn them so soon
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Old 15th May 2009, 08:31 PM   #9
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i installed the new stk2030 and stk3062II.
the first observations:
- voltages at ic's pins seem to be ok
- stk3063II seems to get warmer (only stk2030 has a heatsink)
- output volume is very very low

does anyone what the problem might be?

thanks,
edgar
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Old 15th May 2009, 09:39 PM   #10
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i take it back.. problem solved. i just discovered the amp was tape monitoring..

thanks for your help, it's working just fine now!
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