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dead sony (actually sanyo STK4231II) power amp

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landwerlen

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i have a sony LBT D550 stereo/CD player that quit working correctly after getting wet....at first it would function great after about 5-10 minutes warmup..now nothing.....my inlaws have the same unit, and i swapped out the power amp module, and was rewarded with a perfectly functioning unit....i ordered the 4231 from MCM.....and the unit worked for awhile, but has since failed again

i downloaded a data sheet on the 4231, and have begun troubleshooting.......im not an expert in this field, but a quick study.....Vcc is a whopping 124VDC (the data sheet calls +-75V the max), but i want to make sure im measuring this correctly..any help would be appreciated

im getting left and right audio from the volume control (as viewed on my scope on pins 3 and 20)

there is also a mute feature that i havent looked into yet (pin 8)

the data sheet can be found @ http://www.datadart.com/al/sanyo/STK4231II.PDF

thanks in advace
 

landwerlen

New Member
im an idiot

before anyone makes fun of me..i will.....i understand now that +-75V for Vcc is reference ground (not reference each other).....so im good there 62.3 volts+-.......back to the drawing board
 

landwerlen

New Member
yes i have..it seems very clean.....its a small board (3x5)...and ive cleaned it with contact cleaner....no obvious visual damage....john
 

landwerlen

New Member
where are all of the experts? i was hoping for more response than this.....i hate thinking about taking this stereo to a shop, when a 4 dollar transistor is the only thing keeping me from a satifactory repair.....thanks again
 

olly_k

Member
where are all of the experts? i was hoping for more response than this.....i hate thinking about taking this stereo to a shop, when a 4 dollar transistor is the only thing keeping me from a satifactory repair.....thanks again
Listen, knowone is helping 'any further' because we arn't mind readers and there could be anything wrong with your amp. It is most likely you have overlooked the obvious or there is another component taking out the power amp ic. It could just be the mute line stuck or a handful of components bust. A service manual is what you need to go any further.
People go out of there way to offer help and advice on these forums and just expect a bit of curtosy back, but given very little info there is not much anyone can do.
 

landwerlen

New Member
well the obvious hasn't been overlooked..but the mute feature is a possibility....it is connected to pin eight on the 4231 (see previous post for data sheet).....would disconnecting that prove anything? those are the kind of things that would be helpful to me......i in no way implied this forum would give a 'specific fix', but guide me by asking questions on things to check for..thanks
 

mozikluv

New Member
trouble shooting the STK4231

:?: i know how it feels when you think you have repaired the unit after installing the new one, it works for a while then it goes bonkers again.
heres my suggested areas to check:
1. have you check the muting circuit specially the diode?
2. have you check the thermal shutdown circuit transistor with a posister connected from emitter to base?
3. have you check the protection circuitry employing four (4) transistors and two (2) diodes?
i hope this would help you find the problem. happy checking! :D
 
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