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Old 25th April 2012, 07:14 PM   #1
srinath is offline srinath  United States
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Join Date: Feb 2010
Default stk-4151v test.

I have a yamaha rx-v870 that I believe has a bad stk 4151v chip in it. If that board is plugged in the amp never comes out of protect. If that board is un plugged the amp doesn't get any signal to make a sound but does come out of protect.
I am thinking that is the culprit, but can someone point me to where I can test it - like pin 6 and 1 should be 3.3 ohm, not 0. Like that.
Thanks.
Srinath.
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Old 26th April 2012, 03:37 AM   #2
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Location: Edmonton, AB Canada
You can check some of the STK module's transistors with a multimeter. Usually the output transistors short or open. Also look for matching multimeter readings comparing between channels.

Multimeter (+) to the first pin in list.
Meter on diode test:
Pin 13-12 and pin 13-15 open. Pin 12-11 and pin 15-16 open.

Meter on ohms:
Pin 13-2 and pin 13-21 high on ohms (I'm not sure what R9,R19 are on the chip)
Pin 2-7 and pin 17-21 some R reading (not open)

This works for STK4141,STK4151,STK4161,STK4171,STK4181,STK4191,ST K4201,STK4211 family... STK4151 datasheets pdf
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Old 26th April 2012, 06:55 AM   #3
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If both the inputs (inv and non-inv)show nearly same voltage, then the STK is good.

However if these are not near zero, then some component around the IC is the culprit.

How old is this set?

Gajanan Phadte

Last edited by gmphadte; 26th April 2012 at 06:58 AM. Reason: correction, addition
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Old 26th April 2012, 12:08 PM   #4
srinath is offline srinath  United States
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Priariemystic: I will check it with your idea.
Gmphadte: The inv and non-inv inputs, are they output of the stk - see there is like 4 connectors with 2, 3, 4 and 5 pins going to the board.
I will look on the schematic and the circuit boards and test it. It was made in the mid 90's if I am right. I am pretty sure the stk is bad, but in firther fiddling I did after I figured it was bad, I may have damaged more stuff.

Thanks.
Srinath.
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Old 9th May 2012, 06:13 AM   #5
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Late reply but still I will write.

Any amp has two inputs, the inv and non-inv. And if the total internal circuit works, these will show nearly same voltage.

Gajanan Phadte
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Old 14th May 2012, 08:13 PM   #6
srinath is offline srinath  United States
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OK I got the new stk4151V chip and swapped it in.
The amp turns on and stays on if I leave connector "CB109" - Bottom left of pic unconnected.
If I connect it it turns on and 5 sec later shuts off. From past experience it has been a transistor shorting to ground, except in this case, the stk4151 has not even been screwed into the heat sink, I have tried it off the heat sink and it still shuts off.

Unplugging or plugging in any of the other 3 has no effect. What could be going on, and I also have a stuck relay RY104 - Its stuck open, not closed. So I thought it would just not make sound, but can that cause the amp to not stay on ?

Thanks.
Srinath.
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File Type: jpg rx-v870_rear_amp.JPG (96.0 KB, 135 views)

Last edited by srinath; 14th May 2012 at 08:39 PM. Reason: Forgot attachment.
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Old 14th May 2012, 09:04 PM   #7
wahab is offline wahab  Algeria
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The STK should be mounted to the heatsink before powering on ,
otherwise they may get in a thermal runaway , dont know if there s
a protection in such a case.

As for the output relay , it is normaly open a few moments
at power on before the temporisation switch them on unless
the power module has a default , typically too high output
DC offset.
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Old 14th May 2012, 10:13 PM   #8
srinath is offline srinath  United States
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This relay is stuck I cant get the L shaped piece that is supposed to "rock" when it gets voltage to even move.
I'll test the stk - by removing it and seeing if the behavior changes.

Thanks.
Srinath.
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Old 14th May 2012, 11:25 PM   #9
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Default Try a few things

CB109 is the power connector for the STK modules. If it's unplugged, RLY104 doesn't have power and can't pull in. CB103 is to the speaker protection logic and if it's unplugged, RLY104 won't get the signal (SPR) to pull in.

With CBL109 and CBL103 in, ensure the STK's have around OV on their outputs. Otherwise, DC voltage there will go through DCDT on CBL103 and tell the protection logic to shut down.
Check R275, R268 as these look like fusible resistors.
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Old 14th May 2012, 11:38 PM   #10
srinath is offline srinath  United States
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R275 and 268 were literally on the nose for their ohm value.

The protection relay - we're not even going that far as yet, with 109 plugged in, the amp turns itself off 5 sec after you put it on.

With 109 unplugged the amp stays on, but safety relay doesn't click.

Now the RL104 is stuck, I doubt it will ever click on ... I have in fact opened relays and seen them work, or in fact not work, they are typically blown up or have burnt coils or something, however this guy is stuck, well, I am probably going to check for voltage on the coil and worry about getting a replacement.

Anyway, plug in 109 and the amp turns off.

Thanks guys.
Srinath.
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