Hi guys,
If you have a spare minute, please help a college student. I have been upgrading my aging Hi-Fi stereo with by replacing capacitors. It all went smoothly and I got nice results so I decided to replace all capacitors and the only ones that were left before it went BOOM were the caps on the amp board. The moment I turned on the stereo after upgrading amp caps and for a split second I heard a pop/crack/buzz but I continued to listen, it sounded great for 30 secs and suddenly the there was huge BOOM/bass almost sounded like my speakers exploded. I checked back and noticed wrong polarity on one 22uF cap on the amp board. I corrected the polarity and soldered the brand new one but still the stereo doesn't give off any sound, it's dead silent. I already replaced the STK4231II stereo amp/chip with brand new one and still no sound. I also replaced the AC->DC diode on the amp board, still no sound. What I noticed is that the stereo doesn't make a tick sound like it always did when it was turned on or off. I think relay makes the ticking sound, could it somehow get fried?
Here's the amp board:
^ Notice the blue building in the upper middle, that's where the relay (OEG OSA-SS-224DM3M) & big resistor is, and the L R speaker outputs.
General view:
Pre-amp and microprocessor:
^ There's one bipolar red blackgate capacitor in the middle-left, on top of that is the pre-amp area. In the middle is the NEC microprocessor, apparently it's a DAC.
Now the backsite, the NEC microprocessor is to the left, and NEC pre-amp is to the right, in the middle is a Mitsubishi opamp:
I'm no expert, I throughly checked all aluminum caps with a multimeter and they all charge and discharge properly, also there are no blown caps. I'm suspecting there's a problem with the relay because the stereo doesn't tick anymore. Also if you notice, out from the transformer there are two AC power lines, one to the amp board, one to the main board. The stereo turns on fine, It spins a CD, I see the wave animation on the display/LCD screen (that confirms that opamp, pre-amp & dac works), it's seems just like it's muted. The STK4231II stereo amp/chip isn't warm to touch it like it used to be.
Please help, I would like to listen to music again, I don't have much time and knowledge debugging circuits
.
If you have a spare minute, please help a college student. I have been upgrading my aging Hi-Fi stereo with by replacing capacitors. It all went smoothly and I got nice results so I decided to replace all capacitors and the only ones that were left before it went BOOM were the caps on the amp board. The moment I turned on the stereo after upgrading amp caps and for a split second I heard a pop/crack/buzz but I continued to listen, it sounded great for 30 secs and suddenly the there was huge BOOM/bass almost sounded like my speakers exploded. I checked back and noticed wrong polarity on one 22uF cap on the amp board. I corrected the polarity and soldered the brand new one but still the stereo doesn't give off any sound, it's dead silent. I already replaced the STK4231II stereo amp/chip with brand new one and still no sound. I also replaced the AC->DC diode on the amp board, still no sound. What I noticed is that the stereo doesn't make a tick sound like it always did when it was turned on or off. I think relay makes the ticking sound, could it somehow get fried?
Here's the amp board:
An externally hosted image should be here but it was not working when we last tested it.
^ Notice the blue building in the upper middle, that's where the relay (OEG OSA-SS-224DM3M) & big resistor is, and the L R speaker outputs.
General view:
An externally hosted image should be here but it was not working when we last tested it.
Pre-amp and microprocessor:
An externally hosted image should be here but it was not working when we last tested it.
^ There's one bipolar red blackgate capacitor in the middle-left, on top of that is the pre-amp area. In the middle is the NEC microprocessor, apparently it's a DAC.
Now the backsite, the NEC microprocessor is to the left, and NEC pre-amp is to the right, in the middle is a Mitsubishi opamp:
An externally hosted image should be here but it was not working when we last tested it.
I'm no expert, I throughly checked all aluminum caps with a multimeter and they all charge and discharge properly, also there are no blown caps. I'm suspecting there's a problem with the relay because the stereo doesn't tick anymore. Also if you notice, out from the transformer there are two AC power lines, one to the amp board, one to the main board. The stereo turns on fine, It spins a CD, I see the wave animation on the display/LCD screen (that confirms that opamp, pre-amp & dac works), it's seems just like it's muted. The STK4231II stereo amp/chip isn't warm to touch it like it used to be.
Please help, I would like to listen to music again, I don't have much time and knowledge debugging circuits
.
Hi QSerraTico_Tico,
Thanks for the help, one of the grey-blue resistor was busted, along with 4 other resistors. The IC is still isn't warm to touch and makes no sound, no tick at startup either. The caps, diodes, and resistors seem to be good on the amp board, the only thing I'm not certain are the 2 3-leg transistors/mosfets:
Here's a better shot of the relay and protector IC NEC 1237HA:
Any idea which part made a tick sound when my stereo used to work? What initiates STK4231II startup?
Thanks.
Thanks for the help, one of the grey-blue resistor was busted, along with 4 other resistors. The IC is still isn't warm to touch and makes no sound, no tick at startup either. The caps, diodes, and resistors seem to be good on the amp board, the only thing I'm not certain are the 2 3-leg transistors/mosfets:
An externally hosted image should be here but it was not working when we last tested it.
Here's a better shot of the relay and protector IC NEC 1237HA:
An externally hosted image should be here but it was not working when we last tested it.
Any idea which part made a tick sound when my stereo used to work? What initiates STK4231II startup?
Thanks.
Re: my aging Hi-Fi stereo
At least it's not all glue and sellotape like some.
Deary me !! I have worked on hundreds of units like this. You have to accept that it was working, you got enthusiastic, now it's pancaked.
The relay almost certainly connects the PSU to the amp board.
You need to go back to basics, if you have no circuit get the data sheet for the STK and trace the supplies to it. See what drives the relay coil. See if the relay coil driver transistor is being turned on and off correctly from the micro. It's all basic faultfinding, don't assume anything !! For the output stage to work it needs power. Trace it back !! And remember that you need to find what you did wrong in the first place -- or it will do it again. All good fun. When you check resistors make sure you check them out of circuit. Any residual voltage ( a few mv ) across one is enough to totally confuse a DVM on ohms.
Edit, Any fuses or safety resistors on the upturned PCB on the transformer. I see re reading it all you put a cap in backwards -- good luck, 20 mins tops to fix it then.
AndrewT said:
At least it's not all glue and sellotape like some.Deary me !! I have worked on hundreds of units like this. You have to accept that it was working, you got enthusiastic, now it's pancaked.
The relay almost certainly connects the PSU to the amp board.
You need to go back to basics, if you have no circuit get the data sheet for the STK and trace the supplies to it. See what drives the relay coil. See if the relay coil driver transistor is being turned on and off correctly from the micro. It's all basic faultfinding, don't assume anything !! For the output stage to work it needs power. Trace it back !! And remember that you need to find what you did wrong in the first place -- or it will do it again.
All good fun. When you check resistors make sure you check them out of circuit. Any residual voltage ( a few mv ) across one is enough to totally confuse a DVM on ohms.Edit, Any fuses or safety resistors on the upturned PCB on the transformer. I see re reading it all you put a cap in backwards -- good luck, 20 mins tops to fix it then.
jitter, AndrewT, Mooly, thanks for taking your time .
This is a very nice stereo with great columns, if it wasn't I would be fixing it or upgrading caps in the first place.
I'm 100% sure that the fuse and resistors on the transformer PCB board are OK. The datatsheet for the STK blows. It's either the relay or the NEC IC protector that is busted. Any idea where I could find the equivalent replacement part for the OEG OSA-SS-224DM3M (5A 50VAC 3A 125VAC 3A 30VDC) relay since these are not sold anymore?
Thanks guys.
.This is a very nice stereo with great columns, if it wasn't I would be fixing it or upgrading caps in the first place.
I'm 100% sure that the fuse and resistors on the transformer PCB board are OK. The datatsheet for the STK blows. It's either the relay or the NEC IC protector that is busted. Any idea where I could find the equivalent replacement part for the OEG OSA-SS-224DM3M (5A 50VAC 3A 125VAC 3A 30VDC) relay since these are not sold anymore?
Thanks guys
.
Unless the relay contacts have welded together ..... Check it out ?? We don't guess here Is there voltage across the coil ? If yes, are the contacts closed. If no voltage across coil trace the relay drive back !
Just looking at the picture I may be wrong saying that that relay switches the power to the amp PCB. It location on the PCB looks to near the speaker outlets, but that changes nothing fault finding wise .
What's this NEC IC protector ? IC protectors are 2 legged devices usually marked something like N10 which means -- bizzarely 10 * 40 to give the value in milliamps, so that would be a 400ma protector. It should read short if it's OK.
The power amp PCB. When you switch on is there AC voltage across the bridge rectifier middle pins ? If no, trace the connections back. If yes does the STK have the correct supplies to it. For example -/+ 22 volts or whatever it is.
Is there voltage across the coil ? If yes, are the contacts closed. If no voltage across coil trace the relay drive back !Just looking at the picture I may be wrong saying that that relay switches the power to the amp PCB. It location on the PCB looks to near the speaker outlets, but that changes nothing fault finding wise .
What's this NEC IC protector ? IC protectors are 2 legged devices usually marked something like N10 which means -- bizzarely 10 * 40 to give the value in milliamps, so that would be a 400ma protector. It should read short if it's OK.
The power amp PCB. When you switch on is there AC voltage across the bridge rectifier middle pins ? If no, trace the connections back. If yes does the STK have the correct supplies to it. For example -/+ 22 volts or whatever it is.
I have no experience with this particular box, so I may be wrong about this, but typically those relays are there to protect the speakers should the power amp go bad and put out a big DC voltage (speakers really don't like DC). The relay would be in series with the speaker contacts in that case, so as to disconnect amp from speakers.
If so, t is very unlikely that the problem would be the relay itself (particularly if you were replacing capacitors before it went). It's more likely that, were you to measure with a DVM and with the amp on, you'd find a DC level on the "amp side" of the open relay contacts and that the relay and protect circuit was doing its job of preventing your woofer voice coil from igniting.
It's even possible that the problem could be not in the power amp itself, but in the circuit driving it (if the PA is a type able to pass DC from in to out). But more likely, one of the (non main) power supply voltages that feeds the PA or earlier circuitry was blown out (a transistor or IC regulator probably) by the backwards cap, and that is upsetting things. If you haven't already tried, I'd first ascertain whether there is DC on the amp side of the relay contacts (make sure you are on the contacts, not the actuator coil pins), so you know whether this is what you are trying to debug.
Also, check for voltage (when unit is turned on) across that cap that was previously backwards -- if there is none now, I'd start there, to see where the voltage was supposed to come from. But in either case, keep in mind that you may have more than one problem now, parts failure (or misconnection) can take out more than just one or two things.
If so, t is very unlikely that the problem would be the relay itself (particularly if you were replacing capacitors before it went). It's more likely that, were you to measure with a DVM and with the amp on, you'd find a DC level on the "amp side" of the open relay contacts and that the relay and protect circuit was doing its job of preventing your woofer voice coil from igniting.
It's even possible that the problem could be not in the power amp itself, but in the circuit driving it (if the PA is a type able to pass DC from in to out). But more likely, one of the (non main) power supply voltages that feeds the PA or earlier circuitry was blown out (a transistor or IC regulator probably) by the backwards cap, and that is upsetting things. If you haven't already tried, I'd first ascertain whether there is DC on the amp side of the relay contacts (make sure you are on the contacts, not the actuator coil pins), so you know whether this is what you are trying to debug.
Also, check for voltage (when unit is turned on) across that cap that was previously backwards -- if there is none now, I'd start there, to see where the voltage was supposed to come from. But in either case, keep in mind that you may have more than one problem now, parts failure (or misconnection) can take out more than just one or two things.
Hi,
The bridge rectifier has been replaced before starting this thread, you can see how I bend the legs.
There's ~53.5v across the DC filtering caps, and 5.0v where the backward 22uF was.
The same ~53.5v goes through 2 of the legs of the blue relay. Here's a datasheet for the interesting IC protector: http://pdf1.alldatasheet.com/datasheet-pdf/view/6670/NEC/C1237HA.html
The bridge rectifier has been replaced before starting this thread, you can see how I bend the legs
.There's ~53.5v across the DC filtering caps, and 5.0v where the backward 22uF was.
The same ~53.5v goes through 2 of the legs of the blue relay. Here's a datasheet for the interesting IC protector: http://pdf1.alldatasheet.com/datasheet-pdf/view/6670/NEC/C1237HA.html
The "typical application" schematic on the 3rd page shows the device using the relay to disconect the speakers. If you have 53.5V on the pins that go to the speaker, and it's getting through, that would be a very bad thing. Are you sure the voltages from those 2 pins is going *through*, and isn"t just a huge DC level from the power amplifier showing up on both channels (and being blocked from passing by the relay)? Or that they aren't the two pins of the relay coil (schematic shows big voltage on one end of the coil, other getting pulled down by the chip to activate the relay -- if not activated, that voltage would appear on both coil pins of the relay).
Assuming they are using the chip in the way shown in the typical application (they might've gotten more creative).
Can you get to pins 12 or 15 of the STK4231 when the box is powered up? If so, look at the DC voltage from there to the chassis. Should be very near zero volts.
Also check pins 13 and 14 (should be highish positive voltages) and pin 11 and 16 (should be highish negative voltage, about the same amount negative as pin 13 is positive.
http://pdf1.alldatasheet.com/datasheet-pdf/view/41609/SANYO/STK4231.html
According to the STK4231 sample app circuit there should be two resistors of about 1k ohms each going to the - lead of a capacitor (that might be the one that you had in backwards - one of the resistors goes to pin 10 of the STK4231), check those with an ohmmeter (with unit turned off). See if one isn't burned open.
Assuming they are using the chip in the way shown in the typical application (they might've gotten more creative).
Can you get to pins 12 or 15 of the STK4231 when the box is powered up? If so, look at the DC voltage from there to the chassis. Should be very near zero volts.
Also check pins 13 and 14 (should be highish positive voltages) and pin 11 and 16 (should be highish negative voltage, about the same amount negative as pin 13 is positive.
http://pdf1.alldatasheet.com/datasheet-pdf/view/41609/SANYO/STK4231.html
According to the STK4231 sample app circuit there should be two resistors of about 1k ohms each going to the - lead of a capacitor (that might be the one that you had in backwards - one of the resistors goes to pin 10 of the STK4231), check those with an ohmmeter (with unit turned off). See if one isn't burned open.
Hi bwaslo,
Thanks for checking out the datasheet. Sorry about the *through* word, I'm not certain where the voltage is flowing.
STK4231II IC:
Pin 1 : +53.6v
Pin 2 : +51.7v
Pin 3 : +5.33v
Pin 4 : +5.27v
Pin 5 : -0.010v
Pin 6 : -1.481v
Pin 7 : +51.8v
Pin 8 : -0.752v
Pin 9 : -2.016v
Pin 10 : -2.628v
Pin 11 : -53.8v
Pin 12 : +17.46v
Pin 13 : +54.2v
Pin 14 : +54.2v
Pin 15 : +0.03v
Pin 16 : +0.02v
Pin 17 : +0.01v
Blue Relay (6 pins, or 3 pairs);
(+54.2v) (-0.890v) (0.00v)
(+54.2v) (+17.32v) (0.00v)
All measurements were taken using a chassis as a ground. Something seems fishy about the pin 12 and middle pin of the relay. I'm going to take apart the stereo and continue debugging the amp board for bad resitors, caps etc once again and see which parts are connected to pin 11, 12, 16.
Thanks for checking out the datasheet. Sorry about the *through* word, I'm not certain where the voltage is flowing.
STK4231II IC:
Pin 1 : +53.6v
Pin 2 : +51.7v
Pin 3 : +5.33v
Pin 4 : +5.27v
Pin 5 : -0.010v
Pin 6 : -1.481v
Pin 7 : +51.8v
Pin 8 : -0.752v
Pin 9 : -2.016v
Pin 10 : -2.628v
Pin 11 : -53.8v
Pin 12 : +17.46v
Pin 13 : +54.2v
Pin 14 : +54.2v
Pin 15 : +0.03v
Pin 16 : +0.02v
Pin 17 : +0.01v
Blue Relay (6 pins, or 3 pairs);
(+54.2v) (-0.890v) (0.00v)
(+54.2v) (+17.32v) (0.00v)
All measurements were taken using a chassis as a ground. Something seems fishy about the pin 12 and middle pin of the relay. I'm going to take apart the stereo and continue debugging the amp board for bad resitors, caps etc once again and see which parts are connected to pin 11, 12, 16
.Pin 12 is connected to a good resistor which is connected to 1 of the leg of a transistor/mosfet (left one on the pic), tracing this path further, the middle leg of the (broken?) transistor is connected to pin 7 on the main board (labeled as OVERLOAD-DET on the pcb), which in turn connects to pin 1 of the C1237HA. Pin 16 on the STK is directly connected to (-) leg of the filtering DC cap which in turn is directly connected to the (-) leg of the rectifier, I don't understand why there was +0.02v, (I'm assuming error in the measurement).
This isn't easy at the end of a keyboard.
I would try comparing one channel against the other, and it may be worth seeing if the other channel actually works OK. That means taking the output from pin 15 to a speaker, not directly, maybe through a 100 ohm to begin with, or a cap to protect it if anything happens. Assuming thats OK it should be possible to compare then.
I would try comparing one channel against the other, and it may be worth seeing if the other channel actually works OK. That means taking the output from pin 15 to a speaker, not directly, maybe through a 100 ohm to begin with, or a cap to protect it if anything happens. Assuming thats OK it should be possible to compare then.
Pin 7 looks way wrong. Check the resistor it connects to, see if it went open. Or the one that connects to the other end of the resistor (where the cap to ground is).
Are you sure you measured pin 16 right? Should be most negative voltage in system (or there's an open trace like Mooly said).
Are you sure you measured pin 16 right? Should be most negative voltage in system (or there's an open trace like Mooly said).
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