Pomegranate
Active Member
Hi everyone,
First of all, I’m fairly new to this, so please take my advice with a grain of salt. I did a few STK replacements and thought I’d share my experience with you. STKs offer surprisingly good sound quality, but are known to break easily. This is how I diagnose and replace them, based on various info I gathered on the Internet.
Tools you’ll need:
· For checking: a multimeter
· For replacing: a new STK (same model as the old one), a rectangle of solid plastic, thermal paste, soldering station, solder, desoldering wick and resin (a desoldering gun is also good)
What to consider:
· Never connect a good set of speakers to a device that may have a bad STK, because you risk destroying them. If you really must, use a cheap pair that you don’t mind breaking.
· As a rule of thumb, if a device turns on but you have no sound and it has a STK inside, this circuit is most likely faulty.
· STKs are integrated amplifier circuits made by Sanyo. They are found in low-end and mid-to-low-end audio equipment. Before attempting a repair, consider if it is worth it.
· Looking at the plastic front of the STK, pins are numbered from left to right.
· STKs come in two flavours: two-channel (amplify both channels using one component; more than 15 pins) and one-channel (one STK for each channel, less than 15 pins).
· My multimeter has an auto-adjusting range. If yours doesn’t, make sure to select the correct range.
· These instructions are only for STK power amplifiers. There are other types of STKs, like voltage amplifiers, but I don’t know how to check those.
This is a set of steps for diagnosing a bad STK in an amplifier or receiver.
1) You should start by opening the top cover and vacuuming the dust inside, if there is any. Make sure the device is unplugged.
2) Next you will need the circuit schematics to find the pin layout. Sites like alldatasheet.com are extremely useful. On this document you have to find the +Vcc pin and the output pin(s). These are always the pins that connect directly to the +Vcc and to the output, with at most a very small resistor. On this diagram of a STK 465 I circled what you should look for:
3) Look inside for the relay. If there is one, plug in the device and turn it on. Listen for the relay clicking. If it doesn’t, it most likely means there is a big voltage going to the speakers because the STK has shorted. If there is no relay, don’t connect any speakers and be careful with the speaker terminals.
4) With the device unplugged, access the pins on the underside of the PCB. If you are lucky, the bottom can be unscrewed and taken off entirely (Fisher CA-120). If you are not, you’ll have to remove the entire board and turn it over (Onkyo TX-7620). Take the multimeter and set it on ohms. Check the resistivity between +Vcc and the output pins. This should be very big, about half of a megaohm. If it is several hundred ohms or even less, there is a short.
5) Plug in the device. Be careful here! Turn on the device and set the volume knob to 0. Set the multimeter to volts. One probe goes on the metal chassis (or somewhere where is it grounded, like on the ground pin of the STK) and the other probe on the output pins of each channel. The voltage should be very low, several millivolts. If you see numbers greater than 20 V (either negative or positive), the STK is shorted. Make sure you don’t accidentally short pins with your probe!
6) Lastly, check the voltage on the speaker terminals, with the device on, the multimeter set to volts and the speaker output turned on. Make sure you have contact on the probes, the black one goes to the black terminal and the red probe to the red terminal. If the relay is not clicking, you should have a very small voltage, because the device is in protection mode. If the relay has clicked or there is none and the STK is faulty, you should see a very high voltage, greater than 20 V usually.
7) If there are two STKs inside it is also a good idea to check the channel fuses, if there are any. If a fuse is blown on a channel, this usually indicates which STK is faulty.
Now, that you made sure you have a faulty STK, this is how you replace it:
1) Before installing the new STK, you should check the resistances on it like you did with the old one. This can save you a lot of effort if the new STK is also faulty.
2) Turn off the device. Unscrew the STK from the heat sink.
3) Desolder the pins from the PCB, using the solder wick and resin (or the desoldering gun). Tip: it is best to practice first on another PCB if you are new to soldering and desoldering, because STKs have pins really close to one another.
4) Take a square of toilet paper and wipe off the thermal paste from the heat sink. You can do the same with the old STK if you plan to keep it. The paste can’t be cleaned with water, so if you get it on your fingers it is best to wipe it off with TP.
5) Apply a small amount of thermal paste on the new STK and spread it in a thin, even layer on the metal back, covering it completely. Use a solid piece of plastic with a straight edge to do this. Old credit cards work well. I’m using a rectangle of transparent plastic I cut from a lid of a Muller Cremoso yogurt.
6) Place the new STK in the device. Make sure all the pins are in their holes. I find it useful to screw it slightly, so it stays in place when soldering.
7) Solder back the pins. Be careful not to short any.
8) Now take the multimeter and set it on connection check. Verify the connection between each pin and the next component it connects to on the PCB. You want to hear a beep everytime. Now check the connection between the pins of the STK, making sure they are not shorted. Some of them should beep, like the output pins on some models that are connected together. Refer to the electrical diagram for your STK.
And this should be it. Check again the new STK like you did with the old one, making sure nothing is shorted. Also listen for the relay clicking and check the speaker terminals. I recommend listening with a pair of cheap headphones and then with a pair of cheap speakers before connecting your actual expensive speakers, to make sure the new STK works well.
You can also replace a STK with a different model, but you have to make some adjustments to the circuit. You have to research further if this is the case.
A big problem is sourcing new quality STKs, because Sanyo doesn’t make them anymore. Aliexpress is a big hit or miss. I ordered one from there, waited almost two months for it and after installing it I discovered it was also faulty. There are also eBay sellers, but you should be wary of them, too. I find it best to order from a reputable online store that also has a physical address and offers warranty. If you are from Romania, I got three STKs from electronicservice.ro. They must also be Chinese, but look very well made and all of them worked. The store is also very professional.
If you want to read more on this subject, here are a few links with very useful information:
https://audiokarma.org/forums/index.php?threads/how-to-test-stk-ics.717075/
https://www.petervis.com/electronics/stk465/stk465.html (this entire site is very good)
That’s all I have. Don’t take my exact word for it, because I’m not very experienced and some of the info may be wrong. Maybe the more knowledgeable users can point out the wrong parts and offer their own advice.
First of all, I’m fairly new to this, so please take my advice with a grain of salt. I did a few STK replacements and thought I’d share my experience with you. STKs offer surprisingly good sound quality, but are known to break easily. This is how I diagnose and replace them, based on various info I gathered on the Internet.
Tools you’ll need:
· For checking: a multimeter
· For replacing: a new STK (same model as the old one), a rectangle of solid plastic, thermal paste, soldering station, solder, desoldering wick and resin (a desoldering gun is also good)
What to consider:
· Never connect a good set of speakers to a device that may have a bad STK, because you risk destroying them. If you really must, use a cheap pair that you don’t mind breaking.
· As a rule of thumb, if a device turns on but you have no sound and it has a STK inside, this circuit is most likely faulty.
· STKs are integrated amplifier circuits made by Sanyo. They are found in low-end and mid-to-low-end audio equipment. Before attempting a repair, consider if it is worth it.
· Looking at the plastic front of the STK, pins are numbered from left to right.
· STKs come in two flavours: two-channel (amplify both channels using one component; more than 15 pins) and one-channel (one STK for each channel, less than 15 pins).
· My multimeter has an auto-adjusting range. If yours doesn’t, make sure to select the correct range.
· These instructions are only for STK power amplifiers. There are other types of STKs, like voltage amplifiers, but I don’t know how to check those.
This is a set of steps for diagnosing a bad STK in an amplifier or receiver.
1) You should start by opening the top cover and vacuuming the dust inside, if there is any. Make sure the device is unplugged.
2) Next you will need the circuit schematics to find the pin layout. Sites like alldatasheet.com are extremely useful. On this document you have to find the +Vcc pin and the output pin(s). These are always the pins that connect directly to the +Vcc and to the output, with at most a very small resistor. On this diagram of a STK 465 I circled what you should look for:
3) Look inside for the relay. If there is one, plug in the device and turn it on. Listen for the relay clicking. If it doesn’t, it most likely means there is a big voltage going to the speakers because the STK has shorted. If there is no relay, don’t connect any speakers and be careful with the speaker terminals.
4) With the device unplugged, access the pins on the underside of the PCB. If you are lucky, the bottom can be unscrewed and taken off entirely (Fisher CA-120). If you are not, you’ll have to remove the entire board and turn it over (Onkyo TX-7620). Take the multimeter and set it on ohms. Check the resistivity between +Vcc and the output pins. This should be very big, about half of a megaohm. If it is several hundred ohms or even less, there is a short.
5) Plug in the device. Be careful here! Turn on the device and set the volume knob to 0. Set the multimeter to volts. One probe goes on the metal chassis (or somewhere where is it grounded, like on the ground pin of the STK) and the other probe on the output pins of each channel. The voltage should be very low, several millivolts. If you see numbers greater than 20 V (either negative or positive), the STK is shorted. Make sure you don’t accidentally short pins with your probe!
6) Lastly, check the voltage on the speaker terminals, with the device on, the multimeter set to volts and the speaker output turned on. Make sure you have contact on the probes, the black one goes to the black terminal and the red probe to the red terminal. If the relay is not clicking, you should have a very small voltage, because the device is in protection mode. If the relay has clicked or there is none and the STK is faulty, you should see a very high voltage, greater than 20 V usually.
7) If there are two STKs inside it is also a good idea to check the channel fuses, if there are any. If a fuse is blown on a channel, this usually indicates which STK is faulty.
Now, that you made sure you have a faulty STK, this is how you replace it:
1) Before installing the new STK, you should check the resistances on it like you did with the old one. This can save you a lot of effort if the new STK is also faulty.
2) Turn off the device. Unscrew the STK from the heat sink.
3) Desolder the pins from the PCB, using the solder wick and resin (or the desoldering gun). Tip: it is best to practice first on another PCB if you are new to soldering and desoldering, because STKs have pins really close to one another.
4) Take a square of toilet paper and wipe off the thermal paste from the heat sink. You can do the same with the old STK if you plan to keep it. The paste can’t be cleaned with water, so if you get it on your fingers it is best to wipe it off with TP.
5) Apply a small amount of thermal paste on the new STK and spread it in a thin, even layer on the metal back, covering it completely. Use a solid piece of plastic with a straight edge to do this. Old credit cards work well. I’m using a rectangle of transparent plastic I cut from a lid of a Muller Cremoso yogurt.
6) Place the new STK in the device. Make sure all the pins are in their holes. I find it useful to screw it slightly, so it stays in place when soldering.
7) Solder back the pins. Be careful not to short any.
8) Now take the multimeter and set it on connection check. Verify the connection between each pin and the next component it connects to on the PCB. You want to hear a beep everytime. Now check the connection between the pins of the STK, making sure they are not shorted. Some of them should beep, like the output pins on some models that are connected together. Refer to the electrical diagram for your STK.
And this should be it. Check again the new STK like you did with the old one, making sure nothing is shorted. Also listen for the relay clicking and check the speaker terminals. I recommend listening with a pair of cheap headphones and then with a pair of cheap speakers before connecting your actual expensive speakers, to make sure the new STK works well.
You can also replace a STK with a different model, but you have to make some adjustments to the circuit. You have to research further if this is the case.
A big problem is sourcing new quality STKs, because Sanyo doesn’t make them anymore. Aliexpress is a big hit or miss. I ordered one from there, waited almost two months for it and after installing it I discovered it was also faulty. There are also eBay sellers, but you should be wary of them, too. I find it best to order from a reputable online store that also has a physical address and offers warranty. If you are from Romania, I got three STKs from electronicservice.ro. They must also be Chinese, but look very well made and all of them worked. The store is also very professional.
If you want to read more on this subject, here are a few links with very useful information:
https://audiokarma.org/forums/index.php?threads/how-to-test-stk-ics.717075/
https://www.petervis.com/electronics/stk465/stk465.html (this entire site is very good)
That’s all I have. Don’t take my exact word for it, because I’m not very experienced and some of the info may be wrong. Maybe the more knowledgeable users can point out the wrong parts and offer their own advice.
