Hey everyone, new here. Ive got a couple amps I am using to teach myself how to repair them. One is an A/D/S power plate 80 and the other is a 120. They both use these STK (80 is STK082g and the 120 is STK086g) output ICs. I have made some progress with them, but I want to just focus on the 80 right now. The 120 seems to be of similar construction, so hopefully learning one will lead to knowledge to fix the other. I have read up a bit on bcae1s website to get a better understanding, but since we have output ICs here, Im a little in the dark.
So, here is the story on the 80 and what I have found and done. Initial power up, no current draw to speak of. Replace two transistors (one had a hole in it) with the part number B829. Attempt to power up again. Massive hard 20A current spike. So, shut power off, desolder both ICs and current is fine when powering up the power supply board. Resolder ICs one at a time and find teh defective one. Removed that and left the (what I presume to be good) one in. Power it back up. massive draw gone, but what I assume is protection mode is present. Audio is cutting in and out of that channel every second or so. So I desolder what I *think* are the rail voltage wires coming off of the bridge rectifier and the protection mode seems to be gone. No more blip on the current meter on the power supply. So, I wait for the replacement STK to arrive and install it. Now both channels are doing the same thing, so we have some progress. Measure voltage across the output from the bridge rectifier and I am getting about +/-33Vdc. Seems normal?
Just for fun, I desoldered the original IC just to be sure it wasnt the culprit and I still have the same issue. Any idea what I should check next? Thanks for any help!
So, here is the story on the 80 and what I have found and done. Initial power up, no current draw to speak of. Replace two transistors (one had a hole in it) with the part number B829. Attempt to power up again. Massive hard 20A current spike. So, shut power off, desolder both ICs and current is fine when powering up the power supply board. Resolder ICs one at a time and find teh defective one. Removed that and left the (what I presume to be good) one in. Power it back up. massive draw gone, but what I assume is protection mode is present. Audio is cutting in and out of that channel every second or so. So I desolder what I *think* are the rail voltage wires coming off of the bridge rectifier and the protection mode seems to be gone. No more blip on the current meter on the power supply. So, I wait for the replacement STK to arrive and install it. Now both channels are doing the same thing, so we have some progress. Measure voltage across the output from the bridge rectifier and I am getting about +/-33Vdc. Seems normal?
Just for fun, I desoldered the original IC just to be sure it wasnt the culprit and I still have the same issue. Any idea what I should check next? Thanks for any help!
Only one amp per thread so if you decide to post for the 120, do so in a different thread.
Post photos of the internals of the amp.
The 8829 is likely a date code, not the part number.
Most of the STK modules are counterfeit. They sometimes work but reliability varies, to some degree, on how the amp is used.
Look up the datasheet for the modules and measure the resistance from the output terminals to the rail supply terminals. Do any read near 0 ohms?
Post photos of the internals of the amp.
The 8829 is likely a date code, not the part number.
Most of the STK modules are counterfeit. They sometimes work but reliability varies, to some degree, on how the amp is used.
Look up the datasheet for the modules and measure the resistance from the output terminals to the rail supply terminals. Do any read near 0 ohms?
Thanks for the feedback. Here is a pic of the 80. My focus is on the 80 and I hope it will teach me to fix the 120 based on the identical symptoms. Yes, I know that identical symptoms do not mean identical causation. But Im learning here.
to be clear, B829 is the transistor, not 8829. Here is a link of what I found on teh datasheet. Also, be aware there was literally a hole in one of them.
B829 Datasheet PDF - SANYO -> Panasonic
I have learned that these ICs can be counterfeit. Obviously, after I bought them haha. Any true way to verify this? I dont mind finding out they are counterfeit after running it hard or even mediocre. I just want to get this thing running at idle.
I will check out your suggestion of checking the output terminal resistance VS the rail voltage terminals.
Thanks again for your help! Its much appreciated! Sorry if my presentation is poor or I am not offering pertinent information that others normally would. This is very new to me. I have the tools, some basic knowledge, but almost no experience in this. So, I appreciate you bearing with me.
to be clear, B829 is the transistor, not 8829. Here is a link of what I found on teh datasheet. Also, be aware there was literally a hole in one of them.
B829 Datasheet PDF - SANYO -> Panasonic
I have learned that these ICs can be counterfeit. Obviously, after I bought them haha. Any true way to verify this? I dont mind finding out they are counterfeit after running it hard or even mediocre. I just want to get this thing running at idle.
I will check out your suggestion of checking the output terminal resistance VS the rail voltage terminals.
Thanks again for your help! Its much appreciated! Sorry if my presentation is poor or I am not offering pertinent information that others normally would. This is very new to me. I have the tools, some basic knowledge, but almost no experience in this. So, I appreciate you bearing with me.
OK. So it's a 2SB829. Where did you find them? If ebay or amazon, expect counterfeits.
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You asked about determining if the modules are original... I don't know if it's possible without opening the module, likely making it unusable. There are photos of counterfeit modules (opened) online.
Ok, well im not going to cut them open just yet. I did measure what I think to be the output and rail voltage input resistance at pins 7 and 11 on three ICs. One known bad, one suspected good, and one Unk. All have about 21MOhm between pins 11 and 7. Now, I am new to this, but I suspect I have the right pins. Here is a link to the data sheet. Also, here is a schematic I found on this website that seems very similar to this circuit design.
STK082G datasheet
https://www.diyaudio.com/forums/att...98069-ads-power-plate-120-repair-adsps501-png
thanks again!
STK082G datasheet
https://www.diyaudio.com/forums/att...98069-ads-power-plate-120-repair-adsps501-png
thanks again!
If the output stage failed (causing excessive current draw), I'd expect a low resistance from 7 to 6 or 8?
That would be definitive. It's possible for them to fail in other ways.
That would be definitive. It's possible for them to fail in other ways.
6/7 is 3 Ohms on the known bad one. known good one is open.
But still, these are both removed from the amp. Amp still acts the same with known good one (well, at least suspected known good) installed.
So, symptoms are as follows:
1. rail voltage supply proper on both sides
2. audio output does function
3. audio output cuts out every second or so
4. disconnect rail voltage supply and ammeter tick (only maybe an amp, not a good meter on the power supply) goes away.
So there is something amiss on the audio board, but im not sure exactly what to look at.
But still, these are both removed from the amp. Amp still acts the same with known good one (well, at least suspected known good) installed.
So, symptoms are as follows:
1. rail voltage supply proper on both sides
2. audio output does function
3. audio output cuts out every second or so
4. disconnect rail voltage supply and ammeter tick (only maybe an amp, not a good meter on the power supply) goes away.
So there is something amiss on the audio board, but im not sure exactly what to look at.
Connect a load to the channel without the module to see if that makes a difference in the amp shutting down/cutting out.
When the amp shuts down, does the power supply shut down or does the amp simply go into muting?
When the amp shuts down, does the power supply shut down or does the amp simply go into muting?
So, connect speaker to speaker connections, power up amp, make sure neither output ICs are installed and see what I get? Ive powered it up with both ICs removed and rail voltage lines connected from power supply board to audio board and one second tick still happens. Would connecting a speaker to the output side have any change in effect here?
When the amp is ticking (I suspect this is protection mode?), the amp just mutes. I have not put a meter on the rail voltage when its doing this though. I can certainly do that if needed!
When the amp is ticking (I suspect this is protection mode?), the amp just mutes. I have not put a meter on the rail voltage when its doing this though. I can certainly do that if needed!
Do you have a scope?
I don't have the exact diagram for this amp so I don't know what sort of protection it has (we don't even know if it's actually going into protection). Having a load connected to the output terminals may stop it from going into DC offset protection.
I don't have the exact diagram for this amp so I don't know what sort of protection it has (we don't even know if it's actually going into protection). Having a load connected to the output terminals may stop it from going into DC offset protection.
I do have a couple scopes. Ive just been using a Fluke 97 scopemeter for now. I have a Lectrotech single channel scops, but no scale as its missing.
I only have one speaker that I have been using on each channel when testing, but I cant see if everything was fine not having the other channel not connected creating this symptom.
any thoughts on what I might check with the scope?
I only have one speaker that I have been using on each channel when testing, but I cant see if everything was fine not having the other channel not connected creating this symptom.
any thoughts on what I might check with the scope?
If the modules are out, just jump the terminals of each channel with a wire.
A scope will tell you far more than a multimeter. For example, you could immediately tell if the supply was shutting down by looking at the waveform on the primary or secondary windings. Looking at the rail voltage may be misleading because the rail caps could remain charged after the supply shuts down.
Please (and this applies to anyone who needs repair help) use your sig line to list all equipment you have, editing it as equipment changes. Include the model numbers.
Top of page, menu USER CP >> EDIT SIGNATURE
Oscilloscope (yes or no)
Multimeter(s)
Type of signal source (grounded RCA shields preferred).
Soldering iron
Desoldering pump
Power supply
2 ohm current limiting resistor (hollow cylindrical ceramic 100w preferred)
A scope will tell you far more than a multimeter. For example, you could immediately tell if the supply was shutting down by looking at the waveform on the primary or secondary windings. Looking at the rail voltage may be misleading because the rail caps could remain charged after the supply shuts down.
Please (and this applies to anyone who needs repair help) use your sig line to list all equipment you have, editing it as equipment changes. Include the model numbers.
Top of page, menu USER CP >> EDIT SIGNATURE
Oscilloscope (yes or no)
Multimeter(s)
Type of signal source (grounded RCA shields preferred).
Soldering iron
Desoldering pump
Power supply
2 ohm current limiting resistor (hollow cylindrical ceramic 100w preferred)
Thanks, will edit. Sorry, Im all new to this. Also, I do appreciate your time and I have been reading your website as well. Seems this IC setup is a bit unique for older amps.
I will try that with ICs out and rails still connected and report back.
also will update with what I have for test equipment. Probably going to get a current limiter of some type so I dont melt anything. That 24a spike after I replaced the transistors threw me for a scare.
I will try that with ICs out and rails still connected and report back.
also will update with what I have for test equipment. Probably going to get a current limiter of some type so I dont melt anything. That 24a spike after I replaced the transistors threw me for a scare.
Ok, both ICs removed and now for some reason I only have 33V neg on one side. The pos side is at about 1v. Possibly an issue with the cap on the pos side? Or maybe an issue with the rectifier?
It's not likely to be a shorted cap. That would cause excessive current draw.
It could be a bad solder joint, open trace, or a defective rectifier (if there is input to the rectifier but nothing on it's output terminal).
Side note, you rarely need a precisely accurate amp meter on your 12v power supply. For the most part, you only need to be able to see movement and be able to see if the change in current is minor or excessive.
It could be a bad solder joint, open trace, or a defective rectifier (if there is input to the rectifier but nothing on it's output terminal).
Side note, you rarely need a precisely accurate amp meter on your 12v power supply. For the most part, you only need to be able to see movement and be able to see if the change in current is minor or excessive.
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Ok more testing shows that input to rectifier with rectifier remove is 33vac. still only getting on leg of rail voltage at this point. Swapped in another rectifier just to see, and same result.