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Rabbit 16v 20th November 2020 01:27 AM

A/D/S power plate 80 and 100
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!

Perry Babin 20th November 2020 03:15 AM

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?

Rabbit 16v 20th November 2020 05:42 AM

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.

Perry Babin 20th November 2020 05:50 AM

OK. So it's a 2SB829. Where did you find them? If ebay or amazon, expect counterfeits.

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Rabbit 16v 20th November 2020 06:14 AM

1 Attachment(s)
I got the transistors on Mouser. So hopefully they are ok. The one did go from hole in it to not a hole in it, so I think thats a bonus.

sorry I forgot the attachment. Vbulletin is really a timewarp, haha. Hopefully its there now.

Thanks again!

Perry Babin 20th November 2020 06:30 AM

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.

Rabbit 16v 21st November 2020 10:16 PM

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

thanks again!

Perry Babin 21st November 2020 10:39 PM

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.

Rabbit 16v 21st November 2020 11:00 PM

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.

Perry Babin 21st November 2020 11:10 PM

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?

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