I'm on to my next project after fixing an Onkyo receiver that had a bad display - https://www.diyaudio.com/community/threads/onkyo-tx900-display-not-working.405419/
I picked up this ADS Power Plate amp a few months ago and finally had time to put it on the bench and test it.
It powers up, the power light turns green, but doesn't have any output on any speaker output.
So I opened it up and the most obvious thing I see is this destroyed resistor.
I'm still working my way through Perry's tutorial, I have been reading a few pages every night trying to work my way through it finally.
But for now I am assuming that the burned resistor is the same spec as the good one to the right, so I ordered a few 1W 100 Ohm resistors. I will pull the board this weekend and start removing the resistor and also testing the other components nearby.
I'm thinking that the transistor near it has shorted causing too much current through the resistor. So I'm assuming I will need to replace that transistor. There is also a Zener Diode behind the resistor that I need to test and possibly replace. And I ordered some capacitors to replace the two that might have been damaged when the resistor burned.
I'm also guessing it makes sense to replace the components near it that look to be for the other channel? Since I'm in there.
I don't have a schematic for this amp and haven't found one online. There are a few ADS photos in Perry's tutorial but none that match it exactly.
If anyone has any other tips while I keep working through the tutorial and wait for parts I'm all ears! I'm still learning, happy for the help!
Thanks,
Ian
I picked up this ADS Power Plate amp a few months ago and finally had time to put it on the bench and test it.
It powers up, the power light turns green, but doesn't have any output on any speaker output.
So I opened it up and the most obvious thing I see is this destroyed resistor.
I'm still working my way through Perry's tutorial, I have been reading a few pages every night trying to work my way through it finally.
But for now I am assuming that the burned resistor is the same spec as the good one to the right, so I ordered a few 1W 100 Ohm resistors. I will pull the board this weekend and start removing the resistor and also testing the other components nearby.
I'm thinking that the transistor near it has shorted causing too much current through the resistor. So I'm assuming I will need to replace that transistor. There is also a Zener Diode behind the resistor that I need to test and possibly replace. And I ordered some capacitors to replace the two that might have been damaged when the resistor burned.
I'm also guessing it makes sense to replace the components near it that look to be for the other channel? Since I'm in there.
I don't have a schematic for this amp and haven't found one online. There are a few ADS photos in Perry's tutorial but none that match it exactly.
If anyone has any other tips while I keep working through the tutorial and wait for parts I'm all ears! I'm still learning, happy for the help!
Thanks,
Ian
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Those resistors are not physically the same size are they?
All of that brown fixative has likely become both conductive and corrosive and needs to be removed.
All of that brown fixative has likely become both conductive and corrosive and needs to be removed.
They certainly aren't the same size now! But after looking at the groupings there it looks like the two groupings are the same (semiconductor, two caps, small resistor, larger resistor and zener diode). But it might be easier to tell from the bottom traces.
Maybe? I'm still trying to figure out the layout. I understand how non-car people feel when I pop the hood on a car and start pointing to stuff!
I was reading through the Amplifier basics section again last night and came across the section on DC pulses. So this morning I went to check and sure enough there is a big ~10V pulse on the speaker terminal when you turn on the amp, then a bigger ~ -15V pulse, then it settles down to about 0.02V.
It sounds like the protection circuit is kicking in. But the LED stays green. And I'm assuming it's not working properly since that resistor is blown, and probably the semiconductor near it. Once I get it off the board I can figure out what it is.
Thanks again for the tips!
I was reading through the Amplifier basics section again last night and came across the section on DC pulses. So this morning I went to check and sure enough there is a big ~10V pulse on the speaker terminal when you turn on the amp, then a bigger ~ -15V pulse, then it settles down to about 0.02V.
It sounds like the protection circuit is kicking in. But the LED stays green. And I'm assuming it's not working properly since that resistor is blown, and probably the semiconductor near it. Once I get it off the board I can figure out what it is.
Thanks again for the tips!
Do you read 0 ohms between one end of the resistor and either power supply terminal of the op-amps?
You look like you have a current boost transistor shunt regulator. The PQ10 has only a basic shunt regulator for its single op-amp.
Are 443 and R444 serving the same purpose (feeding the Zener)?
Did you check the resistance across that fixative?
You look like you have a current boost transistor shunt regulator. The PQ10 has only a basic shunt regulator for its single op-amp.
Are 443 and R444 serving the same purpose (feeding the Zener)?
Did you check the resistance across that fixative?
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Use your meter to see if there is a 0 ohm connection.
Yes.
Get rid of all of that fixative. TT7, item #14.
Yes.
Get rid of all of that fixative. TT7, item #14.
OK between either leg of resistor R443 (the burned one) or R441 (the good 100 ohm resistor) and B+ on Op-Amp 5 I get 0.39 M ohm.
And between either leg of R443 and R441 and B- of Op-Amp 5 I read 1.4 M ohm
I removed as much fixative as I can for now, at least enough to hopefully break any connection.
And between either leg of R443 and R441 and B- of Op-Amp 5 I read 1.4 M ohm
I removed as much fixative as I can for now, at least enough to hopefully break any connection.
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OK. The two transistors there are used to boost the current. Audio troubleshooting page, item #23. Check from the emitters of the transistors to the supply terminals of the op-amps.
Sounds good, I'll check that tonight. I'm also going to set up your new tutorial on an old computer that I can leave down in the shop so I can stop running up and down the stairs every time I need to check something!
From the emitter on Q415 to B+ on the op-amp I read 32.2 ohms
to B- on the op amp I read 2.2 M ohms
From the emitter on Q419 to B+ on the op-amp I read 1.6 M ohm
to B- on the op amp i got 0.1 ohm, which is probably the resistance of my leads
i will keep reading and see if i can figure out that that means.
to B- on the op amp I read 2.2 M ohms
From the emitter on Q419 to B+ on the op-amp I read 1.6 M ohm
to B- on the op amp i got 0.1 ohm, which is probably the resistance of my leads
i will keep reading and see if i can figure out that that means.
For now I'm just bringing down a laptop that I will set out of the way unless I need it. If I can find a cheap monitor I will set up an old desktop down there.
If you don't have an old desktop, ask around. There are plenty taking up space in closets and attics that people would love to get rid of.
You can buy really decent older refurbed Dells and HPs on ebay. The tutorial is not, in any way demanding. In my shop, I used an old dual core Dell with an SSD and couldn't tell it wasn't a modern computer except for booting up. For the monitor, the VESA mount is key.
When you pull the board, you can follow the traces to see why there is resistance in the B+ supply. There is a discrete regulator troubleshooting section. ATS link in Quick Links, then iten #24.
You can buy really decent older refurbed Dells and HPs on ebay. The tutorial is not, in any way demanding. In my shop, I used an old dual core Dell with an SSD and couldn't tell it wasn't a modern computer except for booting up. For the monitor, the VESA mount is key.
When you pull the board, you can follow the traces to see why there is resistance in the B+ supply. There is a discrete regulator troubleshooting section. ATS link in Quick Links, then iten #24.
I'm a bit of a pack rat so I have two desktops kicking around that I really should recycle. I was going to pull the power supply out of one to run a 12V stereo in my garage, then donate the rest. I'm short on monitors, but Goodwill always has them for $20 and I bet a neighbor has one they want to give away.
I also brought home a few older laptops when I was helping my parents clean out their house, so I have plenty of old PCs kicking around. Unfortunately most browsers no longer support Windows 7, so the one I have that someone wiped and recreated needs browser updates. I think I have it working now, I just need to get flash to work on it.
I'm also fighting a cold so I'm not 100%.
So it sounds like it's time to pull up the board! Yay, that doesn't look like fun.
I also brought home a few older laptops when I was helping my parents clean out their house, so I have plenty of old PCs kicking around. Unfortunately most browsers no longer support Windows 7, so the one I have that someone wiped and recreated needs browser updates. I think I have it working now, I just need to get flash to work on it.
I'm also fighting a cold so I'm not 100%.
So it sounds like it's time to pull up the board! Yay, that doesn't look like fun.
I don't know which browsers won't work on Win7. I've never gone to win10 and with the exception of Microsoft's latest win10 browsers, I can run most everything. Win7 is all you need.
This amp looks simple. You should try some of the Alpines.
This amp looks simple. You should try some of the Alpines.
Sunday I decided to clean off my workbench since I still wasn't feeling well. Good decision. Last night's work was much more enjoyable having more space.
Last night I pulled off both resistors and removed one end of both zener diodes. One of them was bad, it reads 0 volts in both directions. The other tested correctly, 0.7V in one direction, nothing in the other.
I also removed one of the transistors and was able to read that it's a TIP 41C, so I will order a few of those. I ran out of time before I was able to test the transistor. It was also a major pain to remove, I need to improve that skill.
I'm still feeling like a parts swapper, but the various pieces of the amp are starting to come into focus. I will keep reading while I wait for the transistors and any other parts I need to come in. Then hopefully I can swap them back in and test it again.
Last night I pulled off both resistors and removed one end of both zener diodes. One of them was bad, it reads 0 volts in both directions. The other tested correctly, 0.7V in one direction, nothing in the other.
I also removed one of the transistors and was able to read that it's a TIP 41C, so I will order a few of those. I ran out of time before I was able to test the transistor. It was also a major pain to remove, I need to improve that skill.
I'm still feeling like a parts swapper, but the various pieces of the amp are starting to come into focus. I will keep reading while I wait for the transistors and any other parts I need to come in. Then hopefully I can swap them back in and test it again.
One regulator is NPN and the other is PNP, very likely. TIP42 would be the other one. MTX is one of the few amps that don't use complementary transistors. The datasheet will often show complementary transistors. Sometimes, the datasheet for one shows both (TIP35 and 2n6488, for example). The TIP is in the 'semiconductor datasheets' folder.
Thanks, super helpful tip which having just read the regulator section I should have picked up on. I will see if I can read the other one, but plan on ordering both.