From an AR3 in a Paperboy machine discussed in a tech thread a while back.
Got the game working and then discover the left channel isn't working. PCB doesn't report errors on the various chips so we'll assume its the amplifier, speaker or wiring.
This has not been an easy fix for me and has probably taken about 8 hours total as I wasn't getting what I expected from it.
The sound was bleeding through when you turn the volume up high which suggested to me a few different things, i've documented the working out below for reference and anyone interested as always.
1) Switch right speaker cable over to left speaker - speaker works
2) Meter the pot - no problems
3) Test harness between board and pot - all fine
4) Test harness between AR3 and speakers - all fine
Most of the physical problems are taken care of here.
Time to find out whether its input or output
5) Use scope to look at waveforms going in and out - Pin 9 on AR3 (Audio 2+) used as reference as we know its working, sound going in, move to pin 1 (Audio 1+) waveforms going in there too.
6) Check pin 6 of AR3 (Speaker 2+) waveform out ok
7) Check pin 4 of AR3 (Speaker 1+) no waveform
Problem is on AR3.
I have TDA2030's on hand from a previous sound amp repair so I substitute the Q1 but no change, ok its time to make up a test loom.
I'm supplying power from an SMPSU using +12v, the TDA will run at lower than 18v and 22v which it normally gets is probably a bit warm but the operating specs say its fine. I've soldered on a test loop point so I can clip on the +12v and GND wires to fire up the audio section.
Time for a poke about, I scope a components and find I have an input signal at pin 1 of Q1 so the components leading to that seem ok right?
I can hear the speaker click when I power on so the amp is starting up.
I compare with Q2 and to me it initially looks the same.
After a lot of poking about and testing point to point and reflowing I figure that a couple of the caps aren't great so I replace them thinking the input signal has no return path to ground and can't make a circuit properly.
Still no change.
Then I realise on the scope that when I probe Q1 with the line centred on 0 my input signal floats around the zero line - i'm a sound engineer too so i'd assumed this was fine and then I scoped Q2's input and the line jumps up.
Hmmmm, the multimeter is telling me i've no bad tracks and i've got signal but what about voltage levels?
I meter the input at Q2 and its floating above 5v, check Q1's input and its 0.36v - ahhhh.
Looking a bit more closely at the schematics, the input signal is attenuated by the +22vDC line so unless i've got a blockage or a dead component dragging the line down then the voltage at input should definitely be higher.
I work through all the +22v input section towards pin 1 and everything is good.
Testing voltage at R12 at the +22 side, i've got +4.5 - as i'm only feeding +12 into this line this would make sense, however at the other end i've got next to zero.
After a few choice words with the board I lift up the pin 1 end of R12, right, i've now got ~4v.
Something on the input side is dragging it down.
I work around R3 and find still being 0v at pin 1.
Right, up comes a leg of C2 and there you are, i've got a nice ~5v unloaded at pin 1 and a bit of crackle on the speaker when I touch my meter probe to the pin.
Here's the C2
What I couldn't see was that on the schematics they look like caps that have no polarity, yet on the board a + sign is indicated so it was throwing me so I hadn't thought to check them with my ESR meter.
When I got out my loupe and could see the markings at 20x I could see these offending little items are marked 22u/50v - hmmmmm, i've just encountered early electrolytics in small packages.
I'd never seen them like this before.
Anyway, pop in a new 22uf/50v cap and the sound is now working on the left channel.
For good measure I decided to replace the cap on the right channel as well.
Not pictured above in the AR3 shot i've also changed out the C5 and C10 caps on the right channel.
I probably should have re-capped the outputs as well but don't have any 3300uf's on hand at 35v or better.
What i've learned from this experience:
TDA2030's are an easy amp to work with in principle, I could probably build a simple amp circuit now.
Inputs require attenuation - in audio we're used to dealing with very low voltages so you don't think about it in the amplifier stage.
You can be fooled by a 7p component!
Hope you enjoy my findings and experience here, next time your amp stops working on your AR2/3 it should be relatively easy to sort out.
I've got an AR2 thats got a buzzing channel so that'll be done next now I know what to look for, watch this space.
Got the game working and then discover the left channel isn't working. PCB doesn't report errors on the various chips so we'll assume its the amplifier, speaker or wiring.
This has not been an easy fix for me and has probably taken about 8 hours total as I wasn't getting what I expected from it.
The sound was bleeding through when you turn the volume up high which suggested to me a few different things, i've documented the working out below for reference and anyone interested as always.
1) Switch right speaker cable over to left speaker - speaker works
2) Meter the pot - no problems
3) Test harness between board and pot - all fine
4) Test harness between AR3 and speakers - all fine
Most of the physical problems are taken care of here.
Time to find out whether its input or output
5) Use scope to look at waveforms going in and out - Pin 9 on AR3 (Audio 2+) used as reference as we know its working, sound going in, move to pin 1 (Audio 1+) waveforms going in there too.
6) Check pin 6 of AR3 (Speaker 2+) waveform out ok
7) Check pin 4 of AR3 (Speaker 1+) no waveform
Problem is on AR3.
I have TDA2030's on hand from a previous sound amp repair so I substitute the Q1 but no change, ok its time to make up a test loom.
I'm supplying power from an SMPSU using +12v, the TDA will run at lower than 18v and 22v which it normally gets is probably a bit warm but the operating specs say its fine. I've soldered on a test loop point so I can clip on the +12v and GND wires to fire up the audio section.
Time for a poke about, I scope a components and find I have an input signal at pin 1 of Q1 so the components leading to that seem ok right?
I can hear the speaker click when I power on so the amp is starting up.
I compare with Q2 and to me it initially looks the same.
After a lot of poking about and testing point to point and reflowing I figure that a couple of the caps aren't great so I replace them thinking the input signal has no return path to ground and can't make a circuit properly.
Still no change.
Then I realise on the scope that when I probe Q1 with the line centred on 0 my input signal floats around the zero line - i'm a sound engineer too so i'd assumed this was fine and then I scoped Q2's input and the line jumps up.
Hmmmm, the multimeter is telling me i've no bad tracks and i've got signal but what about voltage levels?
I meter the input at Q2 and its floating above 5v, check Q1's input and its 0.36v - ahhhh.
Looking a bit more closely at the schematics, the input signal is attenuated by the +22vDC line so unless i've got a blockage or a dead component dragging the line down then the voltage at input should definitely be higher.
I work through all the +22v input section towards pin 1 and everything is good.
Testing voltage at R12 at the +22 side, i've got +4.5 - as i'm only feeding +12 into this line this would make sense, however at the other end i've got next to zero.
After a few choice words with the board I lift up the pin 1 end of R12, right, i've now got ~4v.
Something on the input side is dragging it down.
I work around R3 and find still being 0v at pin 1.
Right, up comes a leg of C2 and there you are, i've got a nice ~5v unloaded at pin 1 and a bit of crackle on the speaker when I touch my meter probe to the pin.
Here's the C2
What I couldn't see was that on the schematics they look like caps that have no polarity, yet on the board a + sign is indicated so it was throwing me so I hadn't thought to check them with my ESR meter.
When I got out my loupe and could see the markings at 20x I could see these offending little items are marked 22u/50v - hmmmmm, i've just encountered early electrolytics in small packages.
I'd never seen them like this before.
Anyway, pop in a new 22uf/50v cap and the sound is now working on the left channel.
For good measure I decided to replace the cap on the right channel as well.
Not pictured above in the AR3 shot i've also changed out the C5 and C10 caps on the right channel.
I probably should have re-capped the outputs as well but don't have any 3300uf's on hand at 35v or better.
What i've learned from this experience:
TDA2030's are an easy amp to work with in principle, I could probably build a simple amp circuit now.
Inputs require attenuation - in audio we're used to dealing with very low voltages so you don't think about it in the amplifier stage.
You can be fooled by a 7p component!
Hope you enjoy my findings and experience here, next time your amp stops working on your AR2/3 it should be relatively easy to sort out.
I've got an AR2 thats got a buzzing channel so that'll be done next now I know what to look for, watch this space.
