How do you check if an audio amp is receiving and/or sending audio?

[rewrite]

I'm not sure what tool is ideal for this, or what the general order of operations is in checking an audio circuit.

Assuming recapped and the volume pot checks out.

How do I check if audio is reaching the amp, and how do I check that it's coming out of the amp? Or is there something else to look for first?

 

[Derick2k]

An oscilloscope would be the best tool I think. But if its all analog audio we are talking about, one of them audio probes that have been made now and them should be good enough for like 80% of pcb audio circuits troubleshooting.

 

[rewrite]

An oscilloscope would be the best tool I think. But if its all analog audio we are talking about, one of them audio probes that have been made now and them should be good enough for like 80% of pcb audio circuits troubleshooting.

I've got one an oscilloscope. Don't know how to use it, but I have it, lol.

And I'm not sure what you mean about an audio probe but I'll search around.

 

[Derick2k]

An oscilloscope would be the best tool I think. But if its all analog audio we are talking about, one of them audio probes that have been made now and them should be good enough for like 80% of pcb audio circuits troubleshooting.

I've got one an oscilloscope. Don't know how to use it, but I have it, lol.
And I'm not sure what you mean about an audio probe but I'll search around.

You already have the best tool then, start playing with it, reading up and watching youtube videos on how to use them. I was going to do a simple basic use post on them, but I just dont have the time for it, plus Im really bad as a teacher lol.

https://www.arcade-projects.com/for...-walsdawg-arcade-audio-probes.6183/post-93080
Mitsu was selling some but no longer, we were trying to get another run going but didnt happen. There are some designs floating around/some still sell some on other sites I think.

 

[rewrite]

There are some designs floating around/some still sell some on other sites I think.

Looks like B&K makes something similar for $40. Will pick one up.

You already have the best tool then, start playing with it, reading up and watching youtube videos on how to use them.

I know you can see how signals look with it, but I wasn't sure if just a probe or something would give a quicker/easier answer. Which seems to be the case.

I've been making big strides learning and fixing some PCB's lately, and wanted to tackle a couple no sound ones I've had laying about since that seems fairly simplistic

 

[brizzo]

You can make an audio probe using a basic piezo speaker. Connect black wire to ground, then attach something pointy to the positive wire and poke around the circuit with it. Easy to find where audio signal begins and ends (pre and post amplification)

 

[caius]

Some time ago I designed an audio probe made of few components, it works very well.

 

[benime]

https://www.amazon.com/Elenco-Electronics-LP-560-Logic-Probe/dp/B000Z9HAP4

It's got a speaker on it; a shitty speaker, but it's enough to tell if you have analog audio.

 

[rewrite]

https://www.amazon.com/Elenco-Electronics-LP-560-Logic-Probe/dp/B000Z9HAP4

It's got a speaker on it; a shitty speaker, but it's enough to tell if you have analog audio.

I actually have one of these... I didn't know I could use it for this.

 

[kuze]

https://www.amazon.com/Elenco-Electronics-LP-560-Logic-Probe/dp/B000Z9HAP4

It's got a speaker on it; a shitty speaker, but it's enough to tell if you have analog audio.

Interesting, did not know you could use those for this purpose!

 

[benime]

https://www.amazon.com/Elenco-Electronics-LP-560-Logic-Probe/dp/B000Z9HAP4

It's got a speaker on it; a shitty speaker, but it's enough to tell if you have analog audio.

I actually have one of these... I didn't know I could use it for this.

https://www.amazon.com/Elenco-Electronics-LP-560-Logic-Probe/dp/B000Z9HAP4

It's got a speaker on it; a shitty speaker, but it's enough to tell if you have analog audio.

Interesting, did not know you could use those for this purpose!

Yeah, it's super handy. I don't think the 900 has a speaker, but the 560 definitely does and it's enough for troubleshooting. Low freq stuff doesn't come through too well on it, so be mindful of the board you're working on. I had a WWF Wrestlefest I was troubleshooting and the attract music was a little tough to make out, but something like the Bubble Bobble theme (troubleshooting an issue with a bootleg I picked up recently) comes through just fine, albeit crackly and overdriven, but it's recognizable.

 

[rewrite]

I'm going to sound real dumb here, but @benime, is it as simple as power the probe, then touch it to say the input or output pin on the amp?

 

[benime]

I'm going to sound real dumb here, but @benime, is it as simple as power the probe, then touch it to say the input or output pin on the amp?

Not dumb, and yeah. If you're troubleshooting something JAMMA, the easiest thing to do is use some male-to-male Dupont test leads and poke them into the slot connector at Ground and +5V, otherwise you'll need to find somewhere you can clip on to pull Ground and +5V directly on the board. Also, it has to be either directly on the board or from the same power supply as the unit under test in order for the probe to work.

To make sure it's powered, just touch your finger to it and you'll hear a buzz, probably register both low/high.

 

[rewrite]

@benime oh cool.

Yeah, I knew how to power the probe to use it and check for activity on different chips and cpus, but I didn't know if it was any different to check the audio.

Sometimes an assumption in this hobby turns into things getting fried, so it's usually better to ask!

I have the exact one you linked and it says "Your last purchase on...", so I'll give it a shot today on a known working game!

 

[RandomRetro]

Always like it when you see an active thread on the topic you are dealing with...

I have a Namco board with no audio and going to pick up one of these probes to try it out with my testing. Thanks for asking the questions @rewrite and thanks for the suggestions @benime

 

[rewrite]

I could not get this to work. It just reads the input/output as high or low and beeps loudly constantly.

 

[benime]

I could not get this to work. It just reads the input/output as high or low and beeps loudly constantly.

And it's a known working board? Depending on the chip, make sure it's set to either TTL or CMOS, and Pulse.

Here's what I get just testing with DDP DOJ.

https://photos.app.goo.gl/bb7sQUq3eenhQLbSA

 

[rewrite]

Oh, hmm. I was checking off of the amp's (MB3737A) input and output pins. Maybe that was my mistake.

And it's a known working board? Depending on the chip, make sure it's set to either TTL or CMOS, and Pulse.

Sure is.

I used Liquid Kids for trying this out, and it was still playing music just fine off of the supergun while doing so.

 

[benime]

Oh, hmm. I was checking off of the amp's (MB3737A) input and output pins. Maybe that was my mistake.

And it's a known working board? Depending on the chip, make sure it's set to either TTL or CMOS, and Pulse.

Sure is.
I used Liquid Kids for trying this out, and it was still playing music just fine off of the supergun while doing so.

Directly off the amp should work the same, so long as the volume is turned up. I just tried it and I do hear the constant 'high' beep, but I can also hear the audio over the speaker, but I had to turn up the volume.

 

[RandomRetro]

Here's what I get just testing with DDP DOJ.

Those are some hot jams! @benime. Not to derail the thread, but seeing it in the video made me remember that I need to put a new fan on my DDP DOJ Case. Do you know the replacement specs by chance?

On the topic of the thread, I needed a logic probe so this thread also got me to pull the trigger. Thanks for the example video.