Acoustic 150 Low Volume

[guitman]

I have an Acoustic 150 guitar amp head. Been working fine until yesterday, when the output volume was very low.

All the inputs work, tone is fine and you can hear it, just nowhere near as loud as it should be.

I opened it up, there looks to be a burned spot on one of the boards. Could this be the cause? If so, do I just need to replace a burned transistor or does the entire board need to be replaced? Could it be that the massive blue capacitor is failing?

https://imgur.com/a/lVw5IJw

Service manual: http://bee.mif.pg.gda.pl/ciasteczkow...ice_Manual.pdf

Thanks!

[J M Fahey]

Sounds like you are helping somebody in another Forum.

Suggest he starts with the loop jack test , which is a sticky here.

I think we should create a sticky with basic initial tests which *everybody* should try first.

I am SICK of writing the exact same answers to the exact same questions hundreds of times.

[guitman]

Well, this is my first post on this website, I am not sure what you mean by "Sounds like you are helping somebody in another Forum."

There is no effects loop on this unit.

Yes, a sticky for basic troubleshooting would be nice.

[big_teee]

Hello new member.
You may wish to start here.
https://music-electronics-forum.com/...ad.php?t=42735
Please fill in more of your profile, since yours is completely blank.
Thanks,
T

[DrGonz78]

I opened it up, there looks to be a burned spot on one of the boards. Could this be the cause? If so, do I just need to replace a burned transistor or does the entire board need to be replaced? Could it be that the massive blue capacitor is failing?

Those burned looking areas are where there are wire wound resistors dropping voltage from higher voltage to lower voltages in the amp, they will dissipate heat and cook the board. Very normal for them to look like that and the board to still be okay. You need to confirm the power supplies for the high voltages in the amp and then the low voltages in the amp. The blue capacitor is the mains filter cap and it will remove AC ripple on the DC voltage power supply. Is the amp humming at 120hz?

If I had that amp opened up on my bench I would first hit some of those solder joints that look questionable. I see a few in your picture that jump right out at me immediately. I circled a few of them that look like they would benefit from some fresh solder re-flowed on the joints.

[guitman]

Very helpful DrGonz78, thanks! I will hit those solder joins and check high and low voltages.

Just to be clear, when checking high and low voltage, do I multi-meter test J with A and B contacts on the power board looking for around 60volts on each A/B? Here is a schematic from page 12 (PDF page 20) of the service manual.

=https://imgur.com/a/p15DUNq

I am not sure where to check the low voltages.

[tboy]

I think Juan is wondering what this is all about:

Posted byu/burninloins
17 minutes ago
Acoustic 150 Low Output Volume

Who is 'burninloins' and what was posted 17 minutes ago, and where?

[guitman]

Burnin Loins is my band. I also posted this on Reddit under my band's username earlier today which I used to copy and paste the info into this forum:

https://www.reddit.com/r/audiorepair...output_volume/

[AttachMan]

The preferred method of including reference material in a thread is to attach it to a post on this site, rather than linking to it elsewhere or embedding it from a non-local source.

[DrGonz78]

Just to be clear, when checking high and low voltage, do I multi-meter test J with A and B contacts on the power board looking for around 60volts on each A/B? Here is a schematic from page 12 (PDF page 20) of the service manual.

I am not sure where to check the low voltages.

Yes point J appears to be ground so black meter probe there and A & B (connects to R311) are tied together so red meter probe there. To check both high and low voltage meter at each side of R311. Which means red meter on each side of that R311 resistor each time have the black probe to ground to record the voltage.

[guitman]

The preferred method of including reference material in a thread is to attach it to a post on this site, rather than linking to it elsewhere or embedding it from a non-local source.

[ATTACH=CONFIG]52092[/ATTACH]

I feel like an idiot, but I do not see anywhere to attach items. All i see is add link, email, insert image, and insert video. Insert image simply asks me for a URL. I see no button to attach images to the thread. What am I missing?

[guitman]

Great, I will give this a shot this weekend and report back. Thanks!

[DrGonz78]

I feel like an idiot, but I do not see anywhere to attach items. All i see is add link, email, insert image, and insert video. Insert image simply asks me for a URL. I see no button to attach images to the thread. What am I missing?

As you post here the first few times it might not allow you to post files directly. As you get a few more posts those privileges are given to you. I am pretty sure this is why.

[Enzo]

When you post, look lower right of the post box. It says "Go Advanced". Click there, then the whole page opens up including attachment management features.

[nickb]

Burnin Loins is my band.

That's quite a relief. I was going to suggest a trip to Walgeen's might be in order.

Reminds me of a local band here: The Four King Dwarves (seriously, it's true).