Well if set to max range of 200mv the meter would not be able to read +/- 1. What you are measuring is simply an out of range symbol for the meter. Do you have 200mv, 2v, 20v, 200v, 700v as the range selections? Try putting the meter on 200v setting and then what does it say?

Edit: Also the burning smell is probably that diode leg cooking so yes don't keep the amp on very long at all. Just take measurement to confirm DC on the output.

Quote from: Roark on August 21, 2018, 05:21:23 PM

I will measure DC voltage at the speaker connection using a VOM [is this similar to DC-Offset measurement in link above as described above?],& with amp on ---correct?

I no longer know the polarity of the red & blue speaker wires coming from the amp to the speaker. 
Can I damage the VOM by connecting the positive probe of the VOM to the negative speaker wire, or vice versa?

You probably already figured this out but Yes with the amp on.

Also if you don't remember the polarity of the speaker wires you can use your DVM to figure it out. When doing resistance checks always turn off the amp and even unplug it for added safety. Measure blue wire with Red probe and place the black probe to the chassis, and do the same with the blue wire. Blue is probably negative and red is probably positive. The negative terminal will be grounded to the chassis and will read near 0 ohms resistance. The Positive will terminal will have a bit of resistance relative to ground. This method should work for this amp.

When you measure to check for DC voltage at the speaker leads it will not damage your DVM having Red probe on negative or vice versa. Black lead to negative and Red lead to positive terminal. As example you might see 20V that way and when you reverse the meter leads it will then display -20V. So it just changes the reference point of ground.

Typically we say don't buy it on eBay since there are so many fakes there... However, I have personally bought from this seller before and feel okay recommending him to others. You can search mouser.com or digikey.com for the LM1875 IC chip but you won't find brand new manufactured TDA2030, TDA2040 or TDA2050. So that is why we go to eBay to find them and buyer beware of fakes. I still feel safe buying this particular chip from the seller I listed though.

https://www.ebay.com/itm/1-x-TDA2050-32W-Hi-Fi-Amplifier-IC-USA-SELLER-FAST-FREE-USA-SHIPPING/301246868204?hash=item4623b66aec:g:uV4AAOxy69JTGjHO

Yeah look at the picture here and I circled the output IC chip. It is bolted down to what we refer to as a heat sink, which helps the component expel heat through the metal. Look on that chip that is bolted down and try to read what it says. The diode is in question too if it is burnt as well as the trace of copper on the board that it connects to.

Edit and ADD... The IC power opamp should look identical or similar to this...

The hum you hear is DC voltage on the speaker and that is bad for the speaker, so disconnect the speaker when powering up the amp. At this point I would guess the IC chip is probably a TDA2030 or something similar. The other thread you started on the MEF website had G1 asking you to measure DC voltage at the speaker connection. Do this but remove the speaker first since it probably has DC volts and it's not worth leaving connected at this point. So start by identifying the IC chip in there connected to that heat sink. Look at the top body of the component for a part ID.

P.S. Not sure but that D6 Diode looks like the top leg got smoked a bit?? Please confirm...

Not sure if they will support you on this specific product?? But I did call Fishman when I was fixing loudbox mini and they were very receptive to my call. In fact, they offered repair rate that seemed reasonable and they helped me out with schematics. Now that might be the result that the model I was trying to fix was far past being a warranty repair. Not sure about your product but it is worth the time to call... They have general 1-800 type number and international type too.

https://www.fishman.com/contact/

Check this out...
https://supportloudtech.netx.net/loud-public/#category/13332

Quote from: s3gle on May 05, 2018, 05:02:52 AMI believe all speakers are running at 8 ohms. my guess is that the splice will create 16 ohms per output, which should be ok?

It depends on how you will wire the splice, parallel or series. Typically wiring two 8 ohm loads in series becomes 16 ohms and wiring two 8 ohm loads in parallel will become 4 ohms. On the stage amp how are the speakers wired, parallel or series? Also, what is the impedance of each speaker separately on both amps? Do you have ohms meter to check DC resistance of the connections that you intend on creating? I wouldn't power anything up until you really suss this one out. 

The two black .022uf caps on the right side are coupling caps non-polarized and the stripe indicates foil side. The single black .03uf is coupling cap non-polarized stripe indicating foil side. The last two caps are polarized electrolytic caps, not sure value, but they might be cathode bypass capacitors. On those electrolytic caps what does each end connect to?

Wow a great schematic indeed. Do you have a voltmeter handy? You need to check all your power supply voltages and make sure that all checks out good. After that you need to consider how you can go about signal tracing the amplifier. Scopes are the preferred manner by which amp techs use to trace a signal through a circuit. If you do not have a scope then you need to google the term "Signal Tracer" and build a DIY version. These two steps will get you going in the right direction.

P.S. You only need one thread here about the amp you are fixing. If anything posting many threads about the same amp is just confusing "US", the people trying to help.

Post the schematic or we will have little to no way of helping. Also, it will get a bit confusing having more than one thread asking questions about the same thing.

Quote from: phatt on April 10, 2018, 09:39:10 AMOh and turn off your cap lock.
Phil.

I was thinking the volume was weak so he was making sure we could hear him.  :lmao:

I got this one here...

Sorry I had to post something to just laugh at this thread... Good thing Juan didn't chime in yet...  :dbtu:

I remember this thread... If you look back through it there are schematics given by Galaxlex.

https://www.ssguitar.com/index.php?action=dlattach;topic=3850.0;attach=7551

https://www.ssguitar.com/index.php?action=dlattach;topic=3850.0;attach=7553

https://www.ssguitar.com/index.php?action=dlattach;topic=3850.0;attach=6703