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Messages - DrGonz78

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With the TDA2030A chip running 36v power supply or rather a -/+18v supply it will be max rated at 20 watts as per data sheet. So now you will have the TDA2050 in place that can handle 32 watts at 8 ohms or the claimed 50 watts with 4 ohm load. In those examples though it is with a power supply capable of delivering 50v or -/+25v from the power transformer. Your amp will still have the -/+18v power supply and will have a new chip that is highly overrated to your amp's power supply. Honestly looking at the TDA2030 data sheet I think it's really only putting out 14 watts RMS with a 4 ohm load. I would be surprised if the 4 ohm speaker caused any trouble for TDA2050 chip.

I would just replace the chip as it is most probably bad.

You can measure those two bigger filter caps with your DVM to see if they are holding a charge. Chances are the caps discharge rather quickly and probably only millivolts will be stored. Still just put your meter across each one and check the voltage so you know. You don't have to discharge any of the other smaller caps.

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.


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 or 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.

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...

Amplifier Discussion / Re: Fishman Loudbox PRO-LBX-001 Schematic
« on: August 15, 2018, 03:54:40 PM »
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.

I 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.

Oh and turn off your cap lock. ;)

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

Schematics and Layouts / Re: Kustom Sienna 35 Pro schematic
« on: March 14, 2018, 02:26:51 PM »
I got this one here...

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