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Author Topic: Need Help Repairing Pyle Guitar Amp after short circuit--only hums & pilot lite  (Read 5170 times)

Roark

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I would appreciate any advice repairing Solid State Pyle-pro PVAMP30 30-watt Guitar Amp after a short circuit--The amp only hums & the pilot lite comes on.

I needed to demo a Denon AVR-4800 home theater amp [250 watts per channel] for a buyer,but I had no speaker available.
In a hurry, I connected the Denon amp speaker outputs to the Pyle guitar speaker input clips,
but did not disconnect the spade end plugs that lead from the Pyle guitar amp section to the guitar speaker input clips.
And I accidentally powered on the Pyle guitar amp.

Increasing the volume at the Denon amp I finally heard a screech & maybe a pop.
Now the Pyle guitar amp only hums,& there’s no amplification--the pilot lite comes on [so the fuse is still good].

I opened up Pyle guitar amp section [I WAS careful to unplug the power cable first & not to touch the capacitors.]

I don’t see or smell any damage & I don’t see a 2nd fuse.

Haven't been able to find a schematic after  a bit of searching.

Should I send photos of the circuit board?
« Last Edit: August 21, 2018, 02:10:43 PM by Roark »

tonyharker

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You will have blown the power amplifier by connecting the external amplifier. It will be an IC or discrete transistor device.  A photo will show which.  If an IC it will probably easier to replace if you are competant to do that - can solder properly etc. A Transistor amp will be more complicated. If you are not sure it would be better to take it to a tech.

Roark

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Here's pic's. I guess it's a discrete transistor device. Is the power amplifier a set of components? & will they all need to be replaced or I must diagnose faulty components? Note: made in 2008. I have experience soldering.
How long might this take & how expensive?
« Last Edit: August 21, 2018, 03:35:40 PM by Roark »

DrGonz78

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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...
« Last Edit: August 21, 2018, 03:45:05 PM by DrGonz78 »
“A person who never made a mistake never tried anything new.” -Albert Einstein

Roark

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IC Chip   says: TDA2030A Do you need the rest?

D6 Diode: the top leg is burnt a bit!

Will measure DC voltage at the speaker connection [w speaker disconnected]: with amp powered on?
« Last Edit: August 21, 2018, 04:41:20 PM by Roark »

DrGonz78

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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...
« Last Edit: August 21, 2018, 04:43:30 PM by DrGonz78 »
“A person who never made a mistake never tried anything new.” -Albert Einstein

Roark

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IC Chip  says: TDA2030A . Thanks so much! This is exciting for me!

Roark

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https://www.wikihow.com/Measure-DC-Offset

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?
« Last Edit: August 21, 2018, 08:33:58 PM by Roark »

Roark

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What do think of a $1 TDA2030 IC Chip from China?

Enzo

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Probably fake.  A TDA2040 or 2050 would also work.  And an LM1875 would also drop in.

Roark

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Where would you suggest I buy the chip?

DrGonz78

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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
“A person who never made a mistake never tried anything new.” -Albert Einstein

DrGonz78

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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.
“A person who never made a mistake never tried anything new.” -Albert Einstein

Roark

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Using the DC Voltage meter, set to the 200mV range, I get a reading of exactly negative 1 when I touch the red probe to the red speaker lead [or a reading of  positive 1 when  reversing the probes].
This never fluctuates when slightly adjusting the contact with the probes, so I don't know if I  trust the reading .

I also smell a burnt/burning smell when I turn the amp on, on so I don't leave the amp on long. [I don't allow the amp to warm up for 10 min, as suggested in the guide.]
« Last Edit: August 22, 2018, 01:35:48 PM by Roark »

DrGonz78

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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.
« Last Edit: August 22, 2018, 02:54:33 PM by DrGonz78 »
“A person who never made a mistake never tried anything new.” -Albert Einstein