Tapco Thump TH-15A Amplifier repair

Thread Starter

HotBird

Joined Sep 10, 2020
10
Hi, guys!
By the way. I have the issue with Thump TH-15A - woofer doesn't work at all. HF speaker works.
What happend before. Power supply was broken and on the CON3 was +50V and -50V instead +28V and -28V. As a result blowed up C227 (47uF 63V). After fix power supply (replaced U102 TL431) on CON3 appeared normal +28V and -28V. HF cpeker start work but woofer doesn't. I replaced C227 and TDA8950TH - still no sound in woofer. I found that on woofer connector CON2 two pins are shorted between each other but not shorted to ground. Also on both pins is -28V. I don't know is it normal. When I switch on whole speaker I can hear click sound in woofer.
Can some one advice me how to fix woofer sound, please?
 

Thread Starter

HotBird

Joined Sep 10, 2020
10
What test equipment do you have access to?
I am repairing mobile phones more than 10 years and i have all equipment needed for soldering and diagnostic. But I don't have any special equipment for diagnostic audio amplifier. Also I don't have experience in repair audio amplifiers. Thats why I asking professionals for help.
 

JoeJester

Joined Apr 26, 2005
4,351
Thanks for the info. It helps us in determining a good course of action.

I'd recommend checking all the supply voltages to ensure they are correct. Then check CN10 for audio or on the amplifier chip.
 

JoeJester

Joined Apr 26, 2005
4,351
Yes, Dave is correct. Did you say the two output pins were shorted?

Review the datasheet to see how a single speaker is connected.

If your changing wires to inject a known signal, you should have not said you had all the diagnostic tools. The next person that I ask will have to tell me the make and model of all their test equipment they will be using.
 

Thread Starter

HotBird

Joined Sep 10, 2020
10
Swap input signals to compare if you don't have a scope.
I swaped today input signals (pins 2 and 4) and situation is the same - HF speaker works and LF speaker doesn't. It means that both input signals are working and problem is in LF amplifier. I checked both speakers: LF has 6 OHM, HF has 4 OHM.
 

Dodgydave

Joined Jun 22, 2012
9,410
Ok so LF amp is at fault, have you checked the chip supplies , disconnected the speaker and can you measure the output voltages.
 

Thread Starter

HotBird

Joined Sep 10, 2020
10
I did the measurement on the amp chip legs (TDA8950TH) with disconnected speaker and without input sound signal.

1 -25.3V
2 0V
3 28.8
4 0V
5 0V
6 5.5V
7 -21.2V
8 0V
9 0V
10 28.8V
11 0V
12 -25.7V
13 -25.2V
14 29.7V
15 -29.7V
16 -29.7V
17 -29.7V
18 -26.3V
19 -25.4V
20 -29.8V
21 -29.5V
22 -29.5V
23 29.7V
24 -25.4V
 
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