The other day I had my T1 Amp connected to my Beringer USB DAC which was connected (by USB) to a macbook. The macbook battery was getting low so I decided to connect it to the power supply while the AMP was on and playing music - big mistake! The music stopped and after 1-2 seconds I smelled the magic smoke coming out from the T1 amp (oh noes!!)
Looking at the Amp PCB I didn't see any clear signs of burnt stuff. I put my nose all over the place to track down the smell, it was coming from the STA510A, so I ended up ordering a new one. Today I replaced the STA510A with a new one, after powering up the Amp there are a few signs that something is wrong:
1) The R32 resistor heats up a lot instantaneously after power on. 2) The 5V rail (output of MC78M05) is not really 5V but a rather deceptive 4.49V. 3) The output relay turns on, even though the MUTE line is pulled up to 5V (mute is on, switch is disconnected).
EDIT: Measured a few more things: V+ is 35.4 V , then after the input diode (D1) it drops to 34.6 V (Vcc) which seems correct. Then after the big-ass R32 (Vin for 78M05), it measures 6V. Is this correct? 6V seems too low, it would explain why I'm only getting 4.5 V in the 5V rail. According to the 78M05 datasheet, the regulator has a 2V dropout which means the lowest recommended voltage for Vin is 7V.
If the regulator was sinking all the current, then R32 would have around 80mA of current flowing while dissipating around 3 Watts! This would explain why the resistor is heating up so much. But now, what would be sinking all the current in the 5V rail? I just replaced the STA510A chip, so I sure hope it's not the TC2000!
The PCB is v2.1 by the way.
almost 3 years ago
So today I did a few more measurements...
The +5V rail to SGND is 60 ohm which seems too low. Then the mute line (when pulled up to +5V) was measuring 0.5V! I checked the pullup resistor R6 and it was working fine, so the only way the signal was being pulled down was if the MUTE pin of the TC2001 was sourcing current. I desoldered the TC2001 chip, powered up the circuit and there you go: The 5V rail now measures 5V. The R32 resistor does not heat up anymore. The mute signal (betweem R6 and SW1) is now measuring around 5V.
Looks like my Tripath chip blew up as well :'( This chip is harder to source, does anymore know any stores where I can order from (preferably in Europe)?
almost 3 years ago
More updates to my monologue..
So the TC2001 chip just arrived from HongKong, replaced it on the PCB and tried out the T1 amp: - The 5V rail is now at 5V (this confirms the previous TC2001 chip was toast). - The R32 resistor does not heat up. - With the mute switch on, the relays are off, led light is off, no output. - After turning the mute switch off, the relays click after a second or so and the led turns on, unfortunately the speakers are silent. I must now investigate what's wrong, I suspect a dead cap in either the input or output stages. Ideas?