Sjöström Audio DIY forum

2 mV typ and max 5 mV is expected on the TPA6120a and max 100 uV times the gain. 7.3 mV is a bit much according to datasheets. How much do you have on AD8610 output?

Notice that THS6012 is the industry version with more detailed specs. Input bias currents may have some influence. Anyway 7 mV is not much.

Both transistors are dead.

The 27 V zener should also be dead. Check if you have max 27 V across it if you have supply voltage applied. Make sure you have a current limitation otherwise you will fry it. You can also do a diode test. RED wire on anode (ground) and BLACK on cathode. You should get 0.6-0.7 V.

Espirit wrote

Quoteheaveno
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Please find message attached.
Hi
Board 1
T1
B-E= 143mv
E-C= 40mv
C-B= 0.0-0.6mv

T2
B-E= .4v
E-C= 22.6v
C-B= 0.0-0.6mv

Board 2
T1
B-E=.623mv
E-C= 22.2v
C-B= 1.8mv-6.6mv

T2
B-E= .4v
E-C= 22.2v
C-B= 0.0mv-2mv

Both coils changed

Regards
James

Today got the TPA8610 and put it in. Now everything seems to be ok.

I measure 4,7 mV on left output and 7,3 on right. Between left/right out 2,6 mV.
What else should I check.

Also the Alps Pot 2712 10K is OK?

Thank you
Branko

It's really hard to tell why this happened. The first guess is soldering.

Desoldered TPA8610 and Pin 1, 2, and 4 are shortened right side seems ok. Will now order one for replacement.

What could have dstroyed it? could not find a reason on the board?

thx

Found a short (50 Ohm) between +12V and -12V in the left side! No short in all the small 805 parts around the regulators and the AD8610. Pins 1 to 4 of the TPA8610 set also short (about 25 Ohm).

Right side is different here. Maybe the TPA8610 is the problem? (was presolderd)

Should I try to desolder the TPA8610?

Desolderd Transformers and Rectifiers:

Rectifiers measure fine. Transformers give about 20.5 V AC out with 226 V in.

Where to look now?

Hi,

the things start to get worse :(

At the first start with 230 V I tried to check the Voltage at the rectifier out (around 21V) then had a short "spark" at the right channel rectifier +_terminal. But everything seemed to be OK?

Meassuerd Voltage at the output terminals (few mV). After a while the transformers started to got hot (72 °C) and voltage all around changed a lot?

Now when I check Voltage at the transformers fron below side I get 230 V in but only 6 V out (still soldered to board)?

Seems like I perforated the solder mask with my tiny meter probe and made a short (see picture below)

What to do next? desolder the transformers and rectifiers?

Thank you

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Tonight have build the Amp :)

Now would like to check it:

"Check the finished amp

Apply voltage again and check the output voltage. Measure the DC voltage at the output. It should be the specified offset voltage (see datasheet) and times the gain, 4 in this case. I got 78 uV(!) for AD8610 and 2 and 10 mV for the TPA6120 at the amp outputs. 10 mV is OK and won't harm the headphones."

Where and how do I measure the DC Offset for AD8610 and TPA6120?

Without anything connected I measure at the output Terminals  -1.83 V and +2.26 V

Thank you!

PS: The Transformers (Myra 44159) get quite Hot?