LC Audio Zappulse 2.1 Issue

[Lars Clausen]

And both modules are doing the same?

Both -35V out?

 

[john65b]

Now that I have changed the burnt resistor on the one module from 1K ohm to 68 ohm (I did not have an 82 ohm available) the DC at output is more like positive 10V.

I can get an 82 ohm resistor and try. But still have no sound at the output with the 68ohm.

The module with 1 ohm is still at -35V on output.

 

[Lars Clausen]

what have you tied the gate drive supply to?

Have the modules been working in your setup at one time?

 

[john65b]

The modules worked at one time.

I beleive I had misconnected the power GND and -V rail a while back. Saw some smoke, so I disconnected the module. The only damage I saw was the 80 ohm resistor in front of the caps. They were charred, so I removed them. I was unable to dterermine their value. I sent an emauil to LCAudio, and afetr a few emails they said it was 1K, but I knew they were thinking of another resistor.

None of the MOSFETS are not shorted to each other. Both square caps seem to be fine (show 22uf on my LC meter). the Rifa caps below also seem fine (caps not open, or shorted). On the Rifa caps below, the two closest to power/output connections shoe .22uF in circuit and teh back ones show 2.2uF in circuit)

What have I connected to the Gate Drive Supply? Sorry, I don't understand. All connections to the modules are +V, -V, V GND, Sig in, Sig GND, Out, Out GND.

I have no other connections on the modules.

 

[Lars Clausen]

OK, it's likely the modules are damaged from the supply break.

You should measure the Vgate on the IRF640N mosfet. It should be around 12V. (On the Source). Be careful not to short anything with your meter.

 

[john65b]

OK, measure the three MOSFETs. A MOSFET that is not shorted can still be bad. This is what I was hoping.

MOSFET Tab (or drain) to Source Pin should be 12VDC with no connection on input or output...Got it...will try tonight.

I just ordered six IRF640 MOSFETS the other day thinking this is what needed to be replaced. Hopefully this will be the issue.

Mr Clausen, I really appreciate your assistance.

I have a Tripath TA3020 Amp, a UCD400 amp and was hoping to get the ZAP working so I can do my own personal review.

Thanks again.

 

[john65b]

Here are the voltages I get across the MOSFETS - all voltages are grounded to tab/drain

Module #1
MOSFET #1

Source -23.5V (+V Rail Side)
Gate -23.5V

MOSFET #2

Source -43V
Gate -43V

MOSFET #3 (-V Rail Side)
Source -22V
Gate -18.5V

Module #2

MOSFET #1(+V Rail Side)

Source -70V
Gate -70V

MOSFET #2

Source 0V
Gate +12V

MOSFET #3 (-V Rail Side)
Source -23V
Gate -19.4V

All six appear bad? Maybe MOSFET #2 on Module 2 is OK?

 

[john65b]

After thinking about it further, I do not believe I miss connected the GND and -V rail, but either the GND or -V rail may have not been securely soldered onto the connection. Would this cause the problem losing the GND or a rail?

Anyway, the Voltages should read:

Module #1
MOSFET #1 (+V Rail Side)

Source -23.5V
Gate -23.5V

MOSFET #2

Source -43V
Gate -43V

MOSFET #3 (-V Rail Side)
Source -22V
Gate -18.5V

Module #2

MOSFET #1(+V Rail Side)

Source -70V
Gate -70V

MOSFET #2

Source 0V
Gate +12V

MOSFET #3 (-V Rail Side)
Source -23V
Gate -19.4V

 

[Lars Clausen]

It's a bit hard to troubleshoot from these measurements, especially since they are taken from source to drain etc. and in uneven order.

Could you repost the measurejments, this time with GND as reference, and starting from the top V+ mosfet?
That would make it somewhat clearer i hope.

Thanks

 

[john65b]

Lars,

Yes, I will retake those measurements from GND.

Sorry, and thanks again for the help.

 

[john65b]

OK, once again Voltages referenced from Power Ground:

Module 1

MOSFET #1 (V+ Side)
Vs = +10V
Vg = +10V

MOSFET #2
Vs = -36.3V
Vg = -36.3V

MOSFET #3
Vs = -24V
Vg = -20.2V


Module #2

MOSFET #1 (V+ Side)
Vs = -36V
Vg = -36V

MOSFET #2
Vs = -36.5V
Vg = -24.3V

MOSFET #3
Vs = -24.2V
Vg = -20.4V

Hope this helps.

 

[ozangazi]

i think you must clear fet pins..Soldier relic is much unfavorable for low signal and high frequency applications..

 

[john65b]

i think you must clear fet pins..Soldier relic is much unfavorable for low signal and high frequency applications..

Clear FET pins? I do not understand.

I have received six new IRF640 MOSFETs. I can replace them if need be.

I also took these voltages with no connections to input and output. Was I supposed to have a dummy load across the output for these Gate/Source/Drain voltages to be real/accurate?

Sorry for all the lame questions.

I am beginning to think these modules are KAPUT... thinking of getting another UCD400 or finish my AMP2. But then again I need another amp ilke I need a hole in my head.

 

[ozangazi]

i mean,clean solder paste remains after soldering ...

Sorry for poorly english

 

[john65b]

Currently, there is no solder across pins - the voltages I have are from a stock, unmodified module.

I may replace the MOSFETs and will remember to keep them clean.

Thanks