F2/ F2J trouble shooting help

[kinku]

Hi Geeks,
After two years of service my F2J clone stopped working. Unsure what happened but possibly a line level or lightning issue, both my auralic aries mini and F2J stopped working. Mini analog audio outputs not working and no output from F2J. Easiest thing to do will be to replace three transistors but I do not want to sacrifice my SJEP120R.
How can I figure out if my JFET still working?

 

[Zen Mod]

care to post ref. sch and some measurements, if you did them?

 

[kinku]

Hi Zen mod. I do not remember the trouble shooting protocol. Could you please help?
I followed the exact schematic

FIRST WATT

What all voltages I should check?

 

[rhthatcher]

I just rebuilt one of these for a guy, and it's in the box waiting for him to return from a trip before I ship it..

Take some pix of your amp to share.

See the schematic below. What voltage to you get at the red circles? 24V and ~12V? Start there first and report back.

The amp I built used an Avel Lindberg Y236651 250VA 18+18V transformer, and I was getting 24.10V from the PSU. You set P1 to get 1/2 of PSU voltage at the red circle in the middle once the amp has warmed up for an hour. So in my case I set to 12.05V.

 

[kinku]

Thanks rhthacher.
Input voltage 25.1V
And 25 V At + C2
cap

 

[kinku]

Board pic

Here are some boards pic

 

[kinku]

The amp I built used an Avel Lindberg Y236651 250VA 18+18V transformer, and I was getting 24.10V from the PSU. You set P1 to get 1/2 of PSU voltage at the red circle in the middle once the amp has warmed up for an hour. So in my case I set to 12.05V.

I have the 18V +18V secondary trany
I see, something changed with Biasing but why would it happen? All of a sudden?
I biased it perfectly with an oscilloscope two years ago!!

 

[chromenuts]

Hi Kinku

My F2J monoblocks are currently disconnected from my system because the cooling fans I built into the cases were getting too noisy for my liking.

I ordered some better quality replacements and will either be opening the cases up to replace them or pull them out all together and make babysitters for under the cases so the fans can be cleaned or changed easier if needed.

I think our amps are built with the same boards and components for the most part.

If you need me to test voltages at different points in the circuit for reference I could probably help.

 

[Dennis Hui]

What voltages do you measure across R16, R7 and R23?

 

[kinku]

R16,R17 0.7 mV
R23 0.5 mV

 

[kinku]

Hi Kinku

My F2J monoblocks are currently disconnected from my system because the cooling fans I built into the cases were getting too noisy for my liking.

I ordered some better quality replacements and will either be opening the cases up to replace them or pull them out all together and make babysitters for under the cases so the fans can be cleaned or changed easier if needed.

I think our amps are built with the same boards and components for the most part.

If you need me to test voltages at different points in the circuit for reference I could probably help.

That would be nice of you! What are you getting voltages for these R17 and R23

 

[chromenuts]

Hi kinku

Sorry, I got distracted with something after supper last night.

I’ll open up an amp this morning and take measurements.

 

[kinku]

I am pretty sure it is the change in Biasing as it should be half the voltage at the point RHthacher indicated. It was half the voltage before but not sure why it drifted ? Is it normal ?

 

[Zen Mod]

there is no significant current through output vertical , if output node is practically at rail potential, so no use of measuring voltages across R16/17

fist thing is to check voltage at Q1 gate , that'll confirm fucntionality of P1

if there is 1V5 or so, it's time for pulling both Qs out and check - first with diode test, then with anything else - either with modern measure-it-all Gizmo or in proper mosfet check jig

one more thing:

is same problem in both channels - I mean - no sound and both measuring the same (at output node) ?

 

[chromenuts]

Hi kinku

I opened up one of my F2J.

After a few minutes from power up I measured a few times to confirm.

Across R17 I measure .61 V DC

Across R23 I measure .21 V DC

Let me know if I can be of any other help.

I will try and keep an eye on your progress.

 

[Zen Mod]

while it's open , what's voltage at Q1 gate?

 

[kinku]

Mine reading 0.33Vand 0.242 V at both SJEP120R (Q1)Gates wrf to power ground.
And yes both Chanel behaving the same.

 

[chromenuts]

Processing...sorry gents, still in midst of morning routine and looking up data sheet and schematic to make sure I measure properly...

 

[chromenuts]

I get 3.14 V DC measured at gate pin mounting point indicated by red arrow in pic.

My negative probe was on signal ground of board.

 

[Zen Mod]

Mine reading 0.33Vand 0.242 V at both SJEP120R (Q1)Gates wrf to ground.
And yes both Chanel behaving the same.

check trimpots