Help Blackstar Club HT-40

[fabiofubeka]

I found a SMD diode shorted, can anyone help me with the value of it?
BlackStar HT Club 40 - somebody has the scheamtic?
D121

thanks

[Jazz P Bass]

Have you attempted to contact Blackstar?

Often times the values are not printed on there schematics.

[teemuk]

I wouldn't count on Blackstar being too helpful....

Can you figure out the purpose of the diode? Is it in signal path, in power supply, on a FET gate? What is its function? You should be able to tell the function without even knowing the diode type. Is it in some critical circuit like SMPS that could be sensitive to parameters like recovery speed, are there other diodes around that obviously share the same function? A little snooping of the circuit can get you pretty far alone...

Is the type really important? I'm not familiar with HT-40 but in an amp like the HT-5 most diodes, obvious rectifier diodes excluded, were either FET switch gate diodes, zener clamps to clip voltage surges on signal path or just ordinary signal clipping diodes. Practically 90% of them were generic 1N4148 and not overly critical regarding what other silicon diode replaces them.

[fabiofubeka]

I removed the PCI diode is normal.
The pre-amp is OK, Now I'm going to output Tubes. Do not have audio output.
I will test the 2 EL34, not replace because I'm currently without EL34.

[Enzo]

Was hard to find.

Click your channel change button to the other position and see if the diode un-shorts. If you are using the footswitch, click its channel change button or just unplug the pedal.


D121 is a dual diode, the amp uses a bunch of them Two diodes in series as a clamp. Peavey wired clamp diodes across input and out put jacks for years. This one is on a channel switch line. The junction of the two is the switch input, the free ends go to +3.3 and to ground.

[Enzo]

No sound? Check voltages at the power tubes and the preamp tube. Power tubes need high voltage on pins 3 AND 4, some reasonable bias on pin 5, and a path to ground from pin 8. You seem to have a bias test point, which is a 1 ohm resistor to ground from the tube cathodes. So any DC across that is evidence the tubes are conducting.

Likewise the preamp tubes, is there high voltage on the plates - pins 1 and 6? And a volt or two on the cathodes - pins 3 and 8?


And all the tubes, are the heaters glowing?

[fabiofubeka]

Thanks Enzo.

The pre amp is perfect, pre Valves OK / Power
But I found the TR2-STK830 leaking.
replace the two STK, but is leaving the low noise and audio.
Attached photo with the measures. 47K resistor is a correct 90V and 360V other side?

[Jazz P Bass]

Here is a power supply schematic for the HT-1.

[52 Bill]

47K resistor is a correct 90V and 360V other side?

Are you sure that both resistors are 47K? One looks like it is a 470R.

I would expect to see similar voltages on both resistors.

[blindboybenton]

Blackstar in the uk are very helpfull. They wont give out there schematic, but tell them whats wrong and they will help.

BBB

[fabiofubeka]

Bill,

they are 47K,

Which seems to 470R, The IRF830 entered to flight.
Measure it out PCB is OK.
IRF830 works too hot in my opinion should have thermal heatsink.

Has exhausted my possibilities to check for faults.

[mozwell]

Not sure if these will help.... one of these may be close enough though

[Jazz P Bass]

Moz, the links are dead.

Zip them.

[mozwell]

here you go Jazz

[fabiofubeka]

Thanks, mozwell.





The pin 1 IRF830 gate (yellow) enters the TR1/TR2 signal.
TR2 signal does not arrive at the gate, this red square FET19 seems to me that he is arriving at the gate TR2 feedback.

Not fuse breaks down, maximum output power of 1 watt.