F5 power amplifier

[acumos]

sorry, you would say to put the low voltage from the battery to the whole board or only to the led pins?

 

[bcmbob]

You need to confirm two separate things: 1. The LEDs are good and connected correctly with an independent power source . 2. The circuit on the amp is supplying the correct voltage to light them - again with correct polarity. When you have that info, then you can proceed to the next steps in trouble shooting.

 

[acumos]

1. The LEDs are good and connected correctly with an independent power source .

no the leds of the f5 boards are bad.

 

[bcmbob]

Hopefully there is a Radio Shack or similar local supplier nearby for replacements - or maybe you have some from other projects.

 

[acumos]

Hopefully there is a Radio Shack or similar local supplier nearby for replacements - or maybe you have some from other projects.

in this step I don't care about the lights. So can I test only one f5 board (assuming that all is early is ok) with an 9v battery or I can go with dim bulb tester and 220v?

 

[bcmbob]

You are above my pay grade now - others will assist you from here on. I'll put out a couple PMs. Hang on a few minutes.

 

[nkdk]

@acumos do you have isolations pads under the powermos,and are they okey.
check with a multimeter
nkdk

 

[acumos]

yes

 

[bcmbob]

One question I'm not sure of is if the LED serves more than one function in the circuit. Even if you proceed (I wouldn't without the LEDs functioning) would the readings be useful. I just don't know. You may be anxious to continue but I'd wait for a little more information. The Gurus will show in time.

 

[acumos]

ok I tried connecting the f5 boards and now the bulb flashes and dims off. Now I've turned the P1 and P2 and I measure at R11 and R12 0 ohm. But I can't reach more than 0.03 volts.
At the external legs of the two mosfet I have 3.0 and 3.5 volts

 

[acumos]

One question I'm not sure of is if the LED serves more than one function in the circuit. Even if you proceed (I wouldn't without the LEDs functioning) would the readings be useful. I just don't know. You may be anxious to continue but I'd wait for a little more information. The Gurus will show in time.

I didn't see your post

 

[bcmbob]

You can't get the measurements correct with the bulb attached. If all else looks safe - remove the bulb tester and try the adjustments again.

 

[acumos]

You can't get the measurements correct with the bulb attached. If all else looks safe - remove the bulb tester and try the adjustments again.

I've removed the bulb. But nothing changes. At r11 if I put the probes directly on the resistor base I have 0.06v, in the pcb hole 0.015v. If I put the probe in V+ and V- in the f5 board I have 47v.

 

[bcmbob]

Here is another build guide with a slightly different explanation of the testing phase. It appears you are getting the combined rails with the 47V reading.

 

[pchw]

I've removed the bulb. But nothing changes. At r11 if I put the probes directly on the resistor base I have 0.06v, in the pcb hole 0.015v. If I put the probe in V+ and V- in the f5 board I have 47v.

Measure form + to ground and - to ground, 47V between + and - is about right, keep mind the PS is Plus <-> ground (0) <-> Minus, 23 <-> 0 <-> -23 will be 46V in difference between 2 "extreme".

 

[acumos]

Measure form + to ground and - to ground, 47V between + and - is about right, keep mind the PS is Plus <-> ground (0) <-> Minus, 23 <-> 0 <-> -23 will be 46V in difference between 2 "extreme".

Ok. But it seems I can't have voltage (or measure it) at r11 and r12. Instead between source-gate and drain-gate (q3 and q4) I have +-24v
Between R4 and R3 I have 0 volt

 

[pchw]

If there is no measurable voltage across R11 and R12 (the soruce resistors), then there is no current passing through the output devices, meaning they are off. If R3 and R4 have zero volt, it suggests the pots (P1 and P2) are shorted, i.e. they are turned to the extreme end and have no resistance. Did turn these 2 pots? It is pssobile that the bias is not set correctly yet.

Another reason that there is no voltage in R3 and R4 is the jfets are dead. I hope this is not the case.

 

[acumos]

Now I've blown another fuse. I think I have to check every transistor cause at first I've mounted Q5 and Q6 in wrong way. How can I do this?

 

[acumos]

nobody?

 

[pchw]

Given my limited eqiupments and knowledge, I always desolder the transistors out of the PCB or desolder enough to isolate the devices for testings. To test the devices, you simply perform an Idss or Vgs measurement. If a device is bad, the numbers will be total off.