Switching the F5T on
With regards to the connections from the amp board
1. Speaker out goes to Red terminal of speaker out.
2. The PGND which is right below the speaker out in the center goes to the black terminal on the cabinet.
3. +ve, -ve and pgnd 2 go to psu board.
4. RCA input needs to be soldered in
You are correct Pandu.
Here are steps -
Start with all disconnected - transformers, Rectifier Board, PS filter and F5 turbo Amp boards.
Connect them one by one, step by step after power down and disconnecting mains from wall. No hurry, its result day of long preperation and hardwork.
1. Mains Supply (Caution: This is deadly, be careful)
Checking:
Check mains wire to switch, through fuse and transformers. Output wires (secondaries) of transformers are taped and secured for avoiding short circuit.
Mains wire - live (L) must not short to chassis, neutral(N) and earth ground(E).
Connect as below and then power ON:
Connect primary of each transformer and use >200VAC range on DMM to check output voltage on secondary. If measures 24V then move ahead.
Power off and disconnect mains wire.
Connect 100W bulb tester in series of mains (L) Live wire and proceed.
2. Rectifer Board:
Checking:
PCB copper, heatsink of diodes is not shorted to any wire, chassis or any metal nut-bolt. Verify all [~] marked pins are not shorted to [+] and [-] marked pins. Also [+] and [-] not shorted to each other.
Connect as below and then power ON:
Connect all secondary pairs from transformer to AC input points on the PCB and power on.
Light bulb on mains (L) wire should flash for moment and goes off.
Change DMM to DC 200V range.
Measure voltage on [+] and [-] point of rectifier board. If its 34-35V then move on. You are correct till this point.
Power off and disconnect mains wire.
3. Filter board:
Checking:
Verify all pins of +V and -V are well isolated from mounting nut-bolts and chassis. Polarity of bigger caps are in correct direction, matching with supply output polarity.
Connect as below and then power ON:
Connect 4 X ([+] & [-]) from rectifer to PS filter board.
After power ON Light bulb on mains (L) wire should flash for moment and goes off. If keeps glowing then disconnect power immediately.
Keep DMM to DC 200V range. Measure output voltage wrt GND toward output of PS filter board. Unloaded voltage 34-35VDC.
Power off and disconnect mains wire. Wait for caps to discharge for 5 min.
4. Each amplifier board:
Checking:
- Check MOSFETs are well seated onto their heatsink and tightly attached to heatsink through mica and paste. No air gap in between mating surfaces of MOSFET and heatsink.
- PCB is well secured and part leads are not touching to heatsink.
- Input and output wire are not shorting to anywhere except intended connectors - input (RCA - PCB ) and output (Banana post - PCB).
- Those green NTC are touching MOSFET body and stable. You can put little heat paste between their body contact points.
Important: Change DMM to 2K? range.
Verify 0 resistance across each 1K? resistance near 5K? trimpot P1, P2. You will listen clicking sound from trimpots, you have to stop turning its screw. Mark the direction of turning screw (-) in which you made its resistance zero. That way you made bias also zero. Remember opposite direction is +ve. Mark it if possible. User marker pen. You are ready to go.
Connect PS wire with correct polarity and verify.
Powering on:
DMM batteries are new and leads are okay, not loosely connected.
Connect DMM with mV range to source resistors at extreme. You can use 2 DMM (if possible) each on P-side and N-side. No problem with having only one on either side. Use other DMM on output with mV range.
After power ON Light bulb on mains (L) wire should flash for moment and goes off. If keeps glowing then disconnect power immediately. Also if you see high voltage or max(1 . ) in any of DMM then stop, disconnect power immediately.
If you are okay till this point then power off mains, remove light bulb tester and continue henceforth.
Biasing:
Now turn half rotation in +ve direction each time in each side till you see measurement in any of DMM. Hence forth turn half rotation at one side of preset and null output to zero mV by setting other side of preset.
Settle at 100mV across source resistance, let it settle for 1 hr. Take a break. Observe heatsink and MOSFET body temperature, both are passing 10sec touch test.
Repeat above step till 200mV and again wait-check for 1 hr.
Same way till 300mV.... till 375mV ( that's my limit, your limit is till heatsink pass 10sec hand touch test)
After it is stable, cover the top plate and wait for another 1-2 hrs. Observe output offset and source voltage. If all stable then you are done.
For -ve offset rotate (-) side trimpot in (-) direction, for +ve output offset rotate (-) side trimpot in (+) direction. If voltage across source resistor increases ( that means bias increased) then decrease both trimpot gradually in opposite direction you increased.
Best of Luck!
). Slowly it's opening up nicely(almost 20 hrs running time till now). What is worth mentioning that at a medium to low volume the reproduction is excellent. Let's hope it gets better & better as time passes.
