I will try...
First Watt Amp requiring 24V DC are using transformer with an output voltage of 18v (AC, RMS). Peak output would be 18*sqrt(2)=18*1.414=25.45volts. Then the bridge rectifier is taking something like 1.6volts to give 23.85volts.
For F5 Turbo V2 https://www.firstwatt.com/pdf/art_f5_turbo.pdf 48Volts DC is needed, 36volts @transfomer output is suggest. (36*1.414)-1.6=49.3
So, if i were to using transformer + bridge rectifier + bank of caps, i would go with a 28volts @output transformer (28*1.414)-1.6=37.9 volts.
[26v output would give (26*1.414)-1.6=35.16, might be too low?. Bridge rectifier voltage drop increasing with current, one might use 2volts... hence 28v transformer]]
There are websites to do a betterwork than that i remember.
That's what i learned / think i have learned.
If mistaken, please tell me! [i might have misunderstood "how large"... If power rating, then yes, i have misunderstood]
First Watt Amp requiring 24V DC are using transformer with an output voltage of 18v (AC, RMS). Peak output would be 18*sqrt(2)=18*1.414=25.45volts. Then the bridge rectifier is taking something like 1.6volts to give 23.85volts.
For F5 Turbo V2 https://www.firstwatt.com/pdf/art_f5_turbo.pdf 48Volts DC is needed, 36volts @transfomer output is suggest. (36*1.414)-1.6=49.3
So, if i were to using transformer + bridge rectifier + bank of caps, i would go with a 28volts @output transformer (28*1.414)-1.6=37.9 volts.
[26v output would give (26*1.414)-1.6=35.16, might be too low?. Bridge rectifier voltage drop increasing with current, one might use 2volts... hence 28v transformer]]
There are websites to do a betterwork than that i remember.
That's what i learned / think i have learned.
If mistaken, please tell me! [i might have misunderstood "how large"... If power rating, then yes, i have misunderstood]
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I used a 300VA transformer, and your after ~36VDC, loaded for a Ship so 28VAC secondaries.
@Mark Johnson hello, I could use some troubleshooting suggestions with Missouri FE cards.
At power up with ~36V, R6 on one channel went up in smoke. I cleaned and inspected all the solder joints for bridges and cold joints and replaced R6 with another 47R resistor, and checked L1 to make sure it wasn't shorted (because it was easy to check). With the good channel, I hooked it to a variable bench power supply with inputs shorted, IC's in and stepped it up in increments to 36V. I never saw more than a 20mA draw, and I was reading about 27.5V at the top of R13/14 if memory serves.
With the bad channel, R6 replaced, even at ~24V in it was drawing 200mA, and the voltage at the top of R13/14 was about 14V. I didn't go higher than 24V.
All the diodes are oriented properly, the same on both channels, as are the MJE243 voltage regulators. Any suggestions as to what to look at next?
Thank you.
At power up with ~36V, R6 on one channel went up in smoke. I cleaned and inspected all the solder joints for bridges and cold joints and replaced R6 with another 47R resistor, and checked L1 to make sure it wasn't shorted (because it was easy to check). With the good channel, I hooked it to a variable bench power supply with inputs shorted, IC's in and stepped it up in increments to 36V. I never saw more than a 20mA draw, and I was reading about 27.5V at the top of R13/14 if memory serves.
With the bad channel, R6 replaced, even at ~24V in it was drawing 200mA, and the voltage at the top of R13/14 was about 14V. I didn't go higher than 24V.
All the diodes are oriented properly, the same on both channels, as are the MJE243 voltage regulators. Any suggestions as to what to look at next?
Thank you.
Remove ICs from failing Missouri board, hook the PCB up to a variable bench power supply, and very slooooooowly turn up the voltage until the bad Missouri board is drawing 69 or 70 milliamps. That'll cause R6 (47 ohms) to dissipate a quarter of a watt.
Oh by the way, if you can wind up the voltage all the way to 36 volts but the supply current stubbornly remains below 70mA: presto you have discovered the problem! One or both ICs were bad, or were socketed backwards.
With 70 mA flowing, lick your fingertip and touch each component in the Power Supply Filtering section of the circuit schematic diagram. Which one(s) are hot? Write their name(s) down.
With 70 mA flowing, use an accurate digital voltmeter to measure the voltages at the following seven important power supply nodes:
Oh by the way, if you can wind up the voltage all the way to 36 volts but the supply current stubbornly remains below 70mA: presto you have discovered the problem! One or both ICs were bad, or were socketed backwards.
With 70 mA flowing, lick your fingertip and touch each component in the Power Supply Filtering section of the circuit schematic diagram. Which one(s) are hot? Write their name(s) down.
With 70 mA flowing, use an accurate digital voltmeter to measure the voltages at the following seven important power supply nodes:
- Voltage input to Missouri at connector P5
- Voltage at the flywire loop of R6 -- this is the R6-C5 junction
- Voltage at the flywire loop of R9 -- this is the R9-R10 junction
- Voltage at the flywire loop of R10 -- this is the R10-D4 junction
- Voltage at the flywire loop of R11 -- this is the R11-R12 junction
- Voltage at the flywire loop of R12 -- this is the base of Q2
- Voltage at the flywire loop of R13 -- this is circuit node VTOP
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Well, um, was doing my homework, and found that I couldn't get a stable 70mA draw- the applied voltage to keep the defective Missouri board drawing 70mA had to be adjusted upwards every 30 seconds or so. Nothing was getting hot that I could feel. I kept chasing voltage readings across test points until suddenly the electrolytic filter capacitor C12, which had been installed backwards, popped. So there you have it.
With C12 replaced, the defective Missouri board draws about 10mA with the ICs out, and a little under 30mA with them in. Same for the other channel. With 36V in the top of R13/14 measures 27.55V which is a familiar reading from other cards.
Thank you Mark for the excellent troubleshooting guide.
With C12 replaced, the defective Missouri board draws about 10mA with the ICs out, and a little under 30mA with them in. Same for the other channel. With 36V in the top of R13/14 measures 27.55V which is a familiar reading from other cards.
Thank you Mark for the excellent troubleshooting guide.