I am getting around 52VDC on the output of the raw psu, what value of RD/link should I buy to bring it down to acceptable levels?
Also, my rega turntable has the ground connection going through the left channel ground. How should I connect the grounds on the case?
Also, my rega turntable has the ground connection going through the left channel ground. How should I connect the grounds on the case?
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I wired 2 10ohm 5W in series on RD/Link and I only get a drop to around 50.2 unloaded, can I connect that safely to the phono boards? I would have to wait until tuesday to get to the store and buy new ones.
Unloaded does not count. When loaded you will see a good drop. Its safe because done before.
Something strange is happening. I am getting around 34V between rail+ and ground on one of the boards, but only 18VDC on the other. DC on the raw psu is around 44V on the one giving 33V and around 42V on the one giving 18V
Look if there is too weak Idss Q3x in the low regulator or a bad Q4x Q6x
If with simply higher value R3x the rail voltage can be adjusted higher then its too weak Q3x
If with simply higher value R3x the rail voltage can be adjusted higher then its too weak Q3x
Well, now I got magic smoke from the led string near the DC IN. There was a loose piece of wire underneath the raw psu, it must have shorted something. No more light and the 2W resistor got very hot. Disconnected everything and I'm done for today.
Tomorrow I'll start by replacing the LED's and check if Q2X is still working and after that check Q3X.
Tomorrow I'll start by replacing the LED's and check if Q2X is still working and after that check Q3X.
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P.S. You can try the LEDS before desoldering just with the DMM in diode mode if its capable of turning on an LED or with a 9V battery by quickly trying to light them up
I replaced the LED's and the sk117 on Q2x. It has an idss of 3.74mA
R3x is 9.1Kohm
r6x is 27.5ohm
fired up and still getting 20V on the "faulty board".
Is 42VDC out of the raw psu enough for the regulator to work correctly?
R3x is 9.1Kohm
r6x is 27.5ohm
fired up and still getting 20V on the "faulty board".
Is 42VDC out of the raw psu enough for the regulator to work correctly?
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allowing for a nominal 7Vdrop across the regulator, then a 42Vdc allows upto 35Vdc at the output.
But 42Vdc Input is very high for a 20Vdc regulated output.
The Vdrop will be 22V and that generates a lot of heat.
The CCS mosFET has to dissipate most of that heat.
Have you killed the input mosFET?
One of the tests I carry out is to short the output (0volts output) and using a Variac increase the input voltage all the way to 253Vac (the UK's maximum supply voltage) and check that even though the CCS gets absurdly hot, it survives.
When the output short is removed the circuit returns to normal operation instantly.
For me this is a basic test of survivablity.
But 42Vdc Input is very high for a 20Vdc regulated output.
The Vdrop will be 22V and that generates a lot of heat.
The CCS mosFET has to dissipate most of that heat.
Have you killed the input mosFET?
One of the tests I carry out is to short the output (0volts output) and using a Variac increase the input voltage all the way to 253Vac (the UK's maximum supply voltage) and check that even though the CCS gets absurdly hot, it survives.
When the output short is removed the circuit returns to normal operation instantly.
For me this is a basic test of survivablity.
I am suposed to get around 36V DC in the regulator, I am only getting around 20 so I'm trying to figure out with Salas' help what is wrong with the circuit of one of the boards.
The other board is working correctly and there are exactly the same parts in each one.
The other board is working correctly and there are exactly the same parts in each one.
Yes it is, but something maybe is dragging this raw DC rail a little lower than the 44V other
20V tops is little for 9.1k R3x it would take to chance on a lowest GR range Q3x sample. Do your checks. Is Q3x barely pulling because there is no good Vbe on Q4x for instance? Less than 0.6V? Is Q5x really biasing it? What is the VGS reading on Q6x? If all semis check well then higher R3x will give higher Vout and its just a matter of Q3x IDSS. Also make sure that the voltage drop across R1x indicates about 100mA.
20V tops is little for 9.1k R3x it would take to chance on a lowest GR range Q3x sample. Do your checks. Is Q3x barely pulling because there is no good Vbe on Q4x for instance? Less than 0.6V? Is Q5x really biasing it? What is the VGS reading on Q6x? If all semis check well then higher R3x will give higher Vout and its just a matter of Q3x IDSS. Also make sure that the voltage drop across R1x indicates about 100mA.
I'll need to read that a few times. I'll try to compare readings between the good board and the bad one to see if I can find where is the faulty part.
I'm at work right now, I'll do that in a few hours.
I did some resistance measurements to check for continuity and one thing I noticed was that on the working board I got continuity from Q6x heatsink to ground. The bad board didn't show this continuity.
Q6x drain is indeed supposed to be at ground. Its sink should also show ground when there is conductivity between that MOSFET's tab (drain connected inside) and the sink metal. It does not need insulation for this circuit's purposes and the heat transfer is better without insulation when not needed. On the other hand Q1x's sink should be in continuity with Vout Rail +. If the screws are plastic and the anodizing perfect at the mating area maybe it prevents continuity but its indifferent to have continuity or not to the sinks in this design.
Here are some measurements:
ON Q2X - 37.55V between drain and gate and drain and source
VGS on Q6X - 3.29V
VBE on Q5X -0.615V
Voltage across R1X - 1.55V
ON Q2X - 37.55V between drain and gate and drain and source
VGS on Q6X - 3.29V
VBE on Q5X -0.615V
Voltage across R1X - 1.55V
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