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Old 19th November 2012, 04:01 PM   #8531
Doug R is offline Doug R  United States
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Oops, forgot:
40 V in, 3.5 V out regardless of pot setting.
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Old 19th November 2012, 04:05 PM   #8532
Salas is online now Salas  Greece
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Do you have a spare Q2?
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Old 19th November 2012, 04:07 PM   #8533
Salas is online now Salas  Greece
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Are the Leds lit and equally bright now? What are the drops across R4, R5?
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Old 19th November 2012, 05:00 PM   #8534
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Sorry off topic cant post picture on PM
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Old 19th November 2012, 05:03 PM   #8535
FdW is offline FdW  Netherlands
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Quote:
Originally Posted by Doug R View Post
FdW: I don't understand.
If you remove the white areas of the PCB then air can move freely along the fins of the heat sink and then it will be able cool better.
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Old 19th November 2012, 05:29 PM   #8536
Doug R is offline Doug R  United States
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I'm back.

I misspoke earlier; It is actually the first LED that looks dimmer. Each drops 1.8-1.9 volts. 5.65 V all together.
R4 shows 20.5 V drop.
R5 shows 0.6 V drop.

Yes I have a spare Q2.

FdW: got it now thanks. that makes sense.

Doug
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Old 19th November 2012, 05:31 PM   #8537
Salas is online now Salas  Greece
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Originally Posted by Bksabath View Post
Sorry off topic cant post picture on PM
Sandro, cheers mate! That hard to find strip will come handy for my TSSA I gather stuff for.
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Old 19th November 2012, 05:38 PM   #8538
Salas is online now Salas  Greece
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Quote:
Originally Posted by Doug R View Post
I'm back.

I misspoke earlier; It is actually the first LED that looks dimmer. Each drops 1.8-1.9 volts. 5.65 V all together.
R4 shows 20.5 V drop.
R5 shows 0.6 V drop.

Yes I have a spare Q2.

FdW: got it now thanks. that makes sense.

Doug
Q3 change fixed a number of voltages. Before changing Q2 which is inline loading it and if there is a hit in the error amp they form they usually die together, please look is there completed resistive path from Q5's drain through R7 and trimmer to V+ force AND sense when not tied together at a dummy load? What value is the dummy load again?
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Old 19th November 2012, 06:06 PM   #8539
Salas is online now Salas  Greece
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* We want to read some kOhm from Q5 & R7 node to +sense and open circuit to +force when those two wires don't meet each other. Then by turning the trimmer those kOhm to +s should be changing so we know the trimmer is alive.
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Old 19th November 2012, 06:40 PM   #8540
Doug R is offline Doug R  United States
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AAARRRGGGHHHH

OK. Replaced Q2 before I got your last message Salas.
Vin now reads 21 V instead of 40. (Voltage sag??) Diodes read OK in raw supply.

Anyway, Q1 now gets warm. Q4 still cold.

Pot resistance measures 0 to 4.7 kohm.
Q5/R7 node to Force (+) is big, about 8 megohm or OL.
Q5/R7 node to Sense (+) goes from 3.3 kohm to 8 lohm depending on pot setting.

V drop across R4 is 20.4 V
V drop across R5 is 0.55 V
Vdrop across R7 is 2.7 V
V drop across R1 is 2.2 V

Vin about 21 V
Vout with load (500 ohm) is 3.5 V
Vout with no load is 10.8 V

Q1 G to S = 3.3 V
Q4 G to S = 3.4 V

Q2 G to D = 3.4 V
Q3 B to E = 0.7 V
Q5 G to D = 0.7 V
Q6 B to E = 0.6 V
Q7 B to E = 0.54 V

What next boss?
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