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Old 15th December 2011, 03:17 PM   #1201
PierreQuiRoule is offline PierreQuiRoule  Canada
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Rich - So the jfets look good. Back to the board then.

What are the voltages at the top and bottom of R9 when there is NO jfet installed at all? They should be the same and close to 20 volts.

Turn off power. With your ohmmeter, and NO jfet installed, verify that the resistors between each jfet and ground (R21 to R24) are indeed 10 ohm each.

If all is good, next verify consistency in your measurements. Solder ONE jfet and measure Q3 (all 3 pins). Remove the jfet, solder another one and repeat.

Pierre

Last edited by PierreQuiRoule; 15th December 2011 at 03:19 PM.
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Old 15th December 2011, 04:22 PM   #1202
richluvsound is offline richluvsound  United Kingdom
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R9 Top = 20.42 Bottom = 20.27

R21-24 are all 10R . As for the fets soldering .... I use Q6 position for each fet
i test in situe ?
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Old 15th December 2011, 04:26 PM   #1203
PierreQuiRoule is offline PierreQuiRoule  Canada
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Yes. In situ please.
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Old 15th December 2011, 05:47 PM   #1204
richluvsound is offline richluvsound  United Kingdom
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1) 7.09 mA

T, 3.61
M, 10.01
B, 3.22

2) 7.08 mA

T, 2.59
M, 6.79
B, 1.84

3) 7.01 mA

T, 2.38
M, 6.77
B, 1.51

4) 7.18 mA

T, 2.20
M, 5.03
B, 1.86

I don't understand why the first one was that way and the others dropped .

Rich

T,
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Old 15th December 2011, 06:08 PM   #1205
PierreQuiRoule is offline PierreQuiRoule  Canada
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Rich - Interesting. T, M, B means top, middle and bottom pin of Q3, correct? Something funny is going on. Let me chew on this for a while.

Do you think you could post a close up pictures of this area of the board (component side and solder side) ?

Pierre
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Old 15th December 2011, 06:21 PM   #1206
nar is offline nar
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Quote:
Originally Posted by PierreQuiRoule View Post
Rich - Interesting. T, M, B means top, middle and bottom pin of Q3, correct? Something funny is going on. Let me chew on this for a while.

Do you think you could post a close up pictures of this area of the board (component side and solder side) ?

Pierre
Pierre - yes, definitely there is something strange going on here. I'm puzzled

Let's wait for Rich pictures. At least, his camera works very nicely

Best,

nAr
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Old 15th December 2011, 06:21 PM   #1207
PierreQuiRoule is offline PierreQuiRoule  Canada
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nAr - Yes there definitely is a problem.

Got another idea. Wondering if the board is somehow applying voltage to the gate of the jfet.

Rich - Please would you short-circuit the input to ground, and re-measure Q3 (T, M, B) with one jfet in Q6? And please would you measure the gate (middle pin) of the jfet in Q6. It should be at 0 volts. If it is not, we may have found a problem.

Pierre
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Old 15th December 2011, 06:26 PM   #1208
nar is offline nar
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Quote:
Originally Posted by PierreQuiRoule View Post
nAr - Yes there definitely is a problem.

Got another idea. Wondering if the board is somehow applying voltage to the gate of the jfet.

Rich - Please would you short-circuit the input to ground, and re-measure Q3 (T, M, B) with one jfet in Q6? And please would you measure the gate (middle pin) of the jfet in Q6. It should be at 0 volts. If it is not, we may have found a problem.

Pierre
Yes, gate should be close to Ground

nAr
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Old 15th December 2011, 06:48 PM   #1209
richluvsound is offline richluvsound  United Kingdom
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with short across input , Q6 Gate 0 VDC

Q3, T = 17.49 VDC

M = 10.11

B = 17.36
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Old 15th December 2011, 07:10 PM   #1210
nar is offline nar
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The resistor left to the R8 (seen on top^) ; on the 2 sides, bottom solder joint of R looks bad

nAr
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