Made a mistake - need advice

Air · 8678

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Offline Air

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on: April 03, 2010, 09:18:44 AM
Was messing with my EFP III and when putting the shunt board back in miswired the B power supply and fried the 53.6 ohm resister. Smokes the resister it now measures +300 ohms but got the power off real quick. 2 questions, can I replace the resister with a 51 ohm (closest I have) and whet are the chances I messed up something else?
AS always, thx for any help. -Chuck

Chuck McCalment    Linn TT- Seduction (C4S), EFPIII, Parabees's w/ shunt reg and DC heaters. Nava interconnects, homebrew power and speaker cables,  Homemade three way & S8's w/ ribbons for Christmas.
a Technics RS1500 that needs a little love.


Offline Paul Joppa

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Reply #1 on: April 03, 2010, 11:02:12 AM
51 ohms is fine; it just sets the current into the shunt regulator.

To blow up that resistor you must have fed it way too much current, so the chances are good that something else was fried at the same time.

I see two choices:

1) you know the drill, check each transistor and LED for intact diode behavior - conducts one direction, not the other, base to emitter and base to collector for transistors. And of course measure the other resistors. I don't have a convenient test for the shunt regulator chip.

2) Spend a buck at Rat Shak for a 51 ohm resistor and give it the smoke test.

Paul Joppa


Offline Air

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Reply #2 on: April 03, 2010, 11:08:00 AM
Thanks for your time Paul. Had to buy about a million resistors in a package for $12.95 to find a 51 ohm value. Is there any chance this problem left the Shuntboard? should I look at the other two boards? Wiil report back after getting this sorted out.

Chuck McCalment    Linn TT- Seduction (C4S), EFPIII, Parabees's w/ shunt reg and DC heaters. Nava interconnects, homebrew power and speaker cables,  Homemade three way & S8's w/ ribbons for Christmas.
a Technics RS1500 that needs a little love.


Offline Air

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Reply #3 on: April 03, 2010, 11:29:55 AM
The shunt Board looks like the "A" Reg end of the board is supplied from the new "A" Mono power supply, with the other end of the Shunt Reg (the B end of the board)is supplied from B power supply.
If so I have something else wrong, the 53.6 ohm resister was on the A end of the shunt board, and I had the B power supply crossed?
I need to try working on my bottlehead gear at first light instead of late night after a long day.

Chuck McCalment    Linn TT- Seduction (C4S), EFPIII, Parabees's w/ shunt reg and DC heaters. Nava interconnects, homebrew power and speaker cables,  Homemade three way & S8's w/ ribbons for Christmas.
a Technics RS1500 that needs a little love.


Offline Paul Joppa

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Reply #4 on: April 03, 2010, 02:26:29 PM
Also, try not to assume we have been sensible.  :^)  The "A" end C4S feeds the "B" end shunt reg circuit, and vice versa. The wiring is easier that way, as long as you don't try to make sense of it!

Paul Joppa


Offline Air

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Reply #5 on: April 03, 2010, 03:59:00 PM
Big relief to know, will work on it now and be back later tonight with an update. Thx so much, probably saved me hours of looking in the apple tree for the strawberries. -chuck

Chuck McCalment    Linn TT- Seduction (C4S), EFPIII, Parabees's w/ shunt reg and DC heaters. Nava interconnects, homebrew power and speaker cables,  Homemade three way & S8's w/ ribbons for Christmas.
a Technics RS1500 that needs a little love.


Offline Air

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Reply #6 on: April 03, 2010, 06:30:03 PM
I have got everything back together. But have a problem with the resistance checks.

T12 @ 53.4K (should be 83K)
T21 @ 53.4K (83K)
T32 @ 53.4K (150K)
I have checked every wire to eat terminal and find nothing our of place.
I have checked the boards for damage and all check good (431 is Unknown)

it is odd they all read the same. Don't really want to smoke test it just yet. thought I'd ask the board first. _Chuck

Chuck McCalment    Linn TT- Seduction (C4S), EFPIII, Parabees's w/ shunt reg and DC heaters. Nava interconnects, homebrew power and speaker cables,  Homemade three way & S8's w/ ribbons for Christmas.
a Technics RS1500 that needs a little love.