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Old 5th December 2008, 04:26 AM   #11
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i replaced one 2a on the board went to measure the voltage on the gates 1 side theres no voltage at all wondering what the problem might be
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Old 5th December 2008, 04:30 AM   #12
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What's the DC voltage on pin 9 of the 494?

Pin 10?

The base of the 1a drivers?

The collector of the 1A drivers?
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Old 5th December 2008, 04:59 AM   #13
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i measured the voltage on all the pins of the 494

Pin1-- 0 volts
pin2-- 4.73
pin3-- .06
pin4-- .10
pin5-- 1.53
pin6-- 3.43
pin7-- 0
pin8-- 13.17
pin9-- 5.06
pin10-- 5.67
pin11-- 13.17
pin12-- 13.17
pin13-- 5.02
pin14-- 5.02
pin15-- 5.02
pin16-- 0

all reading are with just remote wire and ground hooked up.

Also on the 1a drivers they are showing no voltage on any of them
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Old 5th December 2008, 05:11 AM   #14
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I don't have the schematic diagram for this amp but if it's like virtually every other Rockford amp using the 494, the collector of the 1A driver transistors should be directly connected to pins 11 and 12 of the 494. Find the open trace or feedthrough and repair it.
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Old 5th December 2008, 05:48 AM   #15
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ok 1 quick question on this amp is it common or do i have something shorted the power supply fets are mtp75n05hd.

the drain and the source of the fets show 0 ohms between them like they are connected together i took them out and touched the pads.

i still get 0 ohms between the drain and source on the pads is this normal or is something shorted?
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Old 5th December 2008, 05:57 AM   #16
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0 ohms isn't normal.

It could be due to a shorted transformer winding. Clamp your meter probes in the B+ and ground terminals (nothing else connected to the amp). With the meter set to diode check or continuity (wherever it beeps when the probes are shorted), twist the transformer. Does the meter go from showing a short to showing something closer to an open circuit?

If not, the windings may be welded together or have too much pressure between them to break the connection between them when twisting the transformer.

If you're absolutely sure that you don't have a short between the pads on the FETs and the FETs are not defective, pull the transformer (or at least the 4 wires on the secondary. If the short is through the transformer, the short between legs 2 and 3 of the FETs should clear.
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Old 5th December 2008, 06:49 AM   #17
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thanks perry the transformer is junk . hooked the power and ground probes up to the terminals and it is shorted. turning twisting doesnt help at all the ttransformer is junk.

wondering if this amp is worth fixing ?? or is it a parts amp? any advice would greatly be appericated
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Old 5th December 2008, 07:09 AM   #18
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You can rewind the transformer. Do you have a dial or digital caliper?

Before you do that, you should get a good drive signal to the FETs.
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Old 5th December 2008, 03:34 PM   #19
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does anyone know of anyone who rewinds transformers??

Gonna be honest with u i dont have the first clue on how to do it
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Old 5th December 2008, 05:29 PM   #20
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All you have to do is...

Measure the wire so you know what gauge to buy.

Buy it from eBay, Amidon, Surplus Sales of Nebraska...

Remove the windings from the core counting the number of windings and paying attention to the way they're laid down on the core. Photographing it from several angles before removing any windings will help you to remember the layout.

Replace the windings with new wire.



If you don't want to rewind it, Check with Rockford. I think most of their transformers are in the $25-30 range.
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