Concord CA75.2 relay problem? - diyAudio
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Old 12th January 2012, 03:52 PM   #1
Mote is offline Mote  Estonia
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Default Concord CA75.2 relay problem?

This amp powers up, does not draw current but the relay does not click.
Power LED lights up, rail voltages are produced and present on all output transistors.
Relay is DH2U, it has 6 pins, 4 pins connect emitter resistors to speaker terminals. Other 2 pins are then those which should turn the relay on.
On one of those pins voltage to ground is 0,9V, on other pin: 11,3V.
Voltage across pins is quite big then, so I assume that relay is supposed to engage.
Can I remove the relay and install jumpers to connect output transistors to speaker terminals and check if I can get audio out of the amp?
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Old 12th January 2012, 04:11 PM   #2
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If you have 12V across the relay coil, this indicates that any protection circuitry has allowed the relay to energise.

In normal use this would be the "NO FAULT" condition. (Unless this amp uses the opposite convention)

Remove the relay and identify the relay contacts. There will be two COMMON pins, two NORMALLY OPEN and two NORMALLY CLOSED. Unless the contacts are burnt out it will be easy to identify the C and NC.

As the relay has been commanded to OPERATE, there is no problem in shorting each COMMON to the NORMALLY OPEN pin on the PCB.

Do note though that the relay may be there to prevent turn ON - "THUMP", as well as to prevent speaker damage.

You might get a "THUMP" as you turn the amplifier ON.

Better solution would be to fit another relay on the jumper wires if the pin layout is different from the original.

The relay should be easy enough to substitute.

If you keep the jumper wires to about 3cm the replacement relay will sit quite nicely above the PCB and will not affect its performance.

Last edited by KatieandDad; 12th January 2012 at 04:15 PM.
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Old 13th January 2012, 04:44 AM   #3
Mote is offline Mote  Estonia
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Thanks for information.
I am definetly going to replace the relay. I wanted to install the jumpers just to troubleshoot the amplifier further because right now there is no telling whether the amp will produce audio or not.
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Old 15th January 2012, 09:38 PM   #4
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Replaced relay, amp works fine now.
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