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EQ573 Equaliser / Re: EQ573-II doesn't play sound

« Last post by JPK on February 22, 2026, 10:09:45 AM »

Check if you get the signal on U1 pin 5.
- If not, the issue is around the high pass filter. Check the solder joints on rotary switch SW1, connectors J5a-b and J6a-b.
- If true, the issue is in the relay RLY1 or in U2. Check the solder joints. Try replacing.

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EQ573 Equaliser / Re: EQ573-II doesn't play sound

« Last post by andrixb on February 21, 2026, 01:43:23 PM »

Checked. On TP3 is 0.9VAC and TP4 0.8VAC

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EQ573 Equaliser / Re: EQ573-II doesn't play sound

« Last post by JPK on February 20, 2026, 11:36:28 AM »

Also check TP3 and TP4 (the audio goes through them before TP2).

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EQ573 Equaliser / Re: EQ573-II doesn't play sound

« Last post by andrixb on February 19, 2026, 01:02:07 PM »

Thanks. 
I can get 1VAC on TP1, but now it is 0VAC on TP2. Soldier joints look fine. Could it be an issue with the U2 THAT1646?

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EQ573 Equaliser / Re: EQ573-II doesn't play sound

« Last post by JPK on February 18, 2026, 04:48:29 PM »

Check the value and solder joints of R1...R4, C4, C5, U1, RLY1.
Check the direction of U1, RLY1.
Try swapping U1 with one that you are sure of.

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EQ573 Equaliser / Re: EQ573-II doesn't play sound

« Last post by andrixb on February 18, 2026, 11:45:53 AM »

Hi

Thanks for the suggestion.

I get a sound in bypass if it is connected to the MP573; nothing gets through otherwise.
On TP1, I get 0VAC. The board is REV2.3B, and the C8 is oriented as in the picture (negative facing the back of the launchbox)

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AB528 Microphone preamplifier / Re: AB528 DI not working

« Last post by JPK on February 17, 2026, 10:18:48 AM »

Not good! Pins 1, 2, 3, 6 shoulb be at 0V.
Check the solder joints on J4a-J4b.
Look for a solder bridge on U2, on the jack or on the connectors J4a-J4b.


Maybe one of them is no good?
You can check them in circuit with your DMM in diode test mode.

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AB528 Microphone preamplifier / Re: AB528 DI not working

« Last post by Ritualknive on February 16, 2026, 09:37:01 PM »

They are in correctly. Maybe one of them is no good? Also I’m also now noticing when using the mic/line in the 1200 ohm position there is a constant tapping or ticking type of sound. Only on the 1200 setting. 

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EQ573 Equaliser / Re: EQ573-II doesn't play sound

« Last post by JPK on February 16, 2026, 05:32:44 PM »

Do you get a sound in bypass?
You must try to follow the signal on TP1, TP3, TP4, TP2, as described here.
It will tell you where the signal stops.

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AB528 Microphone preamplifier / Re: AB528 DI not working

« Last post by JPK on February 16, 2026, 05:22:32 PM »

Check that diodes D12 and D13 are installed in the correct orientation: The "k" on the PCB is the ring on the diode.