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Old 25th September 2014, 01:06 AM   #1
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Default mx 3040

This Sony amp protect and power LED is on.When i power the amp the relay engage and disengage very quickly.Amp has rail voltage .I get good audio on the relay.I think the protection circuit has a fault.Any idea what to check?
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Old 25th September 2014, 01:22 AM   #2
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Location: Louisiana
XM-3040F?
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Old 25th September 2014, 01:26 AM   #3
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I thinks so,amp is old so maybe the F fade out.
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Old 25th September 2014, 01:33 AM   #4
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I just saw a pic of the F version and mine is different.The relays are mounted on a small board soldered to the main board. I will post pic tomorrow but mine look just like this but with black relays.

Not my pic""
http://i598.photobucket.com/albums/t...0/DSC02473.jpg
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Old 25th September 2014, 03:17 AM   #5
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Location: Louisiana
Post the DC voltage on all pins of IC505.
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Old 26th September 2014, 12:49 AM   #6
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IC505
1: 0.948
2: 0.275
3: 0.651
4: 1.879
5: -0.104
6: 11.60
7: -0.056
8: 3.148

The voltage was stable only for pin 6 and 8. The rest was going a little up and down.
Base on the date sheet for that IC pin 8 Vcc should be higher than that.I pull the IC and
got 15.65v on the Pad pin 8.I put the IC back in and soldered pin 8 and 5 .I check voltage again
and it went back to 3.148.
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Old 26th September 2014, 06:40 AM   #7
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Location: Louisiana
The voltage on pin 8 is probably OK. Pin 1 is above the threshold for that input. That's the over-current detect input. Pulling Q505 should defeat that part of the protection circuit and allow you to determine if there is a true over-current fault or a fault in the protection circuit. The Qx06 transistors are the over-current detection transistors for the individual channels.
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Old 27th September 2014, 01:43 AM   #8
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I pull each over-current transistor one by one but no change.I pull Q505 amp is out of protect ,but after about 1 min comes back in protect.when amp was out of protect i get good audio on all channel.
Q505 in circuit
E: 22.56
C: 22.62
B: 21.98

out if circuit pads read
E: 25.60
C: 3.04
B: 23.92

With Q505 out i get 1.096 on pin 1 of IC505.With all parts in circuit if i GND pin six or seven amp comes out of protect
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Old 27th September 2014, 02:08 AM   #9
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Join Date: Nov 2003
Location: Louisiana
If IC505 has voltage on pin 1, the problem may be the thermistor or the connections to the thermistor. Try grounding pin 1 of IC505 to see if that prevents it from going into protect mode but be careful in case there is a real fault.

Grounding pin 7 shouldn't (as far as I can tell) prevent the amp from going into protect mode.

Grounding pin 6 simply switches on the relay drive transistor which engages the relays.

email me if you want the diagram.
babin_perry@yahoo.com
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Old 27th September 2014, 02:52 AM   #10
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When i ground the pins i hear the relay engage so i assume it was out of protect in that state.
I will check the thermistor tomorrow.
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