I've got a Kenwood KA-5002 amp that is all original except I replaced the trimpots on the driver board with multi-turn trimpots as that permits the adjustments to be made more accurately.
Ever since I've had the amp the null balance switch and one coil wire on the relay has been disconnected.
When I touch the wire to the relay coil terminal the relay actuates.
What could be the problem there, what is the purpose of the null balance switch and should it be momentary push or latching?
Also do I need to recap the amp or is it ok as is?
Checked the DC offset voltages and they are -45mV and -27mV so there's no legitimate amp stage fault causing the protection circuit to kick on.
Here's something interesting.
My unit's serial number is 411160 and should be the 240001 schematic, but mine has the four diode one transistor circuit that the serial numbers from 430001 have and mine looks to have the 240001 speaker protection circuit, but it all looks factory wired except where someone disconnected wires and soldered them back to maybe troubleshoot it before I bought the amp.
So I'm not sure how to even begin troubleshooting given no schematic I have exactly matches the official schematic or maybe that was an undocumented mod perhaps?
Sure the amp works fine without the speaker protection and has ran like that several years off and on, however I know why the speaker protection is there and that it is necessary to have it.
So looking at the protection circuit I wonder if QY5 or QY6 is bad as all terminals of the two adjustment pots have +52V on them as they should so that means QY1-4 is not turned on and the relay should not be on.
Ever since I've had the amp the null balance switch and one coil wire on the relay has been disconnected.
When I touch the wire to the relay coil terminal the relay actuates.
What could be the problem there, what is the purpose of the null balance switch and should it be momentary push or latching?
Also do I need to recap the amp or is it ok as is?
Checked the DC offset voltages and they are -45mV and -27mV so there's no legitimate amp stage fault causing the protection circuit to kick on.
Here's something interesting.
My unit's serial number is 411160 and should be the 240001 schematic, but mine has the four diode one transistor circuit that the serial numbers from 430001 have and mine looks to have the 240001 speaker protection circuit, but it all looks factory wired except where someone disconnected wires and soldered them back to maybe troubleshoot it before I bought the amp.
So I'm not sure how to even begin troubleshooting given no schematic I have exactly matches the official schematic or maybe that was an undocumented mod perhaps?
Sure the amp works fine without the speaker protection and has ran like that several years off and on, however I know why the speaker protection is there and that it is necessary to have it.
So looking at the protection circuit I wonder if QY5 or QY6 is bad as all terminals of the two adjustment pots have +52V on them as they should so that means QY1-4 is not turned on and the relay should not be on.
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Problem solved. Q5 was bad. Showed a resistance of 135 ohms between base and collector out of circuit.
There anything I need to watch out for with this amp or is it good to go now?
I eventually will recap the amp when I get one of these
There anything I need to watch out for with this amp or is it good to go now?
I eventually will recap the amp when I get one of these