KAM KXR1000 amp - one channel in protect mode

[oddbodd]

I've volunteered to have a look at this amp, which belongs to my local club.

I've brought it home and opened it up. After blowing out loads of dust, there doesn't seem to be anything obviously wrong. No bloated caps etc.

Channel A is in protect mode. Channel B worked fine at the club. No change, with no speakers or anything plugged in.

Any pointers?

[budm]

Re: KAM KXR1000 amp - one channel in protect mode

Any good clear pictures so we know what we are dealing with?

[oddbodd]

Re: KAM KXR1000 amp - one channel in protect mode

Here's some I took yesterday. Not brilliant pics, I'm afraid.

[Andrew F. Ali]

Re: KAM KXR1000 amp - one channel in protect mode

Since channel B is working. Compare voltages at the similar points of each channel. Connect a load (speaker) on each channel before turning on the power. I suggest on transistor Collectors and Vcc IC pins. More than likely the problem may be in the Output Stage (ICs or Transistors Shorting)

[oddbodd]

Re: KAM KXR1000 amp - one channel in protect mode

OK, thanks.

I've now tested the transistors, and found one at T323, which is suspect.

The readings are:
- to base and + to emitter = 1732
- to base and + to collector = 1
+ to base and - to emitter = 704
+ to base and - to collector = 558

Going by the readings on the other transistors, the - to base and + to emitter reading should be 1, not 1732.

Does that sound right?

[Andrew F. Ali]

Re: KAM KXR1000 amp - one channel in protect mode

Personally, I prefer to use an analog VOM to test transistors. I would set the VOM on the Rx1K or Rx1000 scale and do my testing.
First I would remove the transistor out of the cicuit board. If I am to do a quick check I would set my VOM on the Rx1 scale and do an in-circuit check.
However, removing the transistor under test completely out of the circuit board is best.

[budm]

Re: KAM KXR1000 amp - one channel in protect mode

It is 2SD2083 NPN transistor. Checking part when still on the board is not reliable, since it has two channel, you can do comparison readings of the same transistor to see what you get. Each channel has that speaker protection relay (blue rectangular box), listen to see if the dead channel click on or not.
Did you try contacting them to see if they are willing to send you the diagram/service manual?
http://www.kam.co.uk/index.php?actio...product_id=103

[oddbodd]

Re: KAM KXR1000 amp - one channel in protect mode

Thanks guys.

I did compare the readings with the others, and this is the only one that's suspect.

I'll check that relay, to see if it's switching. I'm also inclined to remove that transistor and test it off board anyway.

Edit: I've also requested a schematic/service manual.

[ben7]

Re: KAM KXR1000 amp - one channel in protect mode

Thanks guys.

I did compare the readings with the others, and this is the only one that's suspect.

I'll check that relay, to see if it's switching. I'm also inclined to remove that transistor and test it off board anyway.

Edit: I've also requested a schematic/service manual.

With amplifiers, if one transistor is bad, usually more are bad. You should test all the others on that same channel, even the ones not on the heatsink.

Otherwise, looks like a decent amp!

[oddbodd]

Re: KAM KXR1000 amp - one channel in protect mode

The speaker protection relay that budm mentioned, is not switching.

[Andrew F. Ali]

Re: KAM KXR1000 amp - one channel in protect mode

OK. So the 2SD NPN output transistor is suspect.
Then the complemetary 2SA or 2SB PNP output transistor may also have failed.
This pair of output transistors would be configured in PUSH-PULL.
They are actually Darlington transistors and would test slightly different from a 'normal' transistor.
Test the big white resistors also, they may have increased in value or burnt out too. They might be 0.22 Ohms 3 Watt resistors.
Yes remove the suspect components from the circuit to test them accurately.
Also, test the smaller Driver transistors in the circuit as advised, as they too might have suffered some stress.
Remove them from the circuit board for testing and observe their pin positions for re-installing. See if there are any EBC markings on the board's underside and a position drawing on the upperside, to guide you.
Test the power Fuses as they should have burnt open to protect the system.
Always replace fuses with the same rating.

[budm]

Re: KAM KXR1000 amp - one channel in protect mode

It probably sensing high DC offset voltage at the output so it stays in protection mode. The circuit is direct couple so testing component in the board will not be reliable, they need to be remove. Darlington has such high current gain, it will not take much leakage current in the bad transistor to cause problem.

[oddbodd]

Re: KAM KXR1000 amp - one channel in protect mode

Thanks for that. Lots to check, now.

Fuses appear to be OK.

[kc8adu]

Re: KAM KXR1000 amp - one channel in protect mode

or in any stage from the input forward.
i would fire it up and measure from ground to the base of each output transistor.the bad one or the one driven by a bad stage will stand out.

It probably sensing high DC offset voltage at the output so it stays in protection mode. The circuit is direct couple so testing component in the board will not be reliable, they need to be remove. Darlington has such high current gain, it will not take much leakage current in the bad transistor to cause problem.

[oddbodd]

Re: KAM KXR1000 amp - one channel in protect mode

Schematic for info.

[oddbodd]

Re: KAM KXR1000 amp - one channel in protect mode

Has anyone got a service manual for this amp, please?

[Poloperson]

Re: KAM KXR1000 amp - one channel in protect mode

Hi, Did you get anywhere looking for a service manual for the amp? I have the same one and I too have some problems I need to look at, so a manual would be really useful.

[oddbodd]

Re: KAM KXR1000 amp - one channel in protect mode

Unfortunately not.