troubleshoot - CA amp

[Jith77]

got an old ca 540a (v1 secondhand) and am using it for the first time....but after playing a couple of hours it switches off and doesnt turn back on....i did try to feel the surface but didnt find it hot....after playing around with the cables and a day...it turned back on and then after a couple of hrs went off again....plus the protection LED does not work...so cant figure out what...

am new to all the amp buisness..so someone please come forward with some ideas

 

[flanker.r]

what is the DC resistance of the speakers? try measuring it with a multi-meter

are there any strands of speaker wire of one channel touching the other or the body of the amp

 

[marsilians]

sounds like it could be going into protection mode or there is a loose component/connection inside that is causing the fault. But this is only the symptom of the fault and not the fault itself.

Is the issue repeatable with same song at a point? Check the speaker wires if they are shorting it somehow?

What happens if you just leave it on without anything connected to it? Does it switch off?

 

[Jith77]

my bad...sorry...the amp was not switching off...it doesnt play the speakers

it does play via the headphone out....and when i remove the headphone from the phone socket, it plays the speakers for a sec...then again it doesnt give any output via the speakers... it still plays through headphone out

there is a small click sound from the amp when it shuts the speaker output

speakers used are MS 902i

i tried switching from connection for speaker "A" to speaker "B"...same issues..

what is the DC resistance of the speakers? try measuring it with a multi-meter

are there any strands of speaker wire of one channel touching the other or the body of the amp

i use bare wire...so had checked the wires a couple of times...it is not touching the amp body or the other connections

the Dc resistance thingy is a bit unknown to me...am i supposed measure across the amp output binds/ speaker binds with connection to amp?

sounds like it could be going into protection mode or there is a loose component/connection inside that is causing the fault. But this is only the symptom of the fault and not the fault itself.

Is the issue repeatable with same song at a point? Check the speaker wires if they are shorting it somehow?

What happens if you just leave it on without anything connected to it? Does it switch off?

it wasnt with the same song

speakers wires were checked...

and the amp doesnt switch off ..it is running fine..but doesnt give output to speaker

 

[flanker.r]

select the min resistance setting on multimeter (usually 200 ohms). connect the probes to the speaker posts(+ to red and - to black. it wont matter even if u connect it the other way too). the amp should not be connected. now measure the reading and let us know

 

[Jith77]

K. . . Will have to buy a multimeter first. . . .wats the approx cost and does brand matter?

 

[flanker.r]

buy a basic multi-meter for about Rs 200-250.

 

[Jith77]

Taut

Speaker protection activating, this can be due to anything. The click is the relay activating.

Try to eliminate the speakers - run the amp at a very low volume (till you can barely hear it) and measure the time it takes before the protection is kicking in. Now turn it up loud - is it turning off sooner, later, or no difference?

Which speakers are we referring to here, and what cables have you used, what is the source and ICs? Protection can be cased by an oscillating amp, so let's see if we can narrow this down. Do you have an additional pair of speakers (quality is not important) to test with?

It could also be an internal defect, but we'll get there in some time.

protection kicks in almost immediatly at zero volume when removing headphones. . . Though there instances earlier when it happened only on increasin the volume knob a little, i.e before any audible volume. That too didnt consume any measurable time

speakers are mordaunt short 902i. Speaker wire-bandridge 1.5mm thick ofc wire. I/c - mx rca . Source- esi juli@ soundcard.

i dont have any other passive speaker. Now using a computer speaker connected to the soundcard and the soundcard is working fine.

 

[marsilians]

She needs a service engineer if it's kicking in without playing at all. I wouldn't advise self-help.

No we still ain't sure the source of the problem is the amp though it might end up to be.

I suggested some tests including letting it run w/o attaching speakers, lets wait for the results after removing as many variables as possible.

 

[Jith77]

My multimeter is showing a 1 on the left of the screen whether its connect it to nothing/touch the leads with each other/connect to the speaker. Is this normal ya the meter is not workin?
settings are 200 ohm . . Red lead to v ohm ma. . . Black to COM.
Does checkin it with a pencil battery help