I am working on an Onkyo A10. I have recapped the unit and replaced the dual 13kuf 63v caps (both measured abut 6kuf) with 4 x15kuf 63v caps.
With no load the amp biases fine and draws about 0.5A at idle- so I thought all good- time to test and measure the amp. However when I connect it to my dummy load (Sencore PA81) the current bounces from initial influx to about 0.5A and then takes off again to over 1 amp-at which point I switch off the amp.
So I then tested each amp module (removing the power connections to the main amp board), and on the left channel I attached a speaker- and no problems other than a small turn on click- so then I put my Fluke handheld meter across the speaker and again over 1 amp. When I connected the right amp to a speaker there was a more pronounced click than on the left.
I have attached a photo of the wiring for the caps- in case I have done something dumb(always a possibility). btw there are no inputs to the amp.
Could the amp be oscillating or any thoughts on what could be causing this?
With no load the amp biases fine and draws about 0.5A at idle- so I thought all good- time to test and measure the amp. However when I connect it to my dummy load (Sencore PA81) the current bounces from initial influx to about 0.5A and then takes off again to over 1 amp-at which point I switch off the amp.
So I then tested each amp module (removing the power connections to the main amp board), and on the left channel I attached a speaker- and no problems other than a small turn on click- so then I put my Fluke handheld meter across the speaker and again over 1 amp. When I connected the right amp to a speaker there was a more pronounced click than on the left.
I have attached a photo of the wiring for the caps- in case I have done something dumb(always a possibility). btw there are no inputs to the amp.
Could the amp be oscillating or any thoughts on what could be causing this?
Attachments
Was it working before the 'repair' ??
If so go back over all your work
What precisely are the bias levels on each channel? , that will pinpoint if you have an final amp problem or it's the PSU
And what DC offset is there on each channel ?
(All four measurements with no signal)
PS: This sentence doesn't make any sense:
If so go back over all your work
What precisely are the bias levels on each channel? , that will pinpoint if you have an final amp problem or it's the PSU
And what DC offset is there on each channel ?
(All four measurements with no signal)
PS: This sentence doesn't make any sense:
What do you mean you put your meter across the speaker? in volts mode I take it ? .... and as a result of this the mains current goes up ??
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sorry- yes I had my Fluke connected across the speaker terminals to try and see what DC (if any was there)
I will come back with bias and DC offset measurements
and yes I have been through all my work looking for mistakes, solder joint problems etc, and all looks OK-though I will check again
Thanks
I will come back with bias and DC offset measurements
and yes I have been through all my work looking for mistakes, solder joint problems etc, and all looks OK-though I will check again
Thanks
Further question:
Did you re-cap throughout ? or just these four reservoirs?
and ..... answer the question 😀 - was it working before your 'repair' ??😕
Are you absolutely sure you're probing the right positions?
Come back with your Bias levels and DC offset levels and we'll go from there.
Another check I'd like you to do is confirm with respect to chassis ground is the voltages on the main reservoir caps (the +, - and the centre connection), both pairs.
Did you re-cap throughout ? or just these four reservoirs?
and ..... answer the question 😀 - was it working before your 'repair' ??😕
That's ridiculous , a multimeter with a ~10Mohm input , set for DC volts, with the leads in the correct holes ?., connected across the sspeake final output ?.. takes the mains current up by 0.5A ??
Are you absolutely sure you're probing the right positions?
Come back with your Bias levels and DC offset levels and we'll go from there.
Another check I'd like you to do is confirm with respect to chassis ground is the voltages on the main reservoir caps (the +, - and the centre connection), both pairs.
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OP has to decide volts or amperes and connect and read his DMM the correct way.
It also helps to use a clear language (compared to the wiring mess).
It also helps to use a clear language (compared to the wiring mess).
so I Have recapped the complete unit- something I do a lot of- though that does not mean I have not made a mistake..🙂
and did I test the amp before working on it?- well no- so mea cupla- i was told there was a problem on the right channel and the amp had been storage for a long time.
and yes the it is ridiculous- but it happens
So the bias initially at 30mv rising to 40mv as the amp warms up- manual specifies 40mv +/- 10
The DC on the left initially is 230mv then drops to 16mv, on the right it is over the mv range of the meter- so maybe 0.5v and drops to 25mv.
Interestingly when I put the meter across the right channel and the main PSU caps still had charge- the mains current drain jumped again.
and did I test the amp before working on it?- well no- so mea cupla- i was told there was a problem on the right channel and the amp had been storage for a long time.
and yes the it is ridiculous- but it happens
So the bias initially at 30mv rising to 40mv as the amp warms up- manual specifies 40mv +/- 10
The DC on the left initially is 230mv then drops to 16mv, on the right it is over the mv range of the meter- so maybe 0.5v and drops to 25mv.
Interestingly when I put the meter across the right channel and the main PSU caps still had charge- the mains current drain jumped again.
Big mistake... nay - huge mistake, you have no idea whether you've introduced a problem or it was there before you work (and still there)
I make no apologies in saying you've dug yourself a huge hole and potentially a whole lotta work there by not testtng beforehand for this type of job.
Both channels ??
Steady state is what we're interested in (and that's steady state with a speaker/load connected), on this amp there is no adj pot for DC offset, you have to make and break jumpers to get it into line.
This again sounds like non-sense, what do you mean still had charge ? ithe amp was still turned on at the mains ??
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@as_audio- I am reading the DMM correctly-
@MikePP- yes readings are +/-45v on the main caps for both channels measured from the center and of the caps and the chassis earth
@MikePP- yes readings are +/-45v on the main caps for both channels measured from the center and of the caps and the chassis earth
agreed on lack of prior testing
yes both channels are 40mv
sorry I meant the main PSU caps still had some charge in them
apologies for the lack of clarity
yes both channels are 40mv
sorry I meant the main PSU caps still had some charge in them
apologies for the lack of clarity
Then your meter is knackered
There's no way in hell any AC current (which is what you say you're measuring ) can flow if it's turned off and the main res. caps are slowly discharging across the bleed resistors you've got fitted.
Sorry MikePP-
I will try an be more clear and concise-
I have a sencore PR57 to which the amp is connected. When I turn the amp on and there is some residual voltage in the main PSU caps, and I have a DMM connected across the right channel speaker terminals set to measure DC- the Sencore shows the initial current inrush and then it rises to over 1amp. I then shut down the AC to the amp by switching the PR57 off- The PR57 is set for Current measurement on the 0-1.5Amp
I will try an be more clear and concise-
I have a sencore PR57 to which the amp is connected. When I turn the amp on and there is some residual voltage in the main PSU caps, and I have a DMM connected across the right channel speaker terminals set to measure DC- the Sencore shows the initial current inrush and then it rises to over 1amp. I then shut down the AC to the amp by switching the PR57 off- The PR57 is set for Current measurement on the 0-1.5Amp
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So now we would have to ask - what is sencore PR557 .. may be the dmm.
Do you use two meters, would you care to explain more precise ? Thanks.
Do you use two meters, would you care to explain more precise ? Thanks.
The Sencore is a variac/isolation stransformer with inline meter- one of my most useful tools
http://manuals.repeater-builder.com/te-files/SENCORE/SENCORE PR57 Operation & Service.pdf
I have a number of DMM's - the Handheld I mainly use is a Fluke 79 III and the the desktop I use is a 5.5 digit SIGLENT 3055.
I hope this answers your question
http://manuals.repeater-builder.com/te-files/SENCORE/SENCORE PR57 Operation & Service.pdf
I have a number of DMM's - the Handheld I mainly use is a Fluke 79 III and the the desktop I use is a 5.5 digit SIGLENT 3055.
I hope this answers your question
So you're saying if you leave the amp turned off for quite some time (so the res caps are fully discharged via those bleed resistors I see) , the amp powers up and draws ~0.5A
Then if you connect a DC volts multimeter across (either?) channel output , the current jumps up to ~1A ??
Then if you remove meter and turn amp off and on again (within a short time - not enough for the res caps to discharge ) and then turn back on the current goes to ~1A
You have be absolutely precise when explaining what you've done, because a lot of the posts so far you've left a lot of crucial detail out. (read it out to yourself before posting)
If putting a multimeter across the speaker output makes the AC current double from 0.5 to 1A then the meter must be faulty, I repeat there's no way a meter with ~10Mohm input impedance can do this - it's just not possible - unless it's faulty. (Set to the wrong range - possibly, but not on V setting)
The bias (from what you say) looks normal, the DC offset also looks within spec.
@mikePP
I will undertake the process exactly as you describe- with no load on the output and report back.
I am wondering is it is the protection circuit?
and I am very sure the meters all function as they should- but will test them all
thanks for the help- as you say this should not happen
I will undertake the process exactly as you describe- with no load on the output and report back.
I am wondering is it is the protection circuit?
and I am very sure the meters all function as they should- but will test them all
thanks for the help- as you say this should not happen
The Fluke meter I am using works on Voltages, Ohms, diodes and capacitance- so I am comfortable it works.- Also used the siglent DMM and had the same results.
The PR57 meter works exactly as I expect- I fully believe the meter is accurate- I measured the current with the siglent and it is the same as reported by the PR57.
From a cold start - no load no meter across the speaker terminals, the amp quickly stabilizes at 0.5A-
On the first "warm" start- and with the meter connected set on Volts range-there is still voltage in the PSU caps- after the initial inrush, the meter drops to around 0.5A and then shoots to around 1A- then I turn off the amp
On a second "cold" start (power supply caps have about 2-3v in each), and with the meter connected- the amp quickly settles at 0.5A.
On a second "warm" start- with the meter connected- after the inrush the meter drops to 0.5A and then shoots to around 1A. (the PSU caps all had around 13-15v by the time I got a probe onto them)
Given the meter is providing a very high resistance from the output to ground and this occurs with some voltage still in the power supply circuit, I think there are two possibilities
1) there is an earth connection that is faulty
2) the current detector (Q17) and/or the protection circuit has an issue
1)-I will check all the point to point earth wiring (I have done this, but will be more methodical)
2)- I will remove and check all the transistors in the current detector and protection circuit and then the resistors- the caps have been replaced- I will check these as well. There is also a new relay.
All the output transistors have been checked (Peak DCA75) and all test good (one has an Hfe of 100 vs all others are around 150)
I will report back, though this will take a little time
The PR57 meter works exactly as I expect- I fully believe the meter is accurate- I measured the current with the siglent and it is the same as reported by the PR57.
From a cold start - no load no meter across the speaker terminals, the amp quickly stabilizes at 0.5A-
On the first "warm" start- and with the meter connected set on Volts range-there is still voltage in the PSU caps- after the initial inrush, the meter drops to around 0.5A and then shoots to around 1A- then I turn off the amp
On a second "cold" start (power supply caps have about 2-3v in each), and with the meter connected- the amp quickly settles at 0.5A.
On a second "warm" start- with the meter connected- after the inrush the meter drops to 0.5A and then shoots to around 1A. (the PSU caps all had around 13-15v by the time I got a probe onto them)
Given the meter is providing a very high resistance from the output to ground and this occurs with some voltage still in the power supply circuit, I think there are two possibilities
1) there is an earth connection that is faulty
2) the current detector (Q17) and/or the protection circuit has an issue
1)-I will check all the point to point earth wiring (I have done this, but will be more methodical)
2)- I will remove and check all the transistors in the current detector and protection circuit and then the resistors- the caps have been replaced- I will check these as well. There is also a new relay.
All the output transistors have been checked (Peak DCA75) and all test good (one has an Hfe of 100 vs all others are around 150)
I will report back, though this will take a little time