C312 is a smoothing capacitor for the overcurrent detector. It could well be the cause of your problem.
The first thing to do is to fix that solder joint as a temporary measure to see if the problem is fixed or changed. (Power off the amp first!)
As @sgrosklass points out it's probably a bad part and you should replace it. Just observe the markings on the part and install the new one the same way. Yes it is polarized the stripe on the casing is negative.
This kind of thing happens as equipment ages... capacitors can leak, solder points break, stuff comes loose... At this point, I think it's probably a good idea to do a full visual inspection of the circuit boards, with a 5 or 10 power magnifying lens and to reflow any solder point that looks even slightly suspicious.
Lets see what's going on after that...
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Very good. Let me know if this fixes it. If not, we can continue with the troubleshooting...
In the mean time you can do the visual and reflow inspection I suggested.
Very unusual to say the least. Is it attached or was it just sitting there?
If it was soldered to the board, on a ground point, it might be a grounding contact for the bottom plate.... but that should have been accomplished through the rest of the chassis.
If it was loose... it's a good thing you found it before disaster struck.
So, like a battery terminal? Got a picture?
This may have been used for making contact to the shield as suggested.
The spring was not attached on the board and show no mark of weld or attachment.
It presents a very weak compression strength (spring diam. 5,5mm with 6 turns of wire diameter 0,25 mm).
Either it comes from a mechanical element of the amplifier, either it comes by mistake from manufacturing ?
I shall contact you again when the new capacitor will be welded.
Thanks again
It presents a very weak compression strength (spring diam. 5,5mm with 6 turns of wire diameter 0,25 mm).
Either it comes from a mechanical element of the amplifier, either it comes by mistake from manufacturing ?
I shall contact you again when the new capacitor will be welded.
Thanks again
Do all the push buttons move correctly when you press them?
That's about the only place I can see a spring being used.
My guess is that it's a stray part, perhaps from the factory. I'd say just hang on to it until you discover where it's needed...
No problem...
All the push buttons move correctly. The spring should be a stray part.
I had to drill again the board where the capacitor C312 had leaked along one of the legs. The hole was plugged. I have received the capacitor but I wait for Isopropylic alcohol.
All others welding points seem to be correct.
What can be done from outside on potentiometers ?
I had to drill again the board where the capacitor C312 had leaked along one of the legs. The hole was plugged. I have received the capacitor but I wait for Isopropylic alcohol.
All others welding points seem to be correct.
What can be done from outside on potentiometers ?
Seems so.
Okay, sounds good.
If you have or can get a spray can of contact cleaner you can spray into each pot and switch, then operate them several times while the cleaner dries.
Beyond that, we're waiting until the new capacitor is installed before there's much to do...
Hi,
I have changed the capacitor C312.
It seems that the system works better but obviously this element was certainly not the only origin of the issue : the relay locks sometimes in protection mode.
I have made a new observation : if I turn slowly the volume button, when the index reaches 2,5/3 the relay cut systematically the output currents.
Thanks for your help
I have changed the capacitor C312.
It seems that the system works better but obviously this element was certainly not the only origin of the issue : the relay locks sometimes in protection mode.
I have made a new observation : if I turn slowly the volume button, when the index reaches 2,5/3 the relay cut systematically the output currents.
Thanks for your help
Okay so it's still going into protection, once again we need to figure out why.
First double check your work, make sure you have good connections and continuity on the circuit board where you changed the part. It is part of the protection circuit, so lets be extra sure.
So turning the volume up causes protection ... is this with music playing, or when silent?
As I explained before there are only 3 things that will cause that relay to drop out putting the amp into protection mode... DC Offset, Overcurrent or AC Loss... we need to figure out which it is.
So with the amp int protection mode...
Measure the voltage at R425 ... both sides.
Measure the voltage at the cathode of D407.
Measure the cathode of D406
Measure the voltage at the anode of D409 .
Measure R423 both sides
Measure R422 both sides
Measure R426 both sides
These measurements are all DC scale to ground.
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Thank you for the readings.
Unfortunately they all indicate a healthy amplifier which didn't help very much.
I need you to get it to go into protection... with the relay open, no output from the speakers... then take the readings again... preferably with no music playing (if it will hold the condition).
You say that turning the balance control all the way left (left speaker only) triggers it... then do that... and take the readings again.
Here are the functions for each of the readings...
R425 : < 1.3 volts == protection.
D407 cathode : < V+ - .5v == right channel overcurrent
D406 cathode : < V+ - .5v == left channel overcurrent
D408 anode : > +.5v == ac loss
R423 : < -0.5v or > +0.6v == Right channel DC offset
R422 : < -0.5v or > +0.6v == Left channel DC offset
R424 : > 15v == relay not pulled in.
From your descriptions so far, it appears there may be a problem in the left channel that is intermittently triggering protection. If my hunch is right and in keeping with the previous suggestion we had it is almost certainly a fault in the left channel and it could be as simple as re-adjusting the amplifier's DC balance and BIAS settings...
I see the service manual gives the procedures for adjusting both and I'm going to suggest you follow them very carefully for both channels. Like so...
Before you start ... turn the amplifier off and unplug it from the wall. Disconnect all inputs and speakers. Wait a little while for everything to discharge and cool to room temperature.
First we clean the contacts ... One at a time drip a couple of drops of your alcohol onto each of the adjustment pots on the top of the circuit board. Using a small plastic screwdriver gently turn them back and forth across their full span several times while wet and put them back in their original positions as closely as you can.
Now once they are all cleaned... follow the procedures in the manual... The amplifier needs to be on, but silent... just sitting there with no inputs and no speakers.
Note that the bias setting is done by reading across a resistor... not to ground.
The DC balance is done from the speaker connectors... so the amp cannot be in protection when you adjust this. Note that if you stray too far, you may trigger protection with this adjustment. In that case turn the pot just a little bit away from where it tripped and it should pull the relay back in so you can get your readings again.
Please note ... these can be very sensitive adjustments. Small moves can make a huge difference, so be patient and gentle with it,
Once you have these settings completed, try all the things that trigger protection again ... and see how it goes.
Unfortunately they all indicate a healthy amplifier which didn't help very much.
I need you to get it to go into protection... with the relay open, no output from the speakers... then take the readings again... preferably with no music playing (if it will hold the condition).
You say that turning the balance control all the way left (left speaker only) triggers it... then do that... and take the readings again.
Here are the functions for each of the readings...
R425 : < 1.3 volts == protection.
D407 cathode : < V+ - .5v == right channel overcurrent
D406 cathode : < V+ - .5v == left channel overcurrent
D408 anode : > +.5v == ac loss
R423 : < -0.5v or > +0.6v == Right channel DC offset
R422 : < -0.5v or > +0.6v == Left channel DC offset
R424 : > 15v == relay not pulled in.
From your descriptions so far, it appears there may be a problem in the left channel that is intermittently triggering protection. If my hunch is right and in keeping with the previous suggestion we had it is almost certainly a fault in the left channel and it could be as simple as re-adjusting the amplifier's DC balance and BIAS settings...
I see the service manual gives the procedures for adjusting both and I'm going to suggest you follow them very carefully for both channels. Like so...
Before you start ... turn the amplifier off and unplug it from the wall. Disconnect all inputs and speakers. Wait a little while for everything to discharge and cool to room temperature.
First we clean the contacts ... One at a time drip a couple of drops of your alcohol onto each of the adjustment pots on the top of the circuit board. Using a small plastic screwdriver gently turn them back and forth across their full span several times while wet and put them back in their original positions as closely as you can.
Now once they are all cleaned... follow the procedures in the manual... The amplifier needs to be on, but silent... just sitting there with no inputs and no speakers.
Note that the bias setting is done by reading across a resistor... not to ground.
The DC balance is done from the speaker connectors... so the amp cannot be in protection when you adjust this. Note that if you stray too far, you may trigger protection with this adjustment. In that case turn the pot just a little bit away from where it tripped and it should pull the relay back in so you can get your readings again.
Please note ... these can be very sensitive adjustments. Small moves can make a huge difference, so be patient and gentle with it,
Once you have these settings completed, try all the things that trigger protection again ... and see how it goes.
Hi,
First I thank you for your patience.
I have carried out Bias and Balance adjustements.
Concerning Bias setting, with RV302 and RV352 in mechanical stop, I get a minimal voltage of 27/28 mV on both channels. Impossible to obtain 15 mV.
Concerning Balance setting I can get voltage values on both sides of 0 V. I suppose that adjustement near 0 V is difficult but possible.
Can you tell me if Bias adjustement modify Balance and vice versa ?
The new positions of RV302 and RV352 are so different from initial tuning that I don't dare to switch on the amplifier...
First I thank you for your patience.
I have carried out Bias and Balance adjustements.
Concerning Bias setting, with RV302 and RV352 in mechanical stop, I get a minimal voltage of 27/28 mV on both channels. Impossible to obtain 15 mV.
Concerning Balance setting I can get voltage values on both sides of 0 V. I suppose that adjustement near 0 V is difficult but possible.
Can you tell me if Bias adjustement modify Balance and vice versa ?
The new positions of RV302 and RV352 are so different from initial tuning that I don't dare to switch on the amplifier...
Put them back where they were in the beginning...
Yes it is likely that one setting will affect the other. You may have to go back and forth several times to get them settled in. Let the amp warm up for a few minutes, just sitting there and try it again...
For the DC balance, you will never get exactly 0... just get as close to 0 as you can. What readings were you getting?
General design practice should have those adjustments landing someplace near the center of their rotation... hitting the end is a potential problem.
Busy week coming up
I should let you know that I have a rather busy week coming up starting Monday. It may take me some time to get to your posts so, rather than having you wait... perhaps some of the others could chime in to help you...
I should let you know that I have a rather busy week coming up starting Monday. It may take me some time to get to your posts so, rather than having you wait... perhaps some of the others could chime in to help you...
No problem, I understand.
Since I have cleaned the variable resistors and adjust Bias and Balance, the amplifier work better.
If I position the Bias variable resistors near the middle of their range I will get a Bias voltage around 35/37 mV (actually, to get closer the target 15 mV, I have positioned the cursor near end range and obtained 29 mV).
Tell me if it is essential that I adjust these variable resistors in mid range regardless of the obtained voltage.
Thank you
Since I have cleaned the variable resistors and adjust Bias and Balance, the amplifier work better.
If I position the Bias variable resistors near the middle of their range I will get a Bias voltage around 35/37 mV (actually, to get closer the target 15 mV, I have positioned the cursor near end range and obtained 29 mV).
Tell me if it is essential that I adjust these variable resistors in mid range regardless of the obtained voltage.
Thank you
The whole centre range thing is an ideal. Nothing ever lands there exactly. The idea when designing is to have some adjustment either way.
I'm glad it's working better. But you might want to check the solder and board for those parts just to be careful.
Hopefully one of the others can help you with the rest.
I'll check when I can.
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