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Old 1st September 2012, 07:34 AM   #21
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by redrooster View Post
The collector of Q820 measures 9-12v.its base to emitter measurement is .673v. I should mention the power relays will click in sometimes after about 30 seconds?
The B-E volts suggests Q820 should be fully on.

If Q820 collector is reading anything other than near to zero volts when pin 19 of the uP is at 19 volts then there is a problem.

I suspect there are going to be other issues too but this is one definite problem. Providing there is nothing physically wrong with the PCB and connectivity then Q820 appears faulty. It has to turn on fully given 19 volts on pin 19.

(And just trying to cover all bases on this... without a scope check on pin 19 we are assuming it is DC (it should be) but what if it is not ? That could cause a DVM to give a misleading reading. So another check could be to connect a 10K resistor from the base of Q820 to the 5.6 volt rail to force Q820 into conduction. That should fire the relays instantly.

I would normally use a scope for all the DC measurements on a fault like this as it lets you see other problems such as noise on the rails)
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Old 1st September 2012, 11:52 AM   #22
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Quote:
Originally Posted by Mooly View Post
The B-E volts suggests Q820 should be fully on.

If Q820 collector is reading anything other than near to zero volts when pin 19 of the uP is at 19 volts then there is a problem.

I suspect there are going to be other issues too but this is one definite problem. Providing there is nothing physically wrong with the PCB and connectivity then Q820 appears faulty. It has to turn on fully given 19 volts on pin 19.

(And just trying to cover all bases on this... without a scope check on pin 19 we are assuming it is DC (it should be) but what if it is not ? That could cause a DVM to give a misleading reading. So another check could be to connect a 10K resistor from the base of Q820 to the 5.6 volt rail to force Q820 into conduction. That should fire the relays instantly.

I would normally use a scope for all the DC measurements on a fault like this as it lets you see other problems such as noise on the rails)
Hi Karl,The Q820 measurement B-E was done with a DMM when the unit was off unplugged with no battery's installed and the collector of Q820 measures 8v-12v the voltage keeps changing on it?. Pin 19 on the MCU is actually 4.6v-4.8v.Not 19 volts. Ive been trying to work this amp out for about two months now and I got a bit flustered & frustrated the other day but I'm OK now.
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Old 1st September 2012, 01:06 PM   #23
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Thats my mistake typing 19 volts.

All the above still applies though. With the unit on and pin 19 at 4.8v ish then Q820 must be fully on and its collector should be at near zero volts. In turn that should pull the relays in. If the collector is not at zero and the relays are not pulled in then this becomes a way into the fault/s as its a part of the circuit that should operate in isolation. So we need to confirm this first.

As mentioned, I suspect there will be other issues but this is a way into a definite problem.
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Old 1st September 2012, 08:46 PM   #24
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What I cant work out is where that voltage on Q820 collector is coming from? I replaced Q820 with a new one and it measures OK in and out of circuit.Another thing is, on board P500 diode Q536 someone had added a wire link from the pointy end of the diode ha! I cant remember if its the anode or cathode.To pin5 on Q501 MCU which is the high level AC outlet pin.I measured pin19 with a scope and its OK pure DC.
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Old 2nd September 2012, 07:38 AM   #25
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Q820 connects via the relay coils to the main auxilliary PSU. Thats to C821. Check the voltage there is correct. Its shown as 33 volts in the manual.

(So with Q820 OFF you should read that same voltage on the collector... yet you mention 8 to 12 volts. Something not right around there so have a measure )
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Old 2nd September 2012, 06:06 PM   #26
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Quote:
Originally Posted by Mooly View Post
Q820 connects via the relay coils to the main auxilliary PSU. Thats to C821. Check the voltage there is correct. Its shown as 33 volts in the manual.

(So with Q820 OFF you should read that same voltage on the collector... yet you mention 8 to 12 volts. Something not right around there so have a measure )
C821 measures 24.1v on the + side. C821 is 100uf,on the schematic but is 1uf, on the parts list,I have 1uf installed currently,should I change it over to the 100uf? P.S. Diode Q815 measures 34v on its (cathode,pointy bit end) and 10.2v on Q820 collector.

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Old 2nd September 2012, 06:16 PM   #27
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1uF sounds really low. Its function is a reservoir capacitor and at 1uf I can't see it doing anything.

It is a strange circuit. The diode Q815 and C822 (the 330uf) is the main reservoir cap for that rail and auxilliaries with the diode isolating the relay drive voltage.

What it means is that the time constant for the relay supply can be made low (so the relays drop out instantly on power disconnection, while the 330uf keeps the other rail alive a fraction longer.

1uF sounds way to low and would explain the relays humming (think you mentioned that a while back) due to the excess ripple voltage.

Try a 100uf and see what the effect of that is.
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Old 2nd September 2012, 07:46 PM   #28
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Quote:
Originally Posted by Mooly View Post
1uF sounds really low. Its function is a reservoir capacitor and at 1uf I can't see it doing anything.

It is a strange circuit. The diode Q815 and C822 (the 330uf) is the main reservoir cap for that rail and auxilliaries with the diode isolating the relay drive voltage.

What it means is that the time constant for the relay supply can be made low (so the relays drop out instantly on power disconnection, while the 330uf keeps the other rail alive a fraction longer.

1uF sounds way to low and would explain the relays humming (think you mentioned that a while back) due to the excess ripple voltage.

Try a 100uf and see what the effect of that is.
Yes that makes sense,I cant find any 100uf caps with the right voltage,only 80v,100v,160v,the 80v elna wont fit physically anyway and the 100v is getting a bit too high I think so Ill wait until the shops open in the morning & get one. Its 2.40am here,so I'm off to bed and will let you know how it went Karl.
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Old 3rd September 2012, 06:25 AM   #29
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OK that did the trick! now there's no hum at all and when I plug it in to the mains it smoothly turns on the relays and the green light is on it just takes a bit longer to turn on sometimes. J823 is measuring 12v,J829 is 32.5v? I was hoping against hope that the functions would work as well when I turned it on LOL. Oh no! I just noticed that I'm getting +52v & -53v respectively thru the top of the metal aluminum case on my main filter caps! that cant be good can it?
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Old 3rd September 2012, 07:36 AM   #30
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So that seems like one problem fixed. Those voltages sound correct now with the relay running at approx the correct coil voltage (24 volt relay... 32.5-12).

Its normal to sometimes measure voltage on the outer can of a cap... it all depends on the internal construction.

The other issues could be more difficult to find. If a lot of different functions aren't working then it's usually best to concentrate on just one and try and fault find that. Anything around the uP requires the checking of all the input and output ports as mentioned before.
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