ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Someone with better expertise on the Beomaster 4400 than me will have to confirm but it appears like you need to adjust the DC offset down on your outputs if they are sitting at 1.4VDC. I would expect that voltage to be down in the millivolt range close to 0 VDC. However, as I said, I haven't worked on that receiver. That is 1.4 VDC from those nodes to ground, right?
-sonavor
sonavor:That is 1.4 VDC from those nodes to ground, right?
Yes, but if I adjust the idle current down, I will get away from the 11 mV I adjusted in the first try, I'm checking the RL1 contact, seames to be irratic, cleaning and will try again
Collecting Vintage B&O is not a hobby, its a lifestyle.
Cleaned RL1, no change, turned down R177/277 no change.
I don't see an adjustment for DC offset on the Beomaster 4400 so it must be handled differently (and not something you adjust). The service manual you have is showing the cold, no-load idle current adjustment so you had set that correctly. I'm not sure about your 1.4V then. So between 50 VAC and 80 VAC to the receiver you have 0VDC at the output, but above 80VAC the protection relay engages. Until someone with more expertise answers I would measure key nodes in the protection circuit to see what changes when you go from below 80V to past 80V.
checking at the base of TR16 I get from 0VAC to 80VAC, 0 to 4.5VDC, and stays at 4.5VDC up to 120VAC, Base at IC 3 goes from 0 to 13.7VDCV up to 120VAC
The emitter of IC3 is +15VDC? What does the collector side do?
In doing a rough circuit simulation it looks like you should see +15 VDC on the IC3 emitter, +13.8 VDC on the base and +14.2 VDC on the collector under normal (good) operation. If DC current comes in through the right or left channels (through R46 or R47), it will drive up the IC3 base voltage turning IC3 off and dropping the collector voltage that is controlling the protection relay. So if you are seeing around +14 VDC at the node of IC3 collector, R39, R38 and D22, then the relay should not be in the protection mode. You said that you are seeing +13.7 VDC at the IC3 base so the IC3 collector should be close to +14 VDC. If it is, and the relay is in protection mode then there is something wrong. Or, if the collector is not close to +14 VDC there is something wrong.
I realize that I didn't include the relay in my simulation so I believe that would change what voltage you actually would see at the IC3 collector.
Sorry John, I was havjng my Dice evening with a couple of friends, will look into the IC3 and relay tomorrow, What I dont understand is the 1.4V at R46/47 and then the 4.5V at base of TR16
The 1.4VDC is not at the node between R46 and R47, right? The 1.4VDC you are measuring is the same node as P11 and P12 (leaving the board)?Tomorrow check what the IC3 collector voltage does. Also take voltage measurements across R45, R46 and R47.
One more thing - Is RL1 normally open and power on engages the relay to allow the 35 voltage to the rails?
Are you sure you measured 4.5VDC at the TR16 base and not the node between R45, R46 and R47? You also verified when you have applied full AC power that you don't have positive and negative 35 VDC on the rails, right?
sonavor:The 1.4VDC is not at the node between R46 and R47, right? The 1.4VDC you are measuring is the same node as P11 and P12 (leaving the board)?
Right
Will start now checking. As I see it, the coil on RL1 is activated through IC3, RL1 interrupts the + and - 35VDC.
Going to the workshop
First I'd determine whether the left or the right amp is at fault. Just unplug the +/- 35V connector and see which side triggers the relay. Have you done that?
Jacques
Both channels triggers the RL1
Here measurements at 120VAC
Yes, okay, 1.5V at the output is wrong. But on both channels? What are the odds? A problem at the preamp perhaps? Can you test without the amp input cap(s)? Could it be hum?
Oops
The more I think about it, the more it appears that the voltage doesn't come from the amps at all.
What happens when you disconnect the 680k resistors?
Have you tested TR15/16 out of the circuit?
This is a real thriller.
http://tinyurl.com/qj9cjsf
Interesting, and cool. Those measurements are very close to what I get in the circuit simulator. However, when I try to simulate putting 1.5 VDC at the points you have, it doesn't affect the relay control signal. I have a question about that though. When you are making those measurements, the relay is not engaged (that is the problem) so you don't have plus and minus 35 VDC on the rails. So the 1.5 VDC is coming from fault switch circuit, right? Without +-35 V on the amplifier circuits, they won't be supplying any voltage to the fault switch when you are making your measurement.
Like Jacques, unplug the amplifier voltages and take them out of the equation.
If I disconnect the the R46/47 I may loose fault switch protection, I'm afraid of doing that.
Here the left channel at 75 VAC, just before RL1 is triggered
will desolder TR15/16 and check
TR15/16, B-C, B-E both 0.698V, E-C 0.0, C-B E-B 0.0
sonavor:Like Jacques, unplug the amplifier voltages and take them out of the equation.
Will connect the the TR 15/16 again, disconnect P11 and P12 and check again at P11/12 pin 3
At 120VAC, P11/12, pin3 gives 1.5 VDC, but the relay do not pull, at IC3 E I have 14.7 V, at IC3 C I have 0.0
Connected P11/12 again and back to the same, RL1 triggers at 80VAC
Søren Mexico: At 120VAC, P11/12, pin3 gives 1.5 VDC, but the relay do not pull, at IC3 E I have 14.7 V, at IC3 C I have 0.0
I'm not sure I am following correctly. To clarify, you pulled P11/P12 (which take the L and R amp ouputs to speaker switches) and could apply 120 VAC to the Beomaster without tripping the fault relay? If so, from the schematic, that still leaves the amp outputs feeding the fault circuit so it would mean the problem isn't with the amplifier outputs...and probably not the fault circuit, right?
Or are you saying that with P11/P12 pulled the relay never does anything and doesn't turn on?
In the simulation, with nothing connected to R46 from the L channel amp and nothing connected to R47 from the R channel amp, you should see 14.7 VDC at the IC3 - E, around 13.5 VDC at IC3 - B and somewhere in the neighborhood of 12 VDC at IC3 - C (that depends on the RL1 resistance which I don't know) I'm using around 960 ohms and a 12.5mA turn on current for RL1 in my simulation but I just guessed at those from data sheets of other relays. I was just trying to see what should trigger the fault relay to switch. It doesn't seem like pulling P11/P12 should change anything regarding not having a voltage at IC3 - C.
P11/12, pin 1 and 4 are the 35V+- feed, pin 3 is the speaker. So with the plugs off, I can measure pin 3 on the pcb, 1.5 V. but with the the 35 V feeds disconnected the RL is not triggered, IC3 C is 0 V., IC3 E is 14.7 V
Søren Mexico: P11/12, pin 1 and 4 are the 35V+- feed, pin 3 is the speaker. So with the plugs off, I can measure pin 3 on the pcb, 1.5 V. but with the the 35 V feeds disconnected the RL is not triggered, IC3 C is 0 V., IC3 E is 14.7 V
Interesting still on the IC3 Collector. In my attached picture of the simulator I do not simulate the amplifier circuit or 35 V. I just use 14.7 for the voltage to the fault circuit and a simulated relay. I put an LED as something the relay can turn on and off just to make it easier for me to watch. To simulate a trigger for the fault I experimented with injecting some DC current to see the fault circuit do something. You can see that the simulation has a voltage at IC3 - C without any amplifier circuitry. I know my simulation isn't exact (I checked it a few times and could have some error) but I would expect you to also see some voltage on IC3 - C.
I will connect the speaker pin 3 without the 35 V feed and se what happens, have a power black out now dont know when it will be back, running my computers on no breaks, dont know when power will be back
Power back, tried pin 3 connected, goes to 120VAC RL1 do not trigger, So back to amplifiers, I think the fault switch works like it should.
Søren Mexico: Power back, tried pin 3 connected, goes to 120VAC RL1 do not trigger, So back to amplifiers, I think the fault switch works like it should.
So this test was with 35 volts to amplifiers disconnected but P11-3 and P12-3 connected? Have you tried with one channel connected and one not connected? Also when you say that RL1 does not trigger, do you mean in never turns on (normal on mode)?
I wonder why, if you have P11 and P12 disconnected, you can't measure +35 V on the connector pin 1 and 4? It looks like the RL1 should engage and provide that voltage there. The power to the fault circuit is +15VDC at IC3 - E, the output to RL1 is IC3 - C and the input is the node between R45, R46 and R47. If that input is zero volts then RL1 should be "on".
When you had P11 and P12 disconnected, did you measure the voltage at the R45, R46 and R47 node?
yes 1.45 V
Found something here, When I power up to 120VAC, P11/12 not connected, checking V at TR16 B 1.37V, TR15 B 0.3 mV, then goes to IC3 B, the moment I put my test lead to B on IC3 the RL1 is triggered, stays triggered when I remove test lead and goes back only when I turn off power
Hi Soren,
that the relay triggers if you touch the Base of IC3 is caused by the surrounding electric fields which you inject into the base. These humming (you can hear if you touch the input pins of TAPE or even better PHONO of a working unit) will be amplified by Darlington Transistor IC3 fed back via TR15 to input of TR16. This transistor again triggers IC3 and the positive feedback loop is closed. As a side efect the relay will be activated ;) That's how this protective circuit works.
I think there's a problem with the raise of the supply voltages:
If you supply the whole Beomaster via the variac you wrote at 75 V AC the relay just doesn't get triggered. I guess the ~15V are not yet available at this point. Giving more Voltage through the Variac should give the ~ 15V. The main cause is that the 15 V are regulated in the Beomaster with a 15 Volt Regulating IC (0IC1 on power supply board, LM340-15or 7815). Those Voltage Regulators need at least 3 V more on there input than the regulated Voltage should be. This would be around 18 V. Every thing lower at the input pin can cause nearly everything at the output pin.
I would try the beomaster direct at 120 V AC with the +-35V supply unplugged from the amplifier board just P11-3 and P12-3 connected to see if the relay gets activated or not
Greetings from sunny Munich to Mexico
Ralph-Marcus
Thanks Ramabo, will do, but how do you explain the 1.5 VDC I allways have at P11/12 pin 3 (to speakers), I checked the speaker 1 and 2 switches yesterday and they works perfectly and all connections to speakers jacks even so. Will get to it in an hour or 2..
try the following: unsolder the two resistors R46 and R47 where they connect together and lead to R 45. Now measure the voltage where R46 and R47 have been connected before This gives around 1,5 V i guess. Leave +/- 35 V unconnected to the amplifier for this measurement and don't use the variac.
I think the reason you get 1,5 V is the high impedance of your voltmeter. Do you have an old analog one too? If so try this. Their impedance is mostly lower around (10KOhm/V ~ 100kOhm/V).If you can measure a voltage then it will be lower than 1,5V. Digital Multimeter have an impedance of 10MOhm or more.
Still sunny here in Munich
RaMaBo: try the following: unsolder the two resistors R46 and R47 where they connect together and lead to R 45. Now measure the voltage where R46 and R47 have been connected before This gives around 1,5 V i guess. Leave +/- 35 V unconnected to the amplifier for this measurement and don't use the variac. I think the reason you get 1,5 V is the high impedance of your voltmeter. Do you have an old analog one too? If so try this. Their impedance is mostly lower around (10KOhm/V ~ 100kOhm/V).If you can measure a voltage then it will be lower than 1,5V. Digital Multimeter have an impedance of 10MOhm or more. Still sunny here in Munich Ralph-Marcus
I was thinking about that yesterday, so I will dig out the analog, and try with that, I will leave the R46/47 as is, its a PIB to get at them for desoldering.
Sunny going to 26° in Mex City
Grüss Gott
Checked with an analog MM, the 1.5 V still there.
But, connected with only DBT, and P11/12 pin 3, the RL1 stays disconnected, connected P12, get overload and RL1 triggers, Disconnect P12 and connect P11, RL1 triggers, Connect P11/12, and I'm surprised, RL1 stays put, turned off again, connect DMM over emitter resistors right channel, adjust to 13 mV, do the same in left channel, leave on for 5 min. adjust both channels to 13.9 mV, leave on for 5 min. both channels stays.
Until now I''m happy, will be back shortly
Connected speakers, at speaker 1, hum and DBT comes on bright, connects speaker 2, same hum and DBT bright, connects DMM at speaker1 Left get 65 mV, increasing volume no change, same in right speaker.
Hum eh?