It is safer to start up with R108 being 560R-562R. Let her rip.
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Nah somethings not right there I suspect. Where is Q103 located? What bias options for resistors were used?
Q103 is located right between the center two outputs. Q103 and Q104 are BD139. 562R was used for R108.
pres/drivers/outputs combo? @anatech does have a solid point, and it could be that, it just seems very unlikely. Could be the one off, but this board has had problems right, and then you find the bias pot needs to be absolutely pegged to the end in order to get the right bias current?
I mean, you seem to have got on top of it, which is good, but is it a sign of things to come? I'm not even close enough to the level of the build team to be qualified to say so but of the six boards I've done with almost every possible combo of pres, drivers and outputs I don't think I've ever had R109 past maybe 4/5ths of its range.
I mean, you seem to have got on top of it, which is good, but is it a sign of things to come? I'm not even close enough to the level of the build team to be qualified to say so but of the six boards I've done with almost every possible combo of pres, drivers and outputs I don't think I've ever had R109 past maybe 4/5ths of its range.
Fully encapsulated? Sorry if stating the obvious, its just the first google result for me at least is an exposed back model from STM
@Mainframe, you are right. It is still acting crazy. It continues to creep up and when I had it at about 31mV it jumped up to 41Mv, then right back down. So the question is what would cause this? I tested Q103 and Q104, but that doesn't mean one of them isn't bad.
Is there perhaps a cold/dry joint somewhere? Hmm try the old pencil eraser on components. 🤔
Is the rail voltage fluctuating wildly when it happens? You had issues in a cap multiplier area, perhaps if a cap multiplier was failing in and out it would make the rail jump around and with it the bias. Food for thought anyway
Is the rail voltage fluctuating wildly when it happens? You had issues in a cap multiplier area, perhaps if a cap multiplier was failing in and out it would make the rail jump around and with it the bias. Food for thought anyway
Are you doing this with input leads attached or a shorted input?
Are you testing this output board with an input connected or with resistors between rails and PD+/ND-? If using an input board, try another one. VAS current of the input board may be unstable.
This is initial startup with the IPS installed. The input connector was not shorted. The potentiometer was replaced. I will try it with input shorted first, then I do have another input board. I will try it with the other input board. All the input boards were tested in isolation and all the EF3-3 boards were tested in isolation.
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I have never seen anything like this. Without the cover on it kind of stabilizes at 21mV. Put the cover on and it immediately jumps to 40-46mV. Touch the lid and it jumps down intot he 30mV range, take your fingers off, jumps back up to 40-46mV range. Watch the video below.
Unplugged power to the other channel and it not as drastic, but still moves about 1mV when just touching the front panel and cover.