These three items (Q401, 402 and 403) are, I believe, transistors. Correct? Each has three legs. I suppose they are A, B and C, though I do not yet know which is which. The actual wire legs of these things are hard to access from the top, so I was measuring at the solders underneath. Do I need to try to measure at the wire 'legs?'

In this diagram, the patch in the lower left of the red circle, involving one leg of C313, "AA", two legs of Q402 and one leg of Q401, the voltage is 25.38.This should be -22V or so, not +22V or so as you measure, you sure you did not reverse the probe. Double check.

In the patch in the center which, I discern/guess includes the E leg of Q402 and the B leg of Q401, the voltage is .767.This is point "A" in my schematic, it should be -15.7V. This is wrong.

In the patch in the lower right corner of the red circle, which includes the final leg of Q401, one leg of R401, R227 and R233, there is 1.232 volts.

The patch in the upper right corner of the red circle, which includes the B leg of Q405, has 7.59 volts.

In the upper left corner, containing the E leg of Q405, there is no voltage (0.002).

Click to expand...

I want to verify this is what you measured:

Check again and make sure you have the meter measuring the correct polarity. The first one cannot be +25V, got to be -25V. Read the response in BLUE above.

If the two legs of Q402 is -25V and the rest is correct, I think the Q402 is bad.

You have any resistors? I am sure you can buy some resistors in stores like Radio Shack, Fry's or any electronic store. If you have a store like this, buy a 4.7K 1/2W resistor, get the cheapest one. Connect between the 2pins patch of Q402 to the single pin patch of Q402.( literally across the Q402). Turn on the amp and measure the voltage, you should get somewhere around -15V.

Q402 is just a current sink to pull about 6mA from Q403, I am using a resistor to pull current instead of Q402. If Q402 is burned open, the resistor will help pulling current and make the circuit work. Below is the the added resistor.

This should be -22V or so, not +22V or so as you measure, you sure you did not reverse the probe. Double check.
Yes. My bad. -25V

This is point "A" in my schematic, it should be -15.7V. This is wrong.
This is +.768. Should be -15.7, you say.

I see you are recommending use of a resistor to, basically, do the work of the failed Q402. I can do that, but I wonder why I wouldn't just replace Q402. I am concerned that I am hoping that two wrongs will make a right. On the other hand, it sounds like you are asserting that the use of a resistor here would do the same thing as replacing Q402, but also be more reliable. If so, then that would make this a good plan.

I wonder why you would have me test it with one resistor but actually repair it with a different resistor value.

There once was a nice electronics supply store in my area, plus multiple Radio Shacks. No more. The nearest resistor for sale in my area is quite a distance. Since I need some caps anyway (the power supply filter caps are visibly bad), and I need stuff like solder and solder wick, etc., I am hoping to make a list of items needed and just order them. I am patient.

I am tempted to include most or all the other capacitors in the order. Once this thing is at least up and running, I gather that a recap is a good idea. Right?

I know that I can increase the capacitance of the filter caps. In one recent thread here, the poster used 6800uf Nickicon caps in place of these Mallory 3000uf units. Another guy used 10,000uf caps! I wonder if, in replacing the smaller caps on these boards, I should stick to the original capacitance specifications or, alternatively, whether I can increase those values.

And finally, the 6800uf Nichicon caps have both terminals at one end. The Mallorys have one at each end. I have shrink tube and I can also use a bit of more rigid plastic tubing and some bus wire to address this and help secure the new caps. Does this sound like a good plan, or should I find caps configured like the Mallorys?

Honestly, I don't mind spending the money to get parts. Electronic parts are pretty inexpensive.

Resistor is a quick and dirty job. If you have the order order the Q402 by all means. But remember, this is just a guess, I might be wrong that Q402 is the problem. But it looks like it and Sregor said it's common for Q402 to fail also.

You can recap particular some looks like it's leaking. Don't increase the value, just find the same or closest value ( a little higher is ok). Or else, you have to put some protection circuit for the power switch.

What other thing is wrong while you are on this. I was hoping you have a resistor to make the -15V work, then continue to troubleshoot down the chain. You have a friend that can give you a resistor?!!!

Yeah, I suppose I could get a resistor from a friend. Do that first, then continue troubleshooting.

As far as other problems with this unit.....I have no idea. The only part of this unit that works is the LED "Power" light. Otherwise, it is 100% dead. Transformer seems to work though, so I suspect it can be brought back to life. I am told these are nice units, when working.

I concur with Alan that the best course is to try the resistor fix to see if the unit will start working. It's a brilliant move (I'm learning a lot here as well).

The idea of replacing most of what is in the +/-15V circuit is likely a good one, when the time comes. This circuit has been implicated in fixing a hiss problem that is not uncommon in the Advent 300 as they age. There is a longish tread on this topic (http://audiokarma.org/forums/index.php?threads/fixing-hiss.224898) that has a number of twists in it and can be discouraging to read at times; the hopeful take home is that a few of the components in the +/-15V can play a role, but especially the RA400. What is discussed there, from page 5 or 6, is that even if the RA400 is putting out the proper +15V voltage (as yours seems to be), it can be a source of hiss for those units that have developed hiss.

None of these parts are expensive, so it makes sense to order all at once to save on shipping, but you want to be at a place that you can better assess your needs (i.e., after you hopefully get it running with Alan's resistor trick). I have notes on possible replacements for the RA400 for when the time comes.

Oh, and on the PS caps, when you order, you can use either axial (like the present Mallory caps) or radial. I used radial on mine because that is what I had on hand, but it would have been much easier to install using axial (the radial requires soldering in extra hookup wire to the leads to be able to reach the solder points, which the axial do not require). Axial is what I would order if they are available. There are many other caps on the Advent boards that are axial; these are also much easier to replace with axial wherever possible.

You can go to higher capacitance for the PS caps, but I agree with Alan that not too much higher; I would not go higher than 4700µF. On non-PS caps, you should stick with existing values, as circuit behavior may depend them.

However, with all caps, feel free to go as high as you like on the voltage rating, as long as the cap does not get physically too large for the space. For the small caps, I keep a reserve supply of 50V caps handy for convenience and simplicity, and regularly use them as replacements for lower voltage 16V, 35V, etc. caps.

Excellent! Northpaw's answers to my questions are precisely what I wanted and Alan's suggested patch fix is a great idea for now, to see if this thing will come to life. A local friend says he has a 4.7K-Ohm resistor. I will grab that today if I have time. Then, I will be gone for a week, playing in the Sun and water in my home town with my family. When I return, I will resume. I will resume with confidence that, with your help, I might make some good progress in this project. Slowly. You guys have been great. Thank you.

At this point, I think RA400 is working, don't just go out and change it right now. Get the -15V back, a lot of things will start working. The power amp and phono and a lot of others need the -15V, that's why everything is not working. I am not saying you don't have other problems, I just say getting back the -15V will make a lot of things start working again. That time, we'll see what else more to fix. Hopefully that's it.

I've been sitting back watching this one and I have some advice as I was the one that figured out the hiss problem on these was in the 15v regulated circuits.

First piece of advice: change the three transistors for the -15v circuit with new components of the same value and also replace RA400.

Second piece of advice: I would RECAP THE WHOLE UNIT. By now EVERY cap in it has aged to the point of being useless. I'm speaking from personal experience on several of these Advent 300s now. If a fuse was blown in the unit, chances are there is a shorted output transistor, but possibly not if you have issues with the 15v regulated circuit. Either can cause a fuse to blow. If the power supply is working as it should and you've replaced the caps, no need to replace it (BR1100) although I have had one that was shorted before, it is not that common of a failure. Even if you want to use this as a preamp only, you still need the power amp section working trouble free to not have issues with the whole receiver.

I can't stress enough that just recapping a section of one of these is not enough. The whole thing needs to be recapped. Advent used just barely good enough parts in it because they were selling it to a certain price point. Read that as budget parts for the best sounding budget receiver ever marketed.

I say get the -15V working first. The +15V is working, I would not just go and change the 78M15. I see no symptom that Q401 and 403 is bad. All I see is if Q402 stop sinking current, the voltage is going to be like what he measured. There is no reason to change Q401 and 403 yet.

You don't want to change everything at the same time, you can make a mistake and cause new problems and mask your train of troubleshooting. At most, change ONLY the caps that are leaking as they are obviously bad. One thing at a time, have it working, that serve as a new starting point and then do the other things.

There is a thread where the person took a working amp and change out transistors and all and now it's not working. Don't assume anything is bad until you see the symptom.

Look at the schematic and find the problem. When -15V is up, a lot of things will be working, change out the leaking cap, then go from there. I intend to fix the whole amp, just one step at a time.

AND more important, if you start taking the amp apart, TAKE PICTURES step by step where the wires go, how they layout. Take pictures every step so if anything goes wrong, you can retrace the wires using the pictures.

A friend gave me the resistor, and also a couple of 1000uf radial caps. He suggests using the caps to temporarily replace the failed filter caps, for testing purposes. My cheap soldering iron (rated at 30W) has a fat tip. As I have reported, I am new to this and VERY hesitant and careful. I could install these bits, and probably not screw anything up and probably not damage the board, but for the moment I am hesitating. Here are some pictures. There is a big board and a small one. The first close up pic is from the big board. The rest of the closeup pics are from the smaller board. I hope to get your thoughts and observations. In particular, I wonder if these closeup pics represent modifications to this unit or, alternatively, whether they might be factory original installations of wires and parts onto the back of these boards. In one pic, the wire insulation appears to be melted. Overall, this makes me wonder whether I really should be trying to salvage this unit.