Advent 300 Rebuild: Let the jaws hit the floor, let the jaws hit the flooooor!
- Thread starter patfont
- Start date
Coupling capacitors, mostly 1uF and 10uF parts, have a high rate of being in really bad condition on this model. There are several on the tuner circuit board, near the rear panel, which is the vicinity of the stereo decoder chip. If FM is the only source that you're unhappy with, you might start by replacing the caps in this vicinity.
Let me have a look.
Hi all,
I got one of these with a lot of issues. I’ve been reading through this thread, and my first question is: how difficult is it to remove the boards in order to replace the small capacitors and other needed parts?
That is the part that would stop me the most. I’m considering replacing only the power supplies and leaving the rest as it is, using it as a preamp.
The radio only works in mono, though. The phono sounds quite good (it has the hum that I think needs the underneath strapping fix). I’m not concerned about the amplifier side for now.
I have ±15 V and ±11.5 V on the phono board. The voltage across the rails is approximately 51 V, and it should be 44 V, but I guess this is a common problem with the mains voltage increasing from 110 V AC to nearly 120 V.
I hope there is still someone interested in this topic, as it is quite old.
Manel
Edit:
Oh, I just realized that maybe the bottom panel comes out, which would expose the other side of the PCB to allow desoldering.
Second Edit:
I got lucky. I replaced the 1 µF 50 V capacitor (C911 or C912), and now both tuner channels are working.
I lifted one lead on each capacitor to measure them. One measured 1.2 µF, while the other measured almost no capacitance, so the fault was easy to find. I don't know much about radio tuners, but after looking at the schematic, those two capacitors seemed to be associated with the left and right channels.
I got one of these with a lot of issues. I’ve been reading through this thread, and my first question is: how difficult is it to remove the boards in order to replace the small capacitors and other needed parts?
That is the part that would stop me the most. I’m considering replacing only the power supplies and leaving the rest as it is, using it as a preamp.
The radio only works in mono, though. The phono sounds quite good (it has the hum that I think needs the underneath strapping fix). I’m not concerned about the amplifier side for now.
I have ±15 V and ±11.5 V on the phono board. The voltage across the rails is approximately 51 V, and it should be 44 V, but I guess this is a common problem with the mains voltage increasing from 110 V AC to nearly 120 V.
I hope there is still someone interested in this topic, as it is quite old.
Manel
Edit:
Oh, I just realized that maybe the bottom panel comes out, which would expose the other side of the PCB to allow desoldering.
Second Edit:
I got lucky. I replaced the 1 µF 50 V capacitor (C911 or C912), and now both tuner channels are working.
I lifted one lead on each capacitor to measure them. One measured 1.2 µF, while the other measured almost no capacitance, so the fault was easy to find. I don't know much about radio tuners, but after looking at the schematic, those two capacitors seemed to be associated with the left and right channels.
Last edited:
Welcome to AK!
To reduce dependence on luck, replace (at least) ALL of the 1uF and 10uF capacitors. I'm generally not a big proponent of speculative re-capping, but in this model I think it is warranted. Even if you only plan to use it as a pre/tuner, I believe all of the 1 & 10uF caps are in that signal path. And they are all bad, or will be.
Thanks, everyone!
Yeah, I'll replace all the electrolytic capacitors eventually, but I don't have all the required values and footprints on hand. I also can't resist troubleshooting while I wait for an order to arrive , it's part of the fun.
Another thing I plan to do is replace any electrolytic in the signal path with film capacitors, at least in the phono, preamp, and tuner sections.
I've already replaced the 1 µF 50 V capacitor at the phono input and tested it.
That may make it a little less original, but I don't mind.
This unit already has the strap underneath the phono board.
Update
It's been a few months of using the Advent 300 and I'm super happy, no issues at all.
After the tuner channel fix and recapping some of the small electrolytic, everything is working fine. I measured them as I was swapping them and only 2 were bad. So after a good number of them (around 20–25, it's been a while), I stopped chasing the rest. Especially because they were a bit harder to reach.
I haven't replaced the big caps in the power supply. As I said, I even forget what I did to decide whether they were still good or not, but there's zero hum, best vinyl listening ever, and also sounds great through AUX with my laptop connected.
While soldering one of the new caps located really close to the edge, near the chassis (bad reach/visibility), I accidentally shorted a lead and the magic smoke appeared. I had to replace Q117, which is a 2N5087 if my memory serves me right, and also changed the Zener diode in the transistor's base bias circuit. Just mentioning it in case anyone runs into the same problem.
It's been a few months of using the Advent 300 and I'm super happy, no issues at all.
After the tuner channel fix and recapping some of the small electrolytic, everything is working fine. I measured them as I was swapping them and only 2 were bad. So after a good number of them (around 20–25, it's been a while), I stopped chasing the rest. Especially because they were a bit harder to reach.
I haven't replaced the big caps in the power supply. As I said, I even forget what I did to decide whether they were still good or not, but there's zero hum, best vinyl listening ever, and also sounds great through AUX with my laptop connected.
While soldering one of the new caps located really close to the edge, near the chassis (bad reach/visibility), I accidentally shorted a lead and the magic smoke appeared. I had to replace Q117, which is a 2N5087 if my memory serves me right, and also changed the Zener diode in the transistor's base bias circuit. Just mentioning it in case anyone runs into the same problem.
Last winter I fought with a 300 , off and on, for a couple weeks. Eventually found an open resistor in the preamp. During the process I bought one of the transistor kits. Got the pin out wrong on one. Finally got it figured out. In the process a couple tracks got damaged and had to be repaired. I was ready to drop kick it, but somehow found the inner strength to hold off.
Been there, done that.
All good now!
Thanks for the kind offer. I'm a bit lazy to take it apart. I'm pretty sure they are original. They look like in this picture:
