I have been replacing the trimmers on my Sansui AU-D11 mk2, and thought I would write it up as I went along. Despite what I have read, I did not have to separate the sides from the front sub panel in order to replace the trimmers. I did have to do this for a service modification though, this concerns the headphone circuit.
As well as tools, you'll need :
Sansui AU-D11 mk2 Service Manual
2 x 20R top adjustable trimmers, Bourns type 3299W, for F-4263 Equalizer board
2 x 100R top adjustable trimmers, Bourns type 3296Y, for F-4271 Control board
2 x 100R side adjustable trimmers, Bourns type 3296P, for F-4266/7 Driver board
2 x 470R side adjustable trimmers, Bourns type 3296P, for F-4266/7 Driver board
4 x 1K top adjustable trimmers, Bourns type 3296Y, for F-4296 Power Amp board
2 x 120R, 2 watt resistors for headphone service bulletin
Here is the amp without it's top cover, base and front panel. It's pretty straightforward to get to this stage, just remove the screws. As well as screws, The front panel is held in place by the speaker switch and disc selector switch shafts, you can use an 11mm deep socket to remove these, or pliers if you're careful.
The only board where the trimmers are REALLY hard to get to is the equalizer board, which is itself mounted on the control board. To remove this, start by removing the plastic actuator rods that go from the front panel switches to the board. These I have circled in yellow on the picture.
Remove the four screws holding the input connector blocks to the rear panel. Unclip the board from the plastic mounts, and remove the rotary selector switch actuators from the front panel. You should be able to carefully wiggle the board out, you will have to cut a few cable ties and unplug some of the wire connectors. I didn't label these, but you can do to avoid some head scratching later on.
Here are just a couple of the trimmers that need to be replaced elsewhere. I just used a soldering iron and a plunger type solder sucker. Even after you've sucked all the solder off you can, you still might have to heat up a pad while rocking/pulling on the trimmer. Once it's out, if the remaining solder has closed the hole up, take a sharp pencil, heat the pad up, and use the pencil point to make a hole in the solder. You could also use a piece of 24 gauge wire through the other side, keeping it moving about so it doesn't stick. Just take your time and don't overheat the pads on the circuit board.
Each trimmer I took out, I measured the resistance between the wiper and one end. I tried to set the replacement trimmers to more or less the same value. This can be difficult though, as you might remove a 200 ohm trimmer, measure across the whole track, and it might be 185 ohms. Then, you measure your replacement trimmer, and it might be something like 205 ohms. You could work out where the new trimmer needs to be set using percentages, but after trying that for a while, I just set one side of the new trimmer so it matched the same side of the old one.
And that's pretty much it. Just go through replacing each trimmer one by one. The Bourns trimmers I used, invariably don't line up with the solder pads on the board the same as the old ones did, you just have to carefully bend the leads to match. When soldering and desoldering, remember, soldering irons like to burn fingers. And if you've just heated up an old trimmer to remove it, expect it to be hot when it comes out.
You can replace the trimmers on the tone control board without removing it from the front panel. You'll need to position yourself, the soldering iron, and the desoldering gun very carefully. It is possible to do however.
While I had the opportunity, I also re-flowed the solder joints to the upright daughter boards. The picture shows just one such joint, but I did all of them. In order to avoid heat build-up, where there was a group of four, I did the left most joint on each one, then the next one in, and so on. I also added some bypass capacitors across the main power supply capacitors.
As well as tools, you'll need :
Sansui AU-D11 mk2 Service Manual
2 x 20R top adjustable trimmers, Bourns type 3299W, for F-4263 Equalizer board
2 x 100R top adjustable trimmers, Bourns type 3296Y, for F-4271 Control board
2 x 100R side adjustable trimmers, Bourns type 3296P, for F-4266/7 Driver board
2 x 470R side adjustable trimmers, Bourns type 3296P, for F-4266/7 Driver board
4 x 1K top adjustable trimmers, Bourns type 3296Y, for F-4296 Power Amp board
2 x 120R, 2 watt resistors for headphone service bulletin
Here is the amp without it's top cover, base and front panel. It's pretty straightforward to get to this stage, just remove the screws. As well as screws, The front panel is held in place by the speaker switch and disc selector switch shafts, you can use an 11mm deep socket to remove these, or pliers if you're careful.
The only board where the trimmers are REALLY hard to get to is the equalizer board, which is itself mounted on the control board. To remove this, start by removing the plastic actuator rods that go from the front panel switches to the board. These I have circled in yellow on the picture.
Remove the four screws holding the input connector blocks to the rear panel. Unclip the board from the plastic mounts, and remove the rotary selector switch actuators from the front panel. You should be able to carefully wiggle the board out, you will have to cut a few cable ties and unplug some of the wire connectors. I didn't label these, but you can do to avoid some head scratching later on.
Here are just a couple of the trimmers that need to be replaced elsewhere. I just used a soldering iron and a plunger type solder sucker. Even after you've sucked all the solder off you can, you still might have to heat up a pad while rocking/pulling on the trimmer. Once it's out, if the remaining solder has closed the hole up, take a sharp pencil, heat the pad up, and use the pencil point to make a hole in the solder. You could also use a piece of 24 gauge wire through the other side, keeping it moving about so it doesn't stick. Just take your time and don't overheat the pads on the circuit board.
Each trimmer I took out, I measured the resistance between the wiper and one end. I tried to set the replacement trimmers to more or less the same value. This can be difficult though, as you might remove a 200 ohm trimmer, measure across the whole track, and it might be 185 ohms. Then, you measure your replacement trimmer, and it might be something like 205 ohms. You could work out where the new trimmer needs to be set using percentages, but after trying that for a while, I just set one side of the new trimmer so it matched the same side of the old one.
And that's pretty much it. Just go through replacing each trimmer one by one. The Bourns trimmers I used, invariably don't line up with the solder pads on the board the same as the old ones did, you just have to carefully bend the leads to match. When soldering and desoldering, remember, soldering irons like to burn fingers. And if you've just heated up an old trimmer to remove it, expect it to be hot when it comes out.
You can replace the trimmers on the tone control board without removing it from the front panel. You'll need to position yourself, the soldering iron, and the desoldering gun very carefully. It is possible to do however.
While I had the opportunity, I also re-flowed the solder joints to the upright daughter boards. The picture shows just one such joint, but I did all of them. In order to avoid heat build-up, where there was a group of four, I did the left most joint on each one, then the next one in, and so on. I also added some bypass capacitors across the main power supply capacitors.
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