Hello, I'm currently trying to repair a Luxman L-3 that I bought at a thrift store to make it mine and enjoy! For now I've read all the previous posts made on this forum and though I found the issue when I changed a resistor that was problematic for someone else (mine also was bad). Replaced the resistor with one that was good (Amazon) and tried to turn it back on... ohoh the dim light tester stays on.
That was my initial try at repairing it, since then, I tried to find the short, but I can't seem to find anything promising. I used a thermal camera to identify hot spots on the power board and found to spots, one around the D403 and D404 diodes and the Q408a area. Since then I pulled all the components to test them outside the circuit, but they all seem to be good from my understanding.
I'm kinda lost and don't know what I could check before starting to resolder all the components back on the board, do you guys have any wisdom to share that could help me with my project! Thanks. There seems to be a good amount of info on this site about the amplifier so if you want something specific let me know and I'll share it with you (schematic, components list, voltage drop of the components I pulled, etc.).
That was my initial try at repairing it, since then, I tried to find the short, but I can't seem to find anything promising. I used a thermal camera to identify hot spots on the power board and found to spots, one around the D403 and D404 diodes and the Q408a area. Since then I pulled all the components to test them outside the circuit, but they all seem to be good from my understanding.
I'm kinda lost and don't know what I could check before starting to resolder all the components back on the board, do you guys have any wisdom to share that could help me with my project! Thanks. There seems to be a good amount of info on this site about the amplifier so if you want something specific let me know and I'll share it with you (schematic, components list, voltage drop of the components I pulled, etc.).
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What "high" voltage did you see at the spkr terminals.
Near rails voltage might point to failed output or driver or... transistors.
One or both channels affected
Once repaired, consider fitting one of those protection kits available on the bay or the diystore or...
Near rails voltage might point to failed output or driver or... transistors.
One or both channels affected
Once repaired, consider fitting one of those protection kits available on the bay or the diystore or...
The voltage was ±37 V at the terminals for both channels, after changing the resistor (R406 which was reading 0.9 M ohm) the voltage was at ±10 V but with the dim bulb lighting up (60W bulb).
With R406 stressed it is suggested to check downstream components, ie, zener DZ401a, check cathode voltage, nominal +19Vdc?
I didn't test the voltage initially at the zener diode and now I got a bunch of components off the board, could I remove the zener and test it with a multimeter?
Yes you could use the diode test function on your MM, test both orientations, expect 0.6V and OL, however the best test is under load/in circuit by measuring the voltage at the node common to DZ-401a/R403a/R406a, ie, measure Vdc at either of these components will suffice since they are all connected.
Got too much components off the board so I tested it them outside the board with this setup! Tried to test it in diode mode first, got 0.789 V and OL the other way around. A little bit higher then what you told me so decided to test load it.
Got this setup going, 3x 9V batteries in series with 1.5k ohm resistor in series to get close to the 19.25 V it's rated for. Everything seemed to be fine, reading about the same voltage drop at the diode. Then tried with something a bit more powerful, 27.6 V (no resistors) and got a reading of 23.2 V, shouldn't it be staying around 19-20 V max? Also it burned some of my plastic leads so I'm guessing it's getting hot. Could that mean that the diode failed?
If so what can I replace it with? Got any alternative you know? A quick search gave me this on digikey ; https://www.digikey.ca/en/products/detail/nexperia-usa-inc/NZX20A-133/2119733
Could that work?
Got this setup going, 3x 9V batteries in series with 1.5k ohm resistor in series to get close to the 19.25 V it's rated for. Everything seemed to be fine, reading about the same voltage drop at the diode. Then tried with something a bit more powerful, 27.6 V (no resistors) and got a reading of 23.2 V, shouldn't it be staying around 19-20 V max? Also it burned some of my plastic leads so I'm guessing it's getting hot. Could that mean that the diode failed?
If so what can I replace it with? Got any alternative you know? A quick search gave me this on digikey ; https://www.digikey.ca/en/products/detail/nexperia-usa-inc/NZX20A-133/2119733
Could that work?
