Does anyone have a schematic for Samson TXM16 Powered Mixer?

[dicky96]

Hi guys
Does anyone have a schematic for this? The fault is both protect lights on. I fixed one problem already that was causing the negative rail to both amplifier channels to go to -90V with +45V on the positive rail (It's a class G design)

I now have 45V on both rails +/- but one of the amplifier channels has about 20V DC on all the emitter resistors and it all reads weird because the base of the NPN output transistors is about 8V so they are reverse biased, yet the base of the PNP output transistors reads about 19.3V, so 0.7V less than the emitters so those appear be forward biased but this would then put a negative voltage on the emitter resistors, which is opposite to what I have

Also there is no appreciable voltage drop across any of the emitter resistors so there is no current flowing.

I'm beginning to think the 20V on the output of that channel is coming from somewhere else, not via the output transistors. It could be some fault in the protection detect circuit as that must be connected to (and monitoring) +HT, -HT and the emitter voltage (speaker out) yeah?

Both protect LEDs are still on even though one channel has no DC offset on the output (well a few tens of mV maybe)

The amplifier module is marked 406-TXM20-1712A


See pics and TIA

Rich

[lotas]

Re: Does anyone have a schematic for Samson TXM16 Powered Mixer?

Look, she's not like that.

[dicky96]

Re: Does anyone have a schematic for Samson TXM16 Powered Mixer?

That looks like it could well be the correct one, thank you

[grijan2]

Re: Does anyone have a schematic for Samson TXM16 Powered Mixer?

Here's the complete schematic including the mixer part, just in case it returns to your bench.

Cheerios.

[Loudrichard]

Thank you for the schematic I will try and fix it, the issue is that the power amps both work fine but the channels are not getting to the left master bus. It was fine yesterday, and I am hoping that it might be something simple like a loose edge connector. It did do this once before but then righted itself and has been fine for a year, but then left buss isn't getting to the LR master fader/output meter/Left power amp anymore. Thanks again.

[VoicesFYC]

for the heck of it..i decided to look for info on the problem and found this posting on another site... it would be wise to read it completely ... it MIGHT be a clue https://gearspace.com/board/so-much-...n-circuit.html

Daniel.

[Loudrichard]

Thank you, seems like all these kind of powered units they are OK as long as they work, but servicing is labor intensive as there is a lot to dissemble. And re-assemble! However, I found the fault which was a dry joint and it now works fine. The fault came and went if I flexed the circuit board, so a magnifying glass helped find the culprit, but I touched up the connections in the whole area with proper solder (ie lead not lead free) and now I can't make it go off again so I am happy. The Samson has been a good reliable unit generally, although the claimed 500 WPC is somewhat over optimistic, as usual. Thanks to everyone here for their help.