Amp Transformer Replacement - Trace Elliot Commando 10 65w

pervyinthepark · Post by **pervyinthepark** » 29 Jul 2017, 20:24

Hi, I've been working on fixing up this Trace Elliot Commando bass amp I accidentally burnt up. I replaced a resistor but I'm pretty sure that the transformer is blown from (improper) testing I did a long time ago... no power to on switch anymore. Probably the transformer as I remember seeing sparks on it

I've found schematics here (https://elektrotanya.com/trace-elliot_b ... nload.html) but they don't list the transformer.
It is marked
"75 TRAN[possibly w?]
B65 115V
NOV 2000"
Any idea what I should seek to replace this with?

deltafred · Post by **deltafred** » 30 Jul 2017, 09:07

The on/off switch will be before the transformer so it sounds like the mains supply is not getting as far as the switch.

Check your mains lead and the mains fuse (which could be in the IEEE socket on the back of the amp).

pervyinthepark · Post by **pervyinthepark** » 13 Aug 2017, 17:51

Thank you! I checked the mains fuse and replaced it, the power is back on to the switch. I still get no sound though. So I tested the 4 power transistors using this methodology (https://www.elexp.com/electrical_measur ... art_3.aspx), and it appears all 4 transistors work... The two fuses on the board as well as the mains fuse have all been replaced... and the resistor that burnt up when it broke initially... wondering where else to go from here? I cross-posted this to Amplifiers back in April (been on this a while...) and here are the imgurs from that thread. The burnt resistor pictured has been replaced.

deltafred · Post by **deltafred** » 13 Aug 2017, 18:25

Have you checked the power supply voltages across the smoothing capacitors,

C11 and C15 - 4700uF - the voltage isn't specified on the schematic but my guess is about 32V to 35V (for 65W into 8ohms).

C13 and C21 - 220uF - should be about 15V across each.

pervyinthepark · Post by **pervyinthepark** » 17 Aug 2017, 02:55

It seems everything I touch is getting about 4.2V. So it must be the big guys C11 and C15? Since I need it on to test I can't direct test the caps so I tested via R22 and R31 next to it, then started testing other things. Everything was 4.2v

deltafred · Post by **deltafred** » 17 Aug 2017, 08:06

4.2v to where?

Try this.
What are the DC voltages across Z1 and Z2?
If these are around 15V then the power supply is (probably) working fine.

pervyinthepark · Post by **pervyinthepark** » 19 Aug 2017, 00:18

Woops I was on the wrong voltage setting.
I just did DC voltage testing on Z1 and Z2 from ground and got 0V...

deltafred · Post by **deltafred** » 19 Aug 2017, 07:54

OK, set your meter to the AC volts on a high range (as it could be somewhere between 50 and 100v) and measure the voltage between fuse F1 and F2, either end as long as the fuses are good.

If the mains fuse is ok and your meter reads 0v then it looks like your transformer is dead.
If there is AC voltage there then the next things to check are the bridge rectifier and R22 and R31.

As always, fault finding over the net is difficult and there is no substitute for having the faulty item in front of you.

pervyinthepark · Post by **pervyinthepark** » 26 Aug 2017, 02:49

Uh it just lit up the electro caps and transformer next to it and made a sound I'm scared

deltafred · Post by **deltafred** » 26 Aug 2017, 08:11

It sounds like you may be out of your depth on this.

If you want it working again probably best to find a competent amp tech before you do any more damage to it.

There is nothing worse for a tech than taking on something where a well meaning tinkerer has been in trying to repair it. Before you can fix the original fault you have to find and correct all the faults and changes that they have introduced so it ends up costing them more.