HotSetup T300 Orion

[Dr Zeus]

Got this amp in which had failed BP912 outputs on one channel. Replaced with 2n6491. New emitter resistors.

I cannot get the amp to power on, and theres something wrong in the PS. The amp draws 0.08A with just B+ and ground connected, then only draws 0.13A adding REM. Not powering up.

I changed out the TL494 and a close-by C81 10uf cap that looked leaky. That did not help.

TL494:
1. 0
2. 0.061
3. 0.061
4. 10.88
5. 1.476
6. 3.356
7. 0
8. 14.20
9. 0
10. 0
11. 14.20
12. 14.20
13. 4.95
14. 4.95
15. 0.061
16. 0.009

Is there something like a cap shorted somewhere you think?

 

[Dr Zeus]

I removed D26 which seems fine and the amp tries to power up but with excessive current draw, even with rectifiers removed. Ps fets warm up. The signal on the gate of the ps fets looks clean. I may try removing the fets here...

 

[Perry Babin]

What's driving pin 4 high?

What does D26 do in the circuit?

Have you tried twisting the transformer to see if it's intermittently shorted?

 

[Dr Zeus]

Definitely a bad transformer. I had a parts Orion Xtreme400 that had a similar transformer. Installed and the amp seems to be working +-30vRail with rects installed. The only thing is, the Xtreme400 transformer is about 10% larger than the original T300. Amp powers and will probably play. Photo next post.

The original transformer is shorted across ALL legs; off the board. Without un-winding it, cant really tell where its actually shorted.

D26 connects from Secondary CT to several caps in the PS; Mainly C82, C81, a resistor close-by, and then back to Pin #4 of the TL494. I had removed D26 last night because was trying to figure out why pin 4 was high as you then mentioned.

 

[Dr Zeus]

Transformers. T300 on the right vs X400 installed.

 

[Perry Babin]

The power supply appears to be regulated so without forcing it to full drive (or counting the windings), it would be difficult to compare the transformers for voltage. Even then, you'd have to count the primary and secondary windings on the old transformer to know how different they are.

 

[Dr Zeus]

Its not regulated. Unless changing out the transformer or something else has failed, its always running full duty. Rail voltage changes slightly on input voltage changes.

Amplifier works otherwise.

 

[Perry Babin]

If this is like orion amps, it's not PWM, it's PAM and the duty cycle doesn't change. The amplitude of the drive waveform changes.

 

[Dr Zeus]

Yes it’ll Pam. Rail voltage stays steady. Seems the xtreme400 transformer is going to work out. Bench tested to clipping pulled 40a at 4 ohms. Seems about right for a ~300w amp and it’s staying all together. I’ll call this one fixed.