Line 6 Vetta II HD Power Amp Repair

[CyberChrist]

Hi, everyone! I need help with power amp repair. I owner of Line 6 Vetta II Head unit. And bought her with non stable work with power amp. After purchase I testing power amp with my headphones (Sennheiser hd 280 pro), but volume level was not stable. After 15 minutes of testing this head destroyed my left chanel in headphones and stoped sounded. But from another outputs (for recording, 6.3mm) Vetta work fine. Today I start repair power amp module, looking at schematic in HD147 https://www.docdroid.net/lAQa1GW/hd147-service-manual-pdf



What do you think about this? Which element should be checked first?

[Jon Snell]

Are you conversant with Class D amplifiers ... you need a good quality double beam/channel oscilloscope and a DVM that measures RMS voltages; Fluke etc.
Replace the insulating pads and refit the amplifier on its heat sink. It is not a good idea to re use old pads.
Check if the amplifiers are oscillating when power up with no load. No oscillation on the output is not good news but it looks like you had no smoke.
Check the power supply is correct both high voltage and low voltage for the controls.
Read the service information and follow the circuit on the faulty channel from the output section back in until the fault shows up.

[CyberChrist]

Are you conversant with Class D amplifiers ... you need a good quality double beam/channel oscilloscope and a DVM that measures RMS voltages; Fluke etc.
Replace the insulating pads and refit the amplifier on its heat sink. It is not a good idea to re use old pads.
Check if the amplifiers are oscillating when power up with no load. No oscillation on the output is not good news but it looks like you had no smoke.
Check the power supply is correct both high voltage and low voltage for the controls.
Read the service information and follow the circuit on the faulty channel from the output section back in until the fault shows up.

No. I hadn`t smoke. But power amp had much hot.

[Jon Snell]

A simple test. If you test the output FETS and they read OK, it is probably working and you had a short circuit headphone lead.
As I said, DO NOT replace the board without replacing the insulating pads!

[CyberChrist]

A simple test. If you test the output FETS and they read OK, it is probably working and you had a short circuit headphone lead.
As I said, DO NOT replace the board without replacing the insulating pads!

Dear Jon Snell. Simple test like this is correct?

[Jon Snell]

Not sure what your meter means but if the FETs are OK, the odd are it is probably OK.
If you are not sure how to test a FET have a look on the gargler (google) for ways to check them.

[CyberChrist]

Not sure what your meter means but if the FETs are OK, the odd are it is probably OK.
If you are not sure how to test a FET have a look on the gargler (google) for ways to check them.

Ok, I need to search more information about correct check of FETs in Google. Please, wait about 24 hours I will study this technical question. Thank you

[CyberChrist]

I`ve checked all IRFP250N on plate watching this video https://www.youtube.com/watch?v=uLouCcG58Uo

But all of this elements show about (0.?)500 v(?) x8 mosfets on plate

Can I speak that this elements works fine?

[CyberChrist]

At facebook search I`ve seen Vetta II HD power amp repair example. Can this photos help?
https://www.facebook.com/datorelectr...69530469969436

[CyberChrist]

Once again I tried to turn on the power amplifier, using the outputs to the cabs (not using headphones), but I didn’t get any sound, in the maximum power mode the board does not heat up at all

[Enzo]

In photo #4 just above, I see a white 4-pin connector with no mate plugged to it. Is there a missing connection?

[CyberChrist]

In photo #4 just above, I see a white 4-pin connector with no mate plugged to it. Is there a missing connection?

No cable for this slot. At vetta II you can see 3 empty slots for 4 and 6 pin connectors. See examples at photos

[Jon Snell]

Once again I tried to turn on the power amplifier, using the outputs to the cabs (not using headphones), but I didn’t get any sound, in the maximum power mode the board does not heat up at all

A class D amplifier should stay cold and only warm up when working hard into a heavy load.
The output transistors are either on or off, so little waste of power.

If you are not fully conversant with how FM, Class D amplifiers work, get a service centre to fix it.

[CyberChrist]

A class D amplifier should stay cold and only warm up when working hard into a heavy load.
The output transistors are either on or off, so little waste of power.

If you are not fully conversant with how FM, Class D amplifiers work, get a service centre to fix it.

I'd be happy to send it in for repair. But there are no such specialists nearby. I will continue to learn how to fix it myself, there are no options. Even if I don’t fix it, I’ll put an external power amplifier unit and that’s it. Everything works fine in amp bypass mode.