Line 6 Vetta combo power supply

[Delta362]

I'm working on a Line 6 Vetta combo that came with with the complaint of no power. When I opened it up, I found that C18 had exploded and C19 measured bad on the power supply board (page 13 [35-00-0096]. I replaced those. I could not find any other failed components on that side of the power supply, nor any failed components on the power amp output board (pages 10-12 [35-00-0095]. I could not find the source of why these caps failed.

Then I looked at the front end of the power supply and found Q3 and Q15 shorted, R21 burned open, along with a host of other components (R21, R7, R55, R49, R12, R11, D4, Q3, Q15, Q11, Q2, U2) that were bad. These components all fell in line with the service manual list of other component to replace when these two FETs are shorted (page 88 of 95).

I was able to replace all of those and the amp worked fine for about 10-15 minutes. At that point, the amp shut off and upon inspection, the same front end components failed again (Q3, Q15, plus the same host of other components). Any suggestions on what I overlooked? Maybe damaged the D2PAK Q3/Q15 during installation with too much/long heat? Something on the load side of the power supply still bad? Other? Thanks!

[Jon Snell]

Check the tuning circuit R17, 18, 20, C22 and D17.
Good luck with finding genuine NTB10N60 as they were obsolete some years ago.

Line6 only supply panels, they don't supply to component level, as far as I am aware.

[Delta362]

Thanks for the tuning circuit suggestion! I'll check that out.

As for the NTB10N60, I had substituted it with Infineon IKB10N60T from Mouser. Was that a poor choice? [yes, poor choice as the devices are different types] Perhaps there's a different substitute to use? Is there a circuit tweak that I may need to do to account for this one?

[Delta362]

Is the IKB10N60T a good match when looking at the datasheet compared to the original Onsemi? No!

Looking at the Onsemi datasheet for the NTB10N60, its recommended replacement is the Fairchld FQB12N60, which is also discontinued. According to the Fairchild datasheet, that crosses to STB9NB60-1 (also obsolete). Would the STB13NK60ZT4 be a suitable current offering? It looks like it's higher current, but the STB13 has a back to back zener clamp between the G and S, which is not on the STB9NB60 version. Concerns?

Edit: Maybe the STB10NK60ZT4 is a closer fit? Also added the Onsemi datasheet

[Delta362]

I did a lot more checking out the datasheets and realized that I mistakenly substituted an IGBT instead of the MOSFET as the part numbers looked oh so similar. Definitely was a mistake on my original substitution.

I'll order the STB13NK60Z devices to replace the NTB10N60 along with replacing the other failed components. I'll also check those tuning circuit components as well.

[Delta362]

R20, R17, R18 measure 18.4k, which makes sense given three 56k are in parallel. Diode D17 is not shorted. However, as I look at T2, this appears like it may have overheated. I noticed some discoloration on the yellow insulation wrap. Thoughts?

[Delta362]

Got the correct MOSFETs installed and replaced the same failed components (R21, R7, R55, R49, R12, R11, D4, Q3, Q15, Q11, Q2, U2) as last time. However, when I powered it on, it immediately blew the 0.22Ω R21, Q3, Q15, plus the rest of same components. Obviously I missed something. Any guidance on what would cause these to blow immediately on power up? Before I order and replace them again, what other things should I be looking at?

[Delta362]

I also did check the tuning resistors, which were fine, but did replace D17 and C22 as precautionary, with my thinking that they were stressed during the prior fault.

[Delta362]

Got it resolved. I replaced the same components as last time and carefully inspected to make sure I had no poor solder joints or stray solder.