Troubleshooting AVT150 after fan replacement; why did the fuse blow?

lack

New Member
Joined
Jun 16, 2022
Messages
3
Reaction score
1
Hi! I'm pretty new to DIY amp repair, and thought I'd take on something pretty simple - I have an "AVT150 valvestate 2000" and one of the fans was getting pretty noisy, but otherwise working perfectly. I got a replacement fan and took the unit apart. Replaced the fan. No big deal, I thought. But when I plugged it in again after reassembly, the fuse blew immediately. I have no idea why!

Some maybe relevant facts:

1. During the disassembly, I disconnected the power amps from the main board, just so I could remove the heat sink where the fans live. I'm 99% sure I reconnected them in the right order, but if I reversed those connections (labeled CN102 and CN103 on the board) would that connection order matter?

2. With the power amps disconnected, I did plug it in and turn on the main power, once to check which fan was the noisy one, and again after replacement to ensure I got the fans wired back up right. Everything looked fine, and I was careful not to short anything out when I ran it that way, holding the heatsink component and disconnected power amps far from the body of the unit. Would powering the unit without the power amps connected be enough to cause the fuse to blow later (after I plugged them back in?). Both times everything seemed fine and the fans spun up as expected.

3. When I got it fully reassembled and powered up, I saw a small puff of smoke come out of the top, but since I had the unit fully assembled at the time, I'm not exactly sure from where it came. The tube looks fine (I think). All ICs look fine (i think). Could the fuse itself be the cause of the smoke, or is it likely some other component?

So what do I do now? I'm thinking I'll replace the fuse once and power it on once again, with the amp out of the cabinet, just to see if I see anything obvious before the fuse blows again. Should I try anything else?
 

Dogs of Doom

~~~ Moderator ~~~
Staff Member
Joined
Aug 2, 2012
Messages
27,788
Reaction score
39,137
Location
Los Angeles
before you replace the fuse, give it a good visual inspection...

Where there was a puff of smoke, there's probably some soot somewhere.

If you just put in a new fuse, you risk another puff of smoke.
 

lack

New Member
Joined
Jun 16, 2022
Messages
3
Reaction score
1
before you replace the fuse, give it a good visual inspection...

Where there was a puff of smoke, there's probably some soot somewhere.

If you just put in a new fuse, you risk another puff of smoke.
So far the only soot I see is inside the glass of the fuse itself, but I'll double-check before I try again. Thanks!
 

South Park

Well-Known Member
Joined
Sep 14, 2019
Messages
3,988
Reaction score
3,852
something is grounding out the board is touching something or something you hooked up .
 

lack

New Member
Joined
Jun 16, 2022
Messages
3
Reaction score
1
Thanks to both of you!

I double-checked everything, and I did see that one corner of the main board wasn't fully seated on its peg, so it was a bit higher that it should have been. Maybe one of the components under the heat sink could have been a bit too high and grounded out on the heat sink itself? At least that's a possibility... I'll take it apart again and check over the components in that area for distress before I try again.
 

Latest posts



Top