HSU VTF-2 Power Supply Rebuild - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 3 Old 08-13-2019, 10:36 AM - Thread Starter
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HSU VTF-2 Power Supply Rebuild

Hello, This is my first post so I hope it gets to the correct HSU support group. If not, please help me direct it correctly. I understand HSU does not currently rebuild these models now, so I read previous threads about rebuilding the power supply. My unit's problem started with the traditional 60 cycle loud hum on power up and I was told that the power supply probably failed. After some research, I decided to replace all the electrolytic caps on the power supply board and did so. For reference, there are 10 electrolytic caps that were replaced. I powered up the sub woofer with no inputs connected and was happy to hear the 60 cycle hum completely disappear. When I connected the audio input, I saw the led signal lamp turn from red to green, indicating an audio input. However, no sound from the speakers. I tried both audio inputs, the RCA type low level input and the high level inputs from other speakers. Both inputs triggered the green led so I'm confident the sub woofer is getting an audio input. I'm now thinking something downstream is bad - perhaps either the final output transistors, Q1 / Q2 or their pre drivers Q6 /Q7. I'm not sure about those pre driver numbers. I don't see identification numbers on my board.



My questions are:
1) Is there an easy way via dvm to check these transistors in circuit, i.e., collector to ground? I can pull them if need be.

2) Does anyone have an up to date replacement list for these transistors? Some are available, others not.


I documented via photographs of the capacitor replacements if anyone would like to see that. I also have a list by capacitance and working voltage for these caps as well. Be happy to share that also. I really like this sub woofer and hate to lose it. I am aware of the Dayton Audio plate amp replacement and understand it's pretty much of a drop in replacement. But coming along so far on this rebuild, I don't want to throw in the towel yet. Thanks for any assistance you can give me. Bob
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post #2 of 3 Old 08-13-2019, 11:06 AM
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Maybe the mods will move this to https://www.avsforum.com/forum/113-s...ml#post9827558

I mention that thread because at least one Hsu employee visits it fairly regularly. Whether Hsu would be willing to give you the information needed for a DIY repair, I can't guess.

Alternately, have you contacted Hsu directly? I don't know what to expect, but they seem fairly accommodating.
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post #3 of 3 Old 08-13-2019, 01:37 PM - Thread Starter
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Hi Bob, Thanks for the reply. I checked the HSU support link you referenced and didn't see my thread there today. Not sure how to start a conversation at that link. I did contact HSU and got a note from Kevin re: the lytic cap replacements which was helpful. So far, I've not been able to locate a schematic for the power amp. I believe HSU bought these from a company and can't find their name right now. But, I just noticed a note from another user in this group by the name of Bernie7. Back on 4/30/2013 he did a cap replacement and later developed the no sound fault like mine. He said he traced the problem to the speaker relay circuit. Looks like HSU put this relay into the output speaker circuit to prevent thumping when powering up the system before sound is present. He said the relay (812H-1c) and two npn transistors (C945) were replaced and that solved the problem. Wow - wonder if I can be lucky and this solves my problem. Thanks again for your note and the push to get me to read my old notes.
Bob
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