Hlly T-Amp 90 Power Supply Failure

[paulflowe]

Hi - I switched on one of my T-Amp 90s a couple of days ago and it no longer powers up. I have taken the case off and cannot see anything untoward (no blown caps etc.) The huge toroid in the middle smells a bit but not too strong.

Any ideas as to what could be wrong please? I am not a big DIY'er so don't have the skills to diagnose the fault myself, though the smelly toroid could be a suspect. I have a couple of other T-Amp 90s which remain fine, so if I can't fix this fault would anyone with more diagnostics expertise be interested in buying it 'as is'?

Thanks to all and 'Happy Easter!'

[Ali Tait]

How much would you want for it?

[4season]

First, see if HLLY offers any sort of warranty.

I doubt that the power transformer is smoked; at least I hope it's not, because it's the single most expensive part in that amp! Far more likely that the two 10000 microfarad capacitors have failed, causing the fuse to blow. Don't replace the fuse until you have corrected the underlying problem.

[paulflowe]

Hi - it was 2nd hand so I doubt there's any warranty. I'll open the unit again and check those items. I guess it's worth a try before I look to sell 'as is'. I'll drop another note here once I've done that.

Thanks for now.

[paulflowe]

Hi all - I have opened up the case and cannot see any obvious problems. I am able to e-mail some pics to anyone who may be able to diagnose that way. The unit simply won't power up.

[mfong]

I suspect it went into "fault". There's a protective circuit in the chip itself that shuts the amp down when it sees too high a voltage.
Hlly runs a transformer that's pretty much at the limit of the range of the chip +- 35 volts.
If your AC voltage is running at 120 volts (for US), a lot of newer mains are at 120 instead of the more traditional 110. The margin of error that you get with household voltage can shut the amp down (in the long haul a good thing because it's protecting the amp, but a pain).

I noticed that the 41hz folk working with the chip mentioned staying at +- 24 to avoid the problem. It's also discussed some in the technical references for the TA 2022 chip where they talk about putting a relay between the amp and your speakers (not sure what that has to do with over voltage on the input end though). I suspect that Hlly kept the input voltage on the high side to let them sell the amp as 90 watts/channel.

It's not that big a problem to fix. You just unplug the amp, wait a while (until your line slips back to normal) and it should power up normally again. It's not a lot of fun though and the first couple times I thought I'd done something terrible to the amp. A voltage stabilizer will also fix the issue for the long term, but my issue is why should you buy a hundred dollar voltage stabilizer to keep a 200 dollar amp working.

[Ali Tait]

A cheaper alternative would be a variac from ebay.

[paulflowe]

Hi all - first, thanks for the replies. Second, I've just powered it back up after removing the fuse to check it hadn't blown (it hadn't) and replacing it. It fired up first time! I will have to keep an eye on this in case it happens again. As I said, this unit was a second hand one so I do suspect an underlying fault. I have two other units so these are fine for my AV use, and may well look to sell this unit "as is" at some point.

[mfong]

Just to be clear, are you saying that you have two other t-90's that don't do this or that have never done this?

[4season]

Originally Posted by mfong

Hlly runs a transformer that's pretty much at the limit of the range of the chip +- 35 volts.

Ouch I can't believe I missed that one! I think I get what you're driving at, and I agree. There's no cost-effective remedy here I'm afraid.