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-   -   I have power but no sound??? (http://www.diyaudio.com/forums/tubes-valves/220894-i-have-power-but-no-sound.html)

just an idea 3rd October 2012 02:14 PM

I have power but no sound???
 
Hi,
I have a little hybrid valve amp I picked up in taiwan, for the price the sound it produces is (was) surprisingly good. Unfortunatley it's now not working and I want to get it going again.
I think the cause may of been a power surge in a storm... but it may not be... the main reason I think this is my DVD player broke at the same time, I have a really cheap multiplug adapter that claimed to have surge protection.... I live and bought it in thailand so this may not be true and we have big electrical storms here.
Anyway,
The amp will power up, lights come on, the digital input display comes on but no sound comes out... I know it's not the speakers or cables at fault. What are the most likely problems?
Thanks

Rundmaus 3rd October 2012 02:57 PM

This is very difficult to answer without more detailed information.

Can you provide a schematic for the amp? Pictures (especially with the cover taken off) may be helpful too...

Do the valve heaters come on when you apply power?

Andreas

PS. Your thread title is a common problem of many bands - they have power, but no sound :D

just an idea 4th October 2012 02:49 PM

yes the valve heaters come on, until you actually try to play music it seems like everything works and comes on as normal....

I have no schematic and the manufacturer wont send one, I think so people can't copy the design... although it's nothing extra special. I'll take some picture and post them once I'm done.

just an idea 4th October 2012 03:12 PM

2 Attachment(s)
One photo of the outside so you have an idea of the style of amp, then the inside. I've pulled the usb circuit out the way... so you can see more, but I think you'd have to be a genius to figure out the problem from the photo.... I have a multi meter if you can in very simple language describe for me where to poke the spikes and what values I would expect.

azazello 4th October 2012 03:52 PM

What kind are Your tubes? After el. storm tubes must be alive.

tauro0221 4th October 2012 04:31 PM

Hi,
From the picture that showed the board I can see the pins for the tubes. Check to see if you have high voltages. You have to get the tube pins so you can check the voltage for the plate and grids. Also try to see if you can locate a fuses around the power supply. I know it is hard to troubleshoot without a schematic but you need to see if you can figure out where it is everything.

kevinkr 4th October 2012 06:25 PM

This thing has a micro-controller in it, when you select other sources does it indicate that it switched to them?
Do the relays click when you select a (different source?) I can see the volume control is a pot.

Can you ship it back to the manufacturer for repair?

Since you are inexperienced please be aware that there may be moderately high voltages internally in addition to your hazardous 220V mains. Please read the safety thread here before poking around inside.

speakerfritz 4th October 2012 08:27 PM

look for a b+ voltage fuse. Also, get someone to check your bias. sometimes you can have lit filiments but if the bias does not show current you could have a blown b+ fuse, or blown resisters, worse case....a blown transfomer. the filments are on different windings from the B+.

just an idea 5th October 2012 04:49 AM

the main fuse (actually only one i can find) was blown but I replaced it and now when I turn it on it doesn't blow again.

The Inputs change as normal as I flick through them with a healthy 'click', so that all working.

The Valves are 6N2's... I think but may be wrong are similar to 12AX7.

Sending it to the manufacturer will be my last option as I'm likely to get stung by import duty as it come back Taiwan to Thailand.

What's a b+ voltage fuse and where do I find it.... I'm keen to learn, at the moment all I know is I don't like electric shocks and will be very careful to ensure I don't get one.

M Gregg 5th October 2012 08:11 AM

Hi,

I would forget the tubes, It looks like the power amp section could be a Chip amp (is this two IC's one for each channel on the large heat sink?)
Could be voltage regs?

If you have a multi-meter and use some cheap (car speakers) see if you get a hum (BUZZ) from the output if you connect a meter lead to the volume control connections. If the amp is in two stages tube preamp and chip output. You need to see if the chip output is working. If it has two chips one each for left and right
If they both don't work it could be a common PSU fault. If its a common stereo amp then this is a starting point<<<check to see if you have power rails and can you get a BUZZ if you connect a meter lead to the input..Can you hear a hiss from the speakers?

Its hard to give advise without a schematic..and be careful of high voltages!

Work from the output section to the input..ie if the power amp is faulty you can forget the rest!

So the trick is to find out where or what is the power amp..get this working first!

Regards
M. Gregg


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