I need some help guys.
One of my Zen mono amps [SE84C] stopped working last night.
All tubes glowing, no sound.
Problem is defenately the amp; switched amps, switched cables etc. to locate the problem.
Opened it up but nothing to see there what could cause it.
HOW TO CONTINUE?
HELP!

Nico

Lighting up, but no sound coming out sounds like the input tube or related circuit is having an issue, or the volume pot possibly. Try swapping the input tube, try flicking the bias switch a few times, try cranking the volume knob left right a few times and see if it comes back. That will hopefully help you narrow down the fault.

I had a similar issue last week on bridged Rachaels. Took some hunting down to find a signal tube on the phono amp had just eased out a shade.

Nico,
To recap, you own 2 mono amps, 1 of which is not working. The one not working has tubes glowing, so you know it is getting power. You have checked cables and tubes, finding no fault with them. There is one more thing to consider. The RCA input jack may have problem. You can take the cover off and pull on the wires going to the jack. These wires can be physically stressed when pulling off a tight interconnect cable, ESPECIALLY if the interconnect was being twisted trying to pull it off.

4krow wrote on 05/28/14 at 18:53:59:

Good call. The interconnect itself could have a problem as well unless that has been eliminated as a problem.

What chassis mount RCA do you like over stock?

Cool! Tell me how they fair.

Also looking for better power inlet for my Decware amps - Steve isn't happy with them either, so I've been keeping an eye out for a good IEC inlet with solid connectivity, that actually fits a standard IEC plug!

This suggestion is only half serious....

you know how you can install some appliances, like dishwashers, by direct wiring to the box, or wiring a pigtail to the box and plugging it in?  To eliminate weakness at iec contacts, you could hardwired a cord/plug (a nice one) into your amp (haven't thought about aesthetics or where it could come out, etc).  It's one way of avoiding the problem entirely. No connector would have a better electrical connection.  Would have to remember to handle the fuse.  And you save having to buy a female iec plug if making your own cords.

Again, only half serious, but it seems like one of those "old way, better way" kind of situations.

you're right.

Nico, So far:
you have opened the amp.
you are comfortable with electronics
you have switched in known good tubes
you have switched in known good cords and cables


... if you suspect the IC connections...  
you can with the amp open and on, (be careful!) probe the wires at the RCA inputs with some wires carrying music signal.  this will tell if your rca jack is somehow busted or bad contact.

if you suspect the volume pot(s)... it's just a resistor, you can short it with a piece of wire and that will provide instant "full volume".  that'll tell you if the pot is broken.

personally I don't know enough about the lines going to the tubes and which are high voltage... so that's where my troubleshooting would end. (I guess with NO POWER, visually inspect for loose wires on tube sockets.) otherwise  send home to Peoria.

Anyway, only do the above (plug in and operate a opened amp) if you know how not to kill yourself from high voltage.

THANKS guys for your help.
Can you believe I had a bad night because of this..?
Listening to music is like a daily medicine for me against stress.
So today I decided to open both [mono bridged] amps, lay them on one side with tubes inserted and powered them up.

Taking my DMM, I started measuring the voltage across different points inside the working amp, and then in the defective one.
Soon I measured no voltage after the 1K resistor that feeds the OT's....
After shutting everything down I de-soldered that resistor and YES SIR, it is "open" .

That means the OT's did not get any power and that means tubes glowing but no sound.
So I stumbled upon the answer this way!

I asked a local tech and he confirmed that the bad resistor would indeed cause the problem I described.

As seen on the later schematics, this resistor has been upgraded by Steve from 1K10w  to 1K50w. Maybe the 10w version prooved to be thermally stressed too much, I don't know.

What I do know is that tomorrow I'll be buying two 1K50w resistors, solder them in place and hope to get my daily dose of medicine again.

For all who own a older Zen; replace the resistor for a 50w version.
Nico

Very good sir! I am pleased that you were able to find this problem./

Way to go Nico. It has been fun to watch the progress.

As to the side thread topic...loose IECs, I personally would not hardwire a cable since I find cable rolling very useful, especially with a new component introduced in the blend. I did make and buy cables with quality, but also diversity in mind though. All my nice PCs sound good but different, and depending on what they are plugged into, sometimes for inexplicable reasons, one will really match a component within the synergy of the whole. For example, I have a 10 AWG PI Audio cable I got while in development. It has Gold Furutech ends, and a really good damping and noise reduction design. It sounds (or doesn't sound) really good everywhere, transparent, dynamic and quiet, but in my DAC it is awesome. These strange synergistic things can be sort of shocking for me.

BUT LOOSE IECS.....until you find the right replacement, wrapping the Power Cord IEC connector with teflon tape until it fits snuggly will stabilize it in a dampened sort of way.