B1 has died

[KatieandDad]

Ooooo- what is THAT cool toy you have there?!? I think I might want one

It's an E-Bay gadget, a very handy toy.

http://www.ebay.co.uk/itm/128-64-LC...744801?hash=item1a0e2969e1:g:rGUAAOSw-zxWndes

 

[KatieandDad]

I've got no idea what could be wrong now.

 

[KatieandDad]

This is getting bizzare.

All four NFETs test correct but have been replaced as a matter of course. 4x 9v1 back to back diodes have been installed across the pot wiper and 0V.

There is still no output from either channel.

D2 - the LED - illuminates indicating power to the board.

 

[Rodeodave]

You still haven't posted pics of the pcb in question. Let's see those solder joints.

 

[KatieandDad]

I'll post some photos later, the soldering is not the issue.

 

[jean-paul]

Does it have a muting relay (with a broken driver transistor) ?

 

[propitious]

This might be too basic, but sometimes starting over with the basics is best by using a scope (or get a cheap USB one if you don't have one), put a signal on the input, and put the probe at each stage one at a time to see where you lose the signal exactly. If needed you can check dc voltages with the probe at each lobe also, to see if you are losing voltage where there should be some. Then tell us what you find.

 

[jean-paul]

If the JFETs are OK and the PSU is working we have to think of basic problems

I can not imagine coupling capacitors to be both defective. Otherwise i can think of a defective source selector or potentiometer. Would be strange to see two channels defective at the same time.

Jfets are a little more resistant than Mosfets, but you can still take them
out. All the cases I have seen have to do with Tube sources, usually
the turn on/off transient of somebody's tube preamp.

Still some designers of tube stuff omit muting relays with delayed turn-on and instant turn-off. Also on this forum, one has a hard time convincing such designers of the benefits as they mostly concentrate on their own situation which does not ask for such protection. I wish we could make this item a standard thing on any analog source/buffer/preamp.

 

[billshurv]

LED coming on does not guarantee power to the circuit. Most likely reasons for no sound are

1. Power to board from PSU broken (10 seconds to check with DVM)
2. Output ground broken somewhere

I can't think of anything else that would cause a loss of both channels. If those check out then next step is CDP into B1.

 

[KatieandDad]

I agree, the weather is too cold to get out the silly scope and the sig gen at the moment.

 

[KatieandDad]

Oh I feel such a fool.

The problem with a lot of DIY equipment is that the Inputs and the Outputs are often not marked. I was relying on memory - DOHH !!!!!

When I got the Fluke out I realised that the amp had been connected to one of the inputs and not the output.

 

[vdi_nenna]

All's well that ends well.

I rebuilt a channel of a F5T think it was out.
Turns out it was an active crossover pot.

It happens.

Vince

 

[KatieandDad]

I've left the BTB zeners in the B1, just in case something does decide to try and take it out. I've now got a set of 4 x NFETs as spares too.

 

[jean-paul]

Building a class D power amp will do as punishment.

 

[KatieandDad]

No way. I'm more than happy with my Aleph 4. 100W of pure Class A for me.

 

[Nelson Pass]

When I got the Fluke out I realised that the amp had been connected to one of the inputs and not the output.

Yes, I've done that.

 

[AndrewT]

Oh I feel such a fool.

The problem with a lot of DIY equipment is that the Inputs and the Outputs are often not marked. I was relying on memory - DOHH !!!!!

When I got the Fluke out I realised that the amp had been connected to one of the inputs and not the output.

You could change all your RCA/Phono to XLR.
The outputs and inputs are deliberately male and female so one cannot mix them up.

 

[Eric]

I've done this one, too. No matter how hard I tried (and I was probably a bit over zealous with my signal generator), I just couldn't drive those jFets backwards.