WD Phono 3 - One channel only

[Richard Fensome]

Hi,

Firstly, can I please apologise for only re-appearing on this forum when I have a problem and need some help. Long story, which I wont bore you with, but I now finally have some time to try and sort out my neglected vinyl set up.

My WD Phono 3 is one channel only. I have swopped the valves to no effect. I have eliminated the turntable and the amp by swapping leads about and all the wiring looks OK.

Looking back on it now , I had started to notice a gradual degradation in the channel that has now given up the ghost. When the channel started to fail properly , I could kick it back into life by flicking the power on and off at the power supply, but a pause such as coming to the end of a side would be enough to send the channel back to sleep, as it were. Unfortunately, the channel has now flat lined and no amount of defibrillation gets it going again!

I really do not have a clue where to start and would greatly appreciate any advice as to how to identify the offending component.

Thank you in advance for your help.

Richard

[Richard]

Hi Richard,

Did you build it and can you check voltages as per the original build instructions? That would be my first check and will show if the valves and circuit are working. You can also easily compare the good channel readings with those from the the bad to confirm a fault.

[Richard Fensome]

Hi Richard.

Thanks for the reply.

I did build it, yes, and should have the instructions knocking about somewhere. I'll dig them and my multimeter out and see what I get.

i'll post the results if I may.

Thanks again

[Richard]

Originally Posted by Richard Fensome

i'll post the results if I may.

Definitely, that would pinpoint a circuit or valve problem. If they are fine it will indicate we're looking for a signal problem instead

[Richard Fensome]

Hi again,

Have finally had a chance to get the MM out and have run through the original post build checks again with some strange results:

Power capacitor 274v
Heater Voltages to ground, all three valves ~45V
Heater Voltages +ve to -ve, all three valves ~6.1V
HT Voltage Input Valves PIN6 Right 188.5V, Left 180.5V
HT Voltage Input Valves PIN1 Right 126-128V fluctuating, Left 124-126V
Cathode Voltages Output Valve, Pin8 129V, Pin3 127V
Cathode Voltages both input valves, pins 3 and 8. All ~1.0V ?????

Am I doing something silly on the final measurements? I am measuring at the pins to ground.

It is the left channel that is problematic btw.

Any ideas?

Thanks.

[Richard]

Hi, they're all pretty much spot on Richard inc the cathodes at 1V. The HT is a little high but is that perhaps because you don't have Pre3 plugged in to load the PSU? No matter anyway.

I'd look now to the signal input and output wires, plugs, sockets, resolder any suspect dry joints and follow the tracks of the pcb looking for shorts, wire strands, whiskers of solder, as a break or short on the signal seems to be the problem.

[Dik Dolan]

Does your phono3 have the round type stepup transformers? It might be worth checking one hasn't failed. http://www.world-designs.co.uk/forum...ead.php?t=4770

[Richard Fensome]

Good evening and thanks for the replies.

I was extremely confused as the instructions told me to look for ~120V at pins 3 and 8 of the input valves and i was a little bit out on both channels! Nice to know i wasn't being that silly!

Now for the confession.......

I decided to go down the MC route about a year ago and added some ebay sourced mic transformers with a 20x gain - sounded surprisingly good considering the price but definitely not OEM.

What's the best way to test these as the input wiring looks sound? Can I measure the output voltages with a signal going through them to see if one has failed or is resistance a better test - or is it best just to switch output wires between channel inputs on the PCB?

Cheers,

Richard

[Richard]

Originally Posted by Richard Fensome

Good evening and thanks for the replies.

I was extremely confused as the instructions told me to look for ~120V at pins 3 and 8 of the input valves and i was a little bit out on both channels! Nice to know i wasn't being that silly!

Hi, mine says,

"Check the Cathode voltage on pin 8 and pin 3 of the output valve (junction with R23/R24). It should read about 110v DC.
Check the Cathode voltage on pin 8 and pin 3 of the input valves (R7/R8 and R17/R18). It should read about 1v DC."

which agrees with the circuit so you're fine.

Back to checking the signal path or indeed those TXs maybe