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Help! Conrad Johnson PV2 relay not working

190.105.52.152
Posted on November 22, 2015 at 22:33:15
pastito
Audiophile

Posts: 535
Joined: June 8, 2001
 Hi folks!

A friend of mine brought me a Conrad Johnson PV2 preamp that is having HV relay blues.

I checked and the timer circuit seems to be pretty simple. There is a 220 uF cap that gets filled slowly and then there are two NPN transistors in darlington configuration. The first one is 2N3904 and the second one is a MJE182. The relay is a double inversor - two pole with a 12VDC coil. I removed the relay and tested it with a 12VDC power supply and it works perfectly.

I measured voltaje across the relay's diode and it nicely ramps up until it hits 6.82 volts and then it stays there... and that is not enough juice to fire the relay.

Where do you think the problem lies? Should I replace the cap only?
The 2 switching transistors? All of the above?

This pre amp is built like a tank, but PCB access is impossible from above to measure voltages... and I find it way too dangerous to turn it on dissassembled... I am afraid I cannot measure the voltage feeding this very simple but seemingly effective timer.

What you you think I should do?


Regards
PS. Sometimes it works... and the preamp sounds very nice indeed.

 

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RE: Help! Conrad Johnson PV2 relay not working, posted on November 22, 2015 at 22:38:11
unclestu
Dealer

Posts: 5851
Joined: April 13, 2010
 RElay not working usually mean the electrolytic cap is leaking. Change it out.

 

RE: Help! Conrad Johnson PV2 relay not working, posted on November 23, 2015 at 05:35:17
Alpha Al
Industry Professional

Posts: 2958
Location: N. Carolina
Joined: February 16, 2004
Contributor
  Since: December 3, 2015
 It's not a HV delaying relay. (at least in my PV2A). It's there to short the outputs,stopping thumps at turnon and turnoff.

Mine was not closing all the way, allowing turnon and turnoff noises to pass. The solution was to remove the plastic cover (very carefully) and burnish the contacts with a burnishing tool.

It sounds like your timing capacitor is bad. I doubt that the transistors are bad.

 

RE: Help! Conrad Johnson PV2 relay not working, posted on November 24, 2015 at 07:14:23
pastito
Audiophile

Posts: 535
Joined: June 8, 2001
 Changing the capacitor did not help. I get the same voltage. I measured and the power supply is providing 13 volts to the circuit.

My best guess is that it is one of the transistors. As resistors and zener diodes are OK.

Any thoughts?

 

Almost solved, posted on November 24, 2015 at 18:25:05
pastito
Audiophile

Posts: 535
Joined: June 8, 2001
I changed both transistors... it now works consistently due to the higher gain of the transistors but still output voltage is too low (about 8 volts).

I see that there is a big power supply cap that leaked some juice. It is a Mallory 40uF x 400 volts.

I am 99% sure that is the main problem. I will replace it ASAP.

Thanks you all

 

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