Conrad Johnson PV7 preamp dead
- Thread starter naderpe
- Start date
CJ PV-7 rectifier
It's a BR805D rectifier used in the filament and turn on delay power supply. Rated at 50 volts and 2 amps. If you can't find a schematic, send me a PM with your email address & I'll send you one that is nearly impossible to read but that's all I have.
Ron
It's a BR805D rectifier used in the filament and turn on delay power supply. Rated at 50 volts and 2 amps. If you can't find a schematic, send me a PM with your email address & I'll send you one that is nearly impossible to read but that's all I have.
Ron
yesterdaze
Member
Hi Ron, I replaced the original Bridge Rectifier with a beefier Sylvania ECG169 - 2 amps and 600 volts. The preamp worked for more than a month and then the left and right channels began to distort a bit and fail. The only way I can get both channels to work is to lightly tap the board near the relay, or to manually actuate the relay myself. I don't think the new Sylvania Bridge Rectifier failed, do you? The correct current seems to be available everywhere else, and this is evident when I manually actuate the relay.. Why would there not seem to be enough voltage/current to the relay coil?
billyz
Super Member
Try resoldering the relay and clean the relay contacts . I have used 600 or 1000 grit sandpaper soaked in deoxit. Pull thru the closed contacts a couple times .
yesterdaze
Member
Already resold red last week. I was a little careless with the deoxit. Sprayed direct to the contacts yesterday. Applied compressed are to remove excess, and that made my problem worse. It was then that I discovered the relay would not work. I think I soaked and shorted the relay coil which might explain why there is less than one volt going to the relay.maybe it will dry out in a week???
Do you have a part # for the relay?
Or can you read any of the specs.
If we can't find an exact replacement, we likely can find a suitable work around.
Also deoxit does dry . Once blown out, if you give it a day or so, it might come back to life.
Or can you read any of the specs.
If we can't find an exact replacement, we likely can find a suitable work around.
Also deoxit does dry . Once blown out, if you give it a day or so, it might come back to life.
billyz
Super Member
One Volt does not sound right to me. you may have a supply problem to the relay. I would look for a diode and a voltage regulator and or transistor in the power circuit to the regulator. on the PV8 the relay voltage is part of the filament circuit, so I imagine 6 or 12 volts should be present. Possibly your relay has some markings on it as well, maybe its a 5 volt relay.
I don't have the schematic of PV7, this is PV10 and see whether it's the same circuit.
You need to check the input of the SCR to make sure you have drive from Q4. 1V across the coil can mean you don't have drive. I won't be to hasty in doing something about the relay, they are usually harder to replace, but the Q4 and Q6 are dime a dozen.
yesterdaze
Member
Thanks. I do have a part number and source for the relay. I may buy it this weekend
yesterdaze
Member
Thanks. My relay coil says 12 volt dc. I suspect that the 12 volt supply will appear once I remove and replace the defective relay.
I'm with Alan on this.
Unless the coil is shorted you should be seeing about 12v at the 2 coil leads
There are only a couple of components in the coil circuit. You should test.
It's possible you had a relay contact issue which during deoxit treatment somehow caused an issue upstream
Unless the coil is shorted you should be seeing about 12v at the 2 coil leads
There are only a couple of components in the coil circuit. You should test.
It's possible you had a relay contact issue which during deoxit treatment somehow caused an issue upstream
arts
Addicted Member
The most common problem with the relay timer circuit used in CJ preamps is the timing capacitor. Over time,age-related leakage increases to the point that the capacitor can never build up a charge sufficient to actuate the driver circuit.
Replace C11 (47uf/35v) and verify the value of R9,which should be 910K.
Also,as many control cleaners are conductive until completely dry,this could also prevent charging.
Replace C11 (47uf/35v) and verify the value of R9,which should be 910K.
Also,as many control cleaners are conductive until completely dry,this could also prevent charging.
yesterdaze
Member
I agree that the bridge seems to be alright. The problem may be upstream as suggested by NJ Phoenix and you. I will start with the capacitor and replace R9. Thanks guys.
yesterdaze
Member
Replaced C11 with (47uf/50v) and R9,which was 910K, The original parts were not out of specifications. Once the new components were installed, there was no change. Before I replace the relay, I want to replace the diode. The diode next to the relay seems to be out of specifications - D5? 1N4148. Without removing it from the PC board it is giving me unusual impedance readings on my multi tester - inconsistent with the several other diodes of same size and colors. I may have to buy some diodes. I have a few questions as to replacing the suspicious diode:
- Obviously these are directional/polarized, so the black end of the diode indicates the direction, correct? Black end is in or out?
- These appear to be color coded, similarly to the resistors?
- I found a few new diodes in a box, and intend to use that is a bit larger, but similar in color. I have 1N4003, 1N5231B, and 1N4759A. Are any of these a compatible value, or am I asking for trouble?
The diode across the relay will not read right, it will read very low resistance because the relay coil is across the diode, you are measuring the resistance of the relay coil, not the diode.
You can try 1N4003, but I not sure the diode is your problem. I would pull one side of the diode out and measure the resistance of the diode IN BOTH DIRECTION to determine whether the diode is shorted. I doubt it.
You can try 1N4003, but I not sure the diode is your problem. I would pull one side of the diode out and measure the resistance of the diode IN BOTH DIRECTION to determine whether the diode is shorted. I doubt it.
MichaelXX2
New Member
I've developed a similar problem with my PV7. The amp just simply won't respond at all when I turn it on. By accident I shorted the negative and middle terminal on the BR805D rectifier with my multimeter, and the red light on the front panel turned on, and the tubes all started warming up. I didn't want to leave it shorted for too long, but does that indicate that all I need to do is solder a new rectifier in there?
