Carver MXR-2000/receiver 2000 with left phono channel out.
- Thread starter Dutch54
- Start date
You'll need a signal generator and oscilloscope, both ideally 2 channels. If you don't have them, perhaps you can input a signal to the phono jacks using a computer or smart phone based app, and do comparison testing between channels with the VAC function of your DMM.
Alternatively you could just use resistance testing and hope to find it. I assume the phono jacks share the same ground. So ground your ohm meter lead.
Since it's stereo, each component in the channel path is the same up to what's probably a dual opamp in a single package, and again the same up to the selector switch.
Now, check resistance from ground to the first component in each signal chain, they should be "comparable". You'll see some variation, but it should be close between the same points in each channel.
If everything checks out to the selector switch, try checking after the switch, but it'll probably then get very complicated due to all the additional switches and features.
The opamp. Down load the data sheet for it and test for correct VDC on its supply pins. Very important to do this.
Without a signal input and scope I don't know how to test if it's good. But if it's socketed, you may be able to swap it with another and see if it's blown.
On my PL2000 preamps, it's all caps, resistors, and one opamp, to the selector switch. And that opamp runs off lower voltage rails then the others due to phono being a lower level source. If B+ and B- rail voltage is too low for the phono opamp to work, no phono, but the other modes like FM would still work as they get a higher voltage.
So also ensure your power supply and distribution is spot on. Matter of fact, always check the power supply output and rail voltages first. It should have 3 rails, B+, B-, and ground if it has a center tap transformer, like I think it does.
Hope this helps.
Alternatively you could just use resistance testing and hope to find it. I assume the phono jacks share the same ground. So ground your ohm meter lead.
Since it's stereo, each component in the channel path is the same up to what's probably a dual opamp in a single package, and again the same up to the selector switch.
Now, check resistance from ground to the first component in each signal chain, they should be "comparable". You'll see some variation, but it should be close between the same points in each channel.
If everything checks out to the selector switch, try checking after the switch, but it'll probably then get very complicated due to all the additional switches and features.
The opamp. Down load the data sheet for it and test for correct VDC on its supply pins. Very important to do this.
Without a signal input and scope I don't know how to test if it's good. But if it's socketed, you may be able to swap it with another and see if it's blown.
On my PL2000 preamps, it's all caps, resistors, and one opamp, to the selector switch. And that opamp runs off lower voltage rails then the others due to phono being a lower level source. If B+ and B- rail voltage is too low for the phono opamp to work, no phono, but the other modes like FM would still work as they get a higher voltage.
So also ensure your power supply and distribution is spot on. Matter of fact, always check the power supply output and rail voltages first. It should have 3 rails, B+, B-, and ground if it has a center tap transformer, like I think it does.
Hope this helps.
I would do as George said. Comparative readings can help a great deal. Also check for correct BE and BC readings on Q402 and 404 using the diode test portion on a DVM with unit unplugged. I would also compare scope readings on the output pins of the opamps and the input pins on IC 404. I've had the NJM and TC series chips go bad in various brands over the years.
As a side note I recently had a PL preamp come in that had bad left channels in both MM and MC circuits. It used separate chips. Replaced both chips and all was good.
As a side note I recently had a PL preamp come in that had bad left channels in both MM and MC circuits. It used separate chips. Replaced both chips and all was good.
You did not mention if you have the Service Manual or not. I will send you mine.
There is a lot going on in that receiver. George and DSM gave you some good info. I will add that you can eliminate 99% of the circuitry because you said everything except the Left Phono channel is good (I like to deal with the positive). Most likely you have a mechanical issue - bad RCA Jack, bad RY 501 relay, bad MC/MM switch, cracked solder run, cold solder joint, etc. Do you have any signal from the Left Channel in your headphones? Can you plug in another amplifier into your Preamp Out Jack (you have to remove the buss bar first), if you have no audio there; then your problem is likely in the Phono section or the related controls. Wiggle or rotate all the controls before you do anything.
To isolate the issue, find where you have a good signal (could be the Left Phono Input on the RCA Jack), then go HALFWAY through the Phono section (maybe to the Preamp Output) because you know there is no output there. Then go back HALFWAY again (maybe where it goes off the Input Board and over to the Tone Board). Keep doing this with a known good signal (like a LP playing some Led Zeppelin) and watch out for the tracks between the songs. Compare Left to Right in the same area and you will be very close when the signals become different.
Remember that signal resistors are very reliable. Capacitors can short, diodes and transistors can go open circuit, and wires/leads/solder can break leaving you with no signal.
There is a lot going on in that receiver. George and DSM gave you some good info. I will add that you can eliminate 99% of the circuitry because you said everything except the Left Phono channel is good (I like to deal with the positive). Most likely you have a mechanical issue - bad RCA Jack, bad RY 501 relay, bad MC/MM switch, cracked solder run, cold solder joint, etc. Do you have any signal from the Left Channel in your headphones? Can you plug in another amplifier into your Preamp Out Jack (you have to remove the buss bar first), if you have no audio there; then your problem is likely in the Phono section or the related controls. Wiggle or rotate all the controls before you do anything.
To isolate the issue, find where you have a good signal (could be the Left Phono Input on the RCA Jack), then go HALFWAY through the Phono section (maybe to the Preamp Output) because you know there is no output there. Then go back HALFWAY again (maybe where it goes off the Input Board and over to the Tone Board). Keep doing this with a known good signal (like a LP playing some Led Zeppelin) and watch out for the tracks between the songs. Compare Left to Right in the same area and you will be very close when the signals become different.
Remember that signal resistors are very reliable. Capacitors can short, diodes and transistors can go open circuit, and wires/leads/solder can break leaving you with no signal.
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You may have found the issue. That Sonic Hologram Switch is likely in need of a good cleaning. Many switches on the Carver amps sit in one position for years, moving it can create all sorts of issues.
Balance - if it is not far off, that is pretty common. If it is far off, same story; likely a dirty potentiometer.
I would invest is some high quality electronics cleaning spray such as DeoxIT or something from CRC or MG Chemicals. Some of the sprays have lubricant. You just need a cleaner right now, lubrication can be a follow-up. If the spray cleaners don't solve the issue, and you know it is a particular switch or potentiometer; you may have to replace it. Some can be rebuilt, but that is a job for an experienced technician.
Balance - if it is not far off, that is pretty common. If it is far off, same story; likely a dirty potentiometer.
I would invest is some high quality electronics cleaning spray such as DeoxIT or something from CRC or MG Chemicals. Some of the sprays have lubricant. You just need a cleaner right now, lubrication can be a follow-up. If the spray cleaners don't solve the issue, and you know it is a particular switch or potentiometer; you may have to replace it. Some can be rebuilt, but that is a job for an experienced technician.
Last week I had a Harman Kardon HK385i come in that had a nearly dead phono section. Had to clean the phono select switch twice over a 2 day period to get sound back in. Becoming very common for me in the last 5 to 10 years to have switches with a lot of tarnish build up from units sitting unused. On older products I find it best to clean all switches and controls early on.
Before and after servicing a PL2000S2 preamp CTS branded balance pot. Look at the deposits on the silver plated wiper slip rings. This had been cleaned with DeoxIT spray several times beforehand with unsatisfactory results.
A nylon rotary Dremel brush, nor a brass rotary brush would not polish the deposits off the slip ring and contacts. It required careful use of a well worn steel rotary brush.
All parts were then cleaned in alcohol and carefully greased with DeoxIT grease before reassembly.
Actually rather surprising the deposits I've found on wiper slip rings and the contacts in old pots.
Keep the parts in perfect order if you do this as the carbon tracks may be logarithmic and must be reassembled correctly in order.
A nylon rotary Dremel brush, nor a brass rotary brush would not polish the deposits off the slip ring and contacts. It required careful use of a well worn steel rotary brush.
All parts were then cleaned in alcohol and carefully greased with DeoxIT grease before reassembly.
Actually rather surprising the deposits I've found on wiper slip rings and the contacts in old pots.
Keep the parts in perfect order if you do this as the carbon tracks may be logarithmic and must be reassembled correctly in order.
