KilgoreCemetery
- Apr 12, 2017
- 258
- Joined
- Apr 12, 2017
- Messages
- 258
Everything on this receiver seems to work fine except when you hook up a load to the speaker connects. I just finished recapping and replacing a couple of bjt's in the FM section and finally hooked it up to some speakers so I could start enjoying it, but the music sounds horrible. It's not just FM either. Phono, AM, Aux.. doesn't matter. It's all garbled. I could have swore that I listened to it before doing all that work and it sounded fine, so I put it back up on the bench and plugged in a pair of headphones... and it sounds very clear.
After doing some testing, I realized I can turn the distortion on and off in the headphones by pushing the button that enables the speakers. It doesn't matter if it's a real pair of speakers or a pair of dummy resistors, nor does it matter if it's "A Speakers" or "B Speakers". I finally circumvented the speaker buttons and jumpered some wires from a small speaker directly to the output on the main amp circuit board and it distorted the sound in that channel. As soon as I pulled the jumpers back off, the audio cleared up in the headphones.
It doesn't go the other way around either; disconnecting the headphones has no affect on the quality of the sound coming from the speakers. It seems like the distortion is only present when there is a load. I'm using a pair of Pioneer CS-63DX speakers (8 ohms) or a pair of 8 ohm dummy load resistors depending on where the receiver is sitting. 8 ohm speakers are what this receiver is rated for.
From there, I tried to adjust the trim pots according to the service manual, but step 1 under Audio Adjustments doesn't work. I'm supposed to be probing both sides of a resistor and adjusting a variable resistor until I get 7.5mV, but no matter how far I turn it in either direction, I get 0.1mV. This goes for both channels. They are 0.5 Ohm resistors and when I test them, they're spot on. I also sprayed the VR with some Deoxit and checked it for resistance. It goes up and down as I turn the center, just as I would have expected from a working unit.
I really feel like I'm missing something silly, but I have no idea what. Does anyone have any ideas of things I could try?
After doing some testing, I realized I can turn the distortion on and off in the headphones by pushing the button that enables the speakers. It doesn't matter if it's a real pair of speakers or a pair of dummy resistors, nor does it matter if it's "A Speakers" or "B Speakers". I finally circumvented the speaker buttons and jumpered some wires from a small speaker directly to the output on the main amp circuit board and it distorted the sound in that channel. As soon as I pulled the jumpers back off, the audio cleared up in the headphones.
It doesn't go the other way around either; disconnecting the headphones has no affect on the quality of the sound coming from the speakers. It seems like the distortion is only present when there is a load. I'm using a pair of Pioneer CS-63DX speakers (8 ohms) or a pair of 8 ohm dummy load resistors depending on where the receiver is sitting. 8 ohm speakers are what this receiver is rated for.
From there, I tried to adjust the trim pots according to the service manual, but step 1 under Audio Adjustments doesn't work. I'm supposed to be probing both sides of a resistor and adjusting a variable resistor until I get 7.5mV, but no matter how far I turn it in either direction, I get 0.1mV. This goes for both channels. They are 0.5 Ohm resistors and when I test them, they're spot on. I also sprayed the VR with some Deoxit and checked it for resistance. It goes up and down as I turn the center, just as I would have expected from a working unit.
I really feel like I'm missing something silly, but I have no idea what. Does anyone have any ideas of things I could try?