burlyb
Active Member
In the past, I've done a "light restoration" on a couple of my Marantz receivers - caps, transistors, bias/dc - simple stuff like that. I have a slightly poorly taken care of 2220b that's been run 8 hours a day in my office for 5 years. It's had some repairs in the past, the FM drifts after a few hours and the volume is scratchy. I decided to freshen up the caps in the power supply and filter caps, regrease output transistors, reset dc offset and bias and basically clean it up a bit.
It's been a few years since I worked on my other amps and I did a bonehead thing and reversed a filter cap. Obviously it blew the main fuse and I discovered it and re-installed correctly. (I also subconsciously laid my soldering iron across a finger as penance). Piling on my bonehead mistake, I powered up with my dim bulb tester and it showed a dim bulb....but the bulb never dimmed out. I powered it up without anyway and blew the fuse. No smoke or pops. Face lamps lit up for a second, speaker protection relay never clicked and it went dark after about a second.
Now it powers up, but I've lost the right channel. I pulled all output transistors and they all check fine. Before I butchered this thing, it was always a bit touchy with the volume control. I cleaned it and other pots with contact cleaner, but still nothing. A tiny bit of static as I turn the volume up toward max. Mono works from both speakers. I went ahead and adjusted DC offset to 0mVDC and bias to 20mVDC on both channels using the correct pots (not per the service manual). They were quite a bit off.
Do I look at the controls further, did I cook the filter cap when reversed and/or should I look closer at the power amp board for other failures? I reversed a power supply cap on a previous receiver and it cooked a resistor, but this one showed no obvious displeasure. I'm beyond my analytical abilities.
Thanks.
Bryan
It's been a few years since I worked on my other amps and I did a bonehead thing and reversed a filter cap. Obviously it blew the main fuse and I discovered it and re-installed correctly. (I also subconsciously laid my soldering iron across a finger as penance). Piling on my bonehead mistake, I powered up with my dim bulb tester and it showed a dim bulb....but the bulb never dimmed out. I powered it up without anyway and blew the fuse. No smoke or pops. Face lamps lit up for a second, speaker protection relay never clicked and it went dark after about a second.
Now it powers up, but I've lost the right channel. I pulled all output transistors and they all check fine. Before I butchered this thing, it was always a bit touchy with the volume control. I cleaned it and other pots with contact cleaner, but still nothing. A tiny bit of static as I turn the volume up toward max. Mono works from both speakers. I went ahead and adjusted DC offset to 0mVDC and bias to 20mVDC on both channels using the correct pots (not per the service manual). They were quite a bit off.
Do I look at the controls further, did I cook the filter cap when reversed and/or should I look closer at the power amp board for other failures? I reversed a power supply cap on a previous receiver and it cooked a resistor, but this one showed no obvious displeasure. I'm beyond my analytical abilities.
Thanks.
Bryan
