If you’re looking for a repair for this particular model of receiver, sorry – Rain City Audio no longer takes Yamaha CR series for repairs due to them requiring such an extreme amount of work. This post is a good resource for techs, though, so it’s still up.
The Yamaha CR-2020 drives 120W/channel into an 8 ohm load and supports 3 pairs of speakers (but only plays 1 or 2 pairs a time), dual phono inputs supporting both moving magnet (MM) and moving coil (MC) pick-ups, tape-copy functionality with a separate output selector, and a variety of tone control and FM Stereo adjustments.
The owner reported the unit was playing, then suddenly went silent and wouldn’t play anymore. Telltale signs of smoke rising from the inside can be seen on the vent slats.
Let’s take a look inside…
An absolutely mammoth transformer, and the two final amplifier modules with enormous heat-sinks. Above the transformer is the power supply section; the far left moving out of the photo is the tuner.
The power supply has had three capacitors replaced but most are original. The lights have been modified at some point as well, although somewhat sloppily.
Yamaha used a drive-shaft type arrangement for the MM/MC switch with two flexible linkages to turn a switch all the way at the rear of the unit from the front panel. The dial arrangement is one long string that wraps around about a half-dozen pulleys. Not only is this a very complex, powerful electrical design it has a lot of physical components as well.
Overall, there’s a lot going on under the hood. It’s time to investigate further.
Here’s a previous repair with a sloppy solder joint visible.
Old and new caps:
It’s generally not recommended to leave old caps in place if some have failed…the others are the same and experienced the conditions, they’re going to go eventually – which is what landed this one back in the shop.
On the underside, the board was badly damaged during the capacitor replacement. It’s tough to repair these old boards without some damage, although that’s a pretty good chunk of foil missing. If a de-soldering iron at too low of a temperature had been used – or a piece of braid – that could have happened pretty easily. All of the joints are pretty cold and looked poorly flowed, though. I re-flowed the ones that looked like it wouldn’t further damage the board with a dollop of new solder.
Underneath the board with the regulator transistors is the rectifier board and massive filter caps.
I see some leakage around the bottom. And there’s evidence of heat from below:
At this point, all the old capacitors in the power supply are candidates for replacement. It’s clear the power supply boards have suffered several failures and need a complete overhaul. There’s quite a few transistors:
More damage. Lifted traces.
The rectifier board with the large filters has quite a few large wires going to it. These are the B+, B- and ground wires for the final boards attached to the rear.
New, computer-grade filter capacitors rated a tiny bit higher than original – all while being slightly smaller.
Nichicon capacitors, some of the highest quality available, were used in this replacement.
On the left, capacitors which definitely failed – either very high ESR, out of specification, or open circuit. On the right, capacitors which were “technically ok” for now.
There’s a handful of caps on the final boards, too.
It’s time to pull the finals.
From right to left to the power resistor: signal common, signal input, b-, b+,
From left to right: TP1 bias meter point (no wire), amplifier output, ground/CT, B+, B-.
Ah yes, I seem to have found the problem:
Looks like something had a real bad time and let the magic smoke out. It’s destroyed a pair of resistors, a small-signal diode, the HW-21468 fuse resistor, a ceramic disc cap, and a driver transistor – that we know of.
Final output transistors. The amplifier board is held on by the base connections which are screw terminals through these.
The failure was so violent it scorched the board and blew one of the legs off the transistor’s case.
That’s a fair amount of dead parts. Time to hook it all back together and test some more.
Powering back up….nothing. The lights come on, voltages appeared, and nothing caught on fire – but there’s no output. Time to do some probing. Initially, I wasn’t even getting a signal out of the pre-amp stage. There are several places along the way to check for the presence of a signal on the volume gang:
After toggling several switches I did get audio to the inputs, finally. The un-failed channel was doing fine, but the other one, not so much.
The speaker protection relay is checking for proper voltages before connecting the contacts.
Something must be dragging down one of the rails. It turns out one of the sense lines was being shorted to ground; moving some wiring around corrected this problem. The relay clicked and engaged, and perfect sound started coming out – from one channel only. It was pretty clear there were some dead transistors which needed replacing also.
I replaced most of the transistors; unfortunately, the wrong part arrived and when installed caused a major short-out of several components and damaged the board with the spark. This was very unfortunate and is the first time anything of the sort has ever happened. So I tracked down a replacement final board, and refurbished that to install in its place.
This one played great as well. I tested them on my bench speakers for quite a while with the guts spread across my workbench; the bench speakers are very inefficient and this allowed the amp to get a decent work-out. Finally, it was time to get everything back together. I fixed up a bad connection to the dial lights where a resistor lead had broken. Then put it all back together.
Time to adjust the bias! Using the oscilloscope, I measured the voltage between TP0 and the speaker output terminal for a 10mV +/- 1 mV voltage difference.
Finally back in the case, and hooked up to my K-Horns for some real live testing.
The tuner section could stand to be refurbished later on to bring broadcast reception up to standard, but other than that, it sounds fantastic. Warm and rich, it consumes the FLAC audio I use for testing easily and pumps out incredibly crisp, accurate sound with a ton of power and headroom to match. It’s great to have it back in operation. I’m probably going to get myself one of these at some point, it would make a great center for my own vintage hi-fi use.
Due to the extreme amount of labor involved in a full repair on one of these receivers, Rain City Audio no longer takes the Yamaha CR series for service after several proved to be economically unfeasible. Sorry!