Sanyo M-X720
The MX720 (also known as the MR-X5 in Japan) was introduced in 1981. It was one of Sanyo's largest boomboxes, measuring 604mm (23.8") wide and 307mm (12.1") tall, not including the handle. It weighs 17.5 lbs empty without batteries. Available models included the MX720, MX720K (which had shortwave), and the MX720LU which was apparently sold in Europe.
It's one of the rarest Sanyos. Perhaps it did not sell very well? We can't imagine why it wouldn't. It's a very good-looking model, with shiny metal trim, big VU meters, and nice blue trim rings around the woofers. It also sounds fantastic. Very clear and accurate. Its tape deck frequency response is allegedly 30 to 17,000 Hz when using Metal tape. That is very good for a boombox.
Inside, it is very well-built, with a removable inner chassis supporting all the electronics, a flywheel tuner weight, and grid-shaped anti-vibration molding on the inner surface of both the front and rear cases. The speakers include 6-inch, 2.5 ohm woofers (part number 4-151T-37200A) and 1.5" tweeters. The service manual says that power output is 2x11 watts maximum "music power", but "music power" is not an accurate measurement. Let's look at the amplifier chip and Google its specs. It is a Sanyo LA4440, which is rated for 2x6W @ 13.2V into 4 ohm and 10% THD. But the M-X720 is a 15V boombox with 2.5 ohm speakers, so the output will be higher than that.
A copy of the service manual can be purchased HERE
). There are some common issues with this model. First, the antenna mounts inside the case might crack. If this happens, the antenna posts will seem loose. You can go inside and repair the mounts with plastic cement. Secondly, the rotary tuner band switch might become loose. You will need to go inside and tighten the nut that braces it against the internal chassis. Additionally, if the tape deck is jammed with the heads up and the lights always on, it's because the belts slipped. You will need to either replace the belt(s), or for a temporary fix you can go inside and put your fingers on the metal flywheel behind the deck, and rotate it clockwise until you hear the heads click back down. Finally, I have seen several examples of this boombox with shattered or fractured Power Supply boards. This condition can exist even when there is no outward signs of physical damage to the case. The reason has to do with the fact that the power transformer used on this model is fairly heavy and is soldered directly to the PCB. The manner in which the transformer and the circuit board itself is then mounted onto the case creates a condition where a heavy shock (from a drop, or due to heavy handling during shipping) can cause the transformer to rotate due to inertial forces and twist the circuit board (which itselt is anchored and unable to rotate with the transfomer) causing it to fracture. The folks at AnalogAlley.com are currently working on a replacement solution for examples with this problem. Contact them there if you are in need of help.