Hi guys. I just inherited my father's old Realistic STA-64 receiver, and it's been working without a hitch, except for one problem: every once and a while (and this is very rare) the speakers will suddenly make a louder BRRRRP sound and the sound will stop coming out, even if I power down the receiver totally and turn it back on. In fact, the only thing that will "reset" the speaker to playing normally is popping out the receiver's fuse and popping it back in again. What's especially weird is it always will happen during the same "sounds" (i.e. exact same moments during films) making me think it's tripped by certain frequencies. However, whatever the sound is that's triggering this behavior, it's not actually something obvious to the human ear. Anyone got any ideas on how I could fix this?
Fix it? as in you diagnosing the defective components without a schematic and actually performing the repair work yourself? Nope, not a clue.
Components wear out and they die. This is especially true of older components with older parts which have been in storage for years. Once a component has been in storage it should never be plugged directly into a 120VAC outlet the first time it is powered back up. It should be placed on a scope and a signal generator and fed a slowly increasing amount of voltage while its current draw is monitored. Plugging it directly into a 120VAC outlet only hastens the effects of aging on the internal components.
The Radio Shack receivers were never manufactured by Radio Shack but were always built for RS by another company. That meant the RS products could only be repaired by RS techs. My recollection, through all the numbers RS produced, would be your receiver was a product of the late 1970's? You can call RS and ask if they will provide an estimate of repair costs - if repairs are possible. Often components older than a few years cannot be repaired since direct replacement parts for older gear such as your reciever simply will not exist. An estimate should run less than $100. If you can and if you decide to go further into a repair, that money will be put towards the total repair bill.
That will fix the immediate problem but cannot address any future problems likely to occur in an older amplifier. Unless you had the unit completely rebuilt from stem to stern other things are very likely going to go wrong with this receiver.
Consider the value of having put, maybe, $150 into this receiver only to have more problems in a month. No one can truly predict what might happen and no tech can repair what is not broken so the receiver must break again before the tech can replace a defective part. What else could you buy with the money you will be putting into this old receiver?
As I said, most RS products are not going to be serviced by non-RS techs. They won't have product information or access to any out of the ordimary parts used in the component. If you would like to have further information on how to proceed, I would contact http://www.atlasaudiorepair.com/. They specialize in repair of vintage gear.