Friday, 20 January 2012

In the span of just a few weeks I have come across 3 vintage Sony receivers of the same series and approximate age. I bought one, the STR-7025 for $35, and was given an STR-7035 for free (though I did give the guy a Pioneer SX-535 that cost me $10), and just the other day I saw but did not buy an STR-7065 at the local Salvation Army store.

Just a bit odd to see so many in a short span, as I really never noticed this series before. The 2 I do have are going to turn into one project.

For one, the 7025 has a problem with the FM tuner but it works fine in everything but FM. The wooden case is in quite good shape and the front panel is practically mint. The 7035 has a better looking case (though has a drivers license number scratched into the side...I hate that!) and I swapped one knob from it to the 7025 but it has an even bigger issue than the 7025 so it becomes the donor to keep the other alive.

The fellow I got it from had plans to re-cap it, as in replace the capacitors on the circuit boards. The theory goes that the capacitors dry out over many years and their characteristics change which alters the sound quality of old audio gear. In a worse case scenario it will cause the entire device to fail. It's actually not a theory; it does happen. Sometimes the differences in sound though are probably overstated but they can be heard if you have the right ear and the right gear.

Anyway, the guy got to the point of removing all the capacitors from the power supply board and the amplifier board, but did not solder in new ones. I think he got bored with the process or burned himself with his soldering iron and gave up. So I got a receiver with a baggy full of caps inside it.

I knew it wasn't working when I got it from him, and he did say more or less what he did but I was still a bit surprised when I opened it up. That's ok, as it was free after all. I could sell the knobs alone or maybe get a few bucks locally or just give it away again. However I have other plans...

The tuner board seems to be intact. It also appears to be identical to that of the STR-7025 with the non functional FM section. So my plan is to swap it over. I think.

I could also replace the caps in the 7035, but that is not as easy. When I realized the extent of the situation in that unit I went looking for the Service Manual and I did find it on ebay. Having that with the schematics and parts list will help a lot as I don't know what value capacitor goes where without it. If I were replacing caps from scratch I would do one or two at a time, not "remove all, replace all" as it would get confusing fast.

One concern I have is that I don't have any way of knowing if the tuner board on the 7035 works any better (or at all) than the 7025. I also can't easily test that before making the swap. There are at least a dozen wires connected to the board, plus the tuning capacitor and display string pulley, and the AM antenna coil.

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