My next patient on the table is a Fisher SR-2010 receiver with no output.
Basic examination revealed a burned 100 Ohm, 1/4 Watt resistor, labeled as "R60", caused by a shorted transistor. The bad transistor is the slightly-out-of-focus grey device with the tab at the top.
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Since the transistors originally used are obsolete, I have to locate substitutes. I have the data sheet for the OEM transistors, so I know the parameters. Several members over at the AudioKarma forum have gone through the process of selecting replacements with modern parts, so that's how I'll go after I read a hundred posts or so....Since the substitute will have somewhat different characteristics, and it's in a "balanced" configuration, I'll replace both of them. And I'll do the same for the other channels. I also noticed half-a-dozen electrolytic capacitors that should be changed. Their maximum working voltage is 63 Volts, and they're on a 60 Volt supply. They're loud, messy accidents just waiting to happen.
Before I started on this, I checked all the controls for smooth operation. All of the switches need cleaning, their mounting hardware was loose, and several of the push buttons are sticky. Simple job cleaning them, but it takes time.
One thing that really bugged me was that the tuning knob had a scratchy, notchy feel to it. It also made a "tic tic tic" noise as you rotated the knob. Further investigation revealed the operating shaft for the tuning capacitor was a tad loose....
So since the dial calibration is now completely borked, and I have to disassemble the capacitor to find out what happened, it looks like I'll be restringing the dial cord with a new one. Which means off with the front panel.
Which revealed a cracked light diffuser under the panel.
A drop of thin acrylic cement, acetone, or toluene will hold it together once I get it realigned.
I'll do my usual "Clean-and-Shine" and replace all the dial lamps, which are quite darkened with age. Should be quite pretty when she's finished.
Annnnnd out in the garage, work proceeds on the Supra. I needed to know the current draw of my new fans so I can size the new wiring and fusing, so I made a little lash-up to power the fans while I measured the current.
I used some 10 gauge red/black cable, and a fully charged Optima Yellow Top battery. The clamp-on ammeter is one that also reads DC Amperage, and it showed a running current draw of about 5 Amps, with a brief surge to 20 Amps when the fan is powered on.
Total Rain for April.....
Have a good, safe week, and don't forget to check your six.
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I'm not too familiar with Fisher gear. It looks like it is a nice piece of equipment and should clean up nice given your meticulous skill set.
ReplyDeleteI'm not either! It's straight forward audio/RF stuff. It's nicely made, very good soldering, but I was surprised to see them running caps that close to their max WVDC.
DeleteGood gravy, I remember when my oldest brother bought that receiver! I used to stare at the thing like it was a console at Mission Control at NASA. I wasn't allowed to open the glass cabinet case it was in. Cosmetically that unit is gorgeous. She's going to be mighty fine if you can get it running. What will you do with it?
ReplyDeleteI'm repairing it for a local guy. His wife turned it on, the smoke came out of the resistor, and no music! It's in excellent physical condition except for a bit of wear-and-tear. Not sure exactly when it was made, but it's in the 1979 Fisher catalog.
DeleteLooks like you'll be 'busy' with that one! And we've had 8 inches of rain in the last WEEK!!!
ReplyDeleteIt's not too bad. The electronics and cleaning is pretty straight forward. The tuning mechanism is going to be a bit fiddly, but I'll get it.
DeleteEIGHT INCHES in one week!?! YOWZIR!