JohnW Posted February 10, 2022 Share Posted February 10, 2022 So I bought this receiver for $200, and it was DOA. Seller assured me it worked when he sent it and I believed him. So I removed the top and bottom covers and found all the fuses. One of them, FU1 (from the wiring diagram) a .5A fuse, was nonconductive. Aha! I didn't have a .5A fuse, but I did have a 1A fuse. Popped it in, and it worked! And then the resistor (R9) connected to the fuse started smoking. And then the the sound cut out again. Yes, I feel like a bit of a dumbass. .5A fuses have been ordered. And I'd love to buy a replacement resistor, but I cannot, for the life of me, identify what it is. I found it on the wiring diagram in the 430 service manual, but it's pretty much unreadable (see attached screen cap). I can't locate the resistor in the parts list nor in the schematics. But I am not terribly experienced readin schematics. Could someone please identify the resistor so I can get one, install it, and pick up where I left off? Thanks in advance. Quote Link to comment Share on other sites More sharing options...
Davecv41 Posted February 10, 2022 Share Posted February 10, 2022 The fuse was blown, it got replaced with a larger current fuse, then the over current turned R9 into the weakest link in the circuit. It sounds like you have a short circuit, and you need to find it, otherwise you can keep replacing the fuse and the resistor until the cows come home, and still have no music. 1 Quote Link to comment Share on other sites More sharing options...
JohnW Posted February 10, 2022 Author Share Posted February 10, 2022 11 hours ago, Davecv41 said: The fuse was blown, it got replaced with a larger current fuse, then the over current turned R9 into the weakest link in the circuit. It sounds like you have a short circuit, and you need to find it, otherwise you can keep replacing the fuse and the resistor until the cows come home, and still have no music. Yes Dave, I know that. Can anyone identify the resistor? Is that 8.5 watts? Quote Link to comment Share on other sites More sharing options...
captainbeefheart Posted February 10, 2022 Share Posted February 10, 2022 5 hours ago, JohnW said: Can anyone identify the resistor? Is that 8.5 watts? EDIT: I found where it is and what it does. It's 8.2 ohms 1/2 watt It is in series after the fuse from the transformer to the bridge rectifier D6 on "rectifier board A". Check the bridge rectifier D6 and also check the regulator transistor Q1 for shorts. Also check D7 the reference zener diode and all the capacitors around Q1. 2 Quote Link to comment Share on other sites More sharing options...
JohnW Posted February 10, 2022 Author Share Posted February 10, 2022 34 minutes ago, captainbeefheart said: EDIT: I found where it is and what it does. It's 8.2 ohms 1/2 watt It is in series after the fuse from the transformer to the bridge rectifier D6 on "rectifier board A". Check the bridge rectifier D6 and also check the regulator transistor Q1 for shorts. Also check D7 the reference zener diode and all the capacitors around Q1. Thank you, will do. I checked everything on Rectifier Board A last night for shorts, and they were all good. But obviously they weren't shorted, because current is obviously passing through them. I'm a novice at this sort of thing. Appreciate the help. 1 Quote Link to comment Share on other sites More sharing options...
captainbeefheart Posted February 10, 2022 Share Posted February 10, 2022 1 minute ago, JohnW said: Thank you, will do. No problem good luck Quote Link to comment Share on other sites More sharing options...
JohnW Posted February 10, 2022 Author Share Posted February 10, 2022 Here’s the front side of Rectifier A board. Those solder points look a bit crispy. Pic 2 is the other side. I’ve no idea what I’m looking at, but a used Rectifier A board is $29.99 on EBay. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 10, 2022 Share Posted February 10, 2022 Pretty standard looking rosin core uncleaned up solder joints. 1 Quote Link to comment Share on other sites More sharing options...
JohnW Posted February 11, 2022 Author Share Posted February 11, 2022 That Sirba diode has four leads. Not sure how to test it. Quote Link to comment Share on other sites More sharing options...
Marvel Posted February 11, 2022 Share Posted February 11, 2022 It's the bridge rectifier. You can reference them online. The two middle pins connect to the a/c and the ends are marked for the positve and negative. 2 Quote Link to comment Share on other sites More sharing options...
JohnW Posted February 11, 2022 Author Share Posted February 11, 2022 17 hours ago, Marvel said: It's the bridge rectifier. You can reference them online. The two middle pins connect to the a/c and the ends are marked for the positve and negative. Sirba tests good. Quote Link to comment Share on other sites More sharing options...
JohnW Posted February 11, 2022 Author Share Posted February 11, 2022 17 hours ago, Marvel said: It's the bridge rectifier. You can reference them online. The two middle pins connect to the a/c and the ends are marked for the positve and negative. Sirba tests good. Will know more when the proper fuse and resistor arrive tomorrow. 2 Quote Link to comment Share on other sites More sharing options...
captainbeefheart Posted February 11, 2022 Share Posted February 11, 2022 2 hours ago, JohnW said: Sirba tests good. Will know more when the proper fuse and resistor arrive tomorrow. Move on to that transistor bolted to the heatsink right next to the bridge rectifier. Use a diode tester and check the transistor base-emitter and collector-base. Check it for shorts also. Quote Link to comment Share on other sites More sharing options...
JohnW Posted February 11, 2022 Author Share Posted February 11, 2022 10 minutes ago, captainbeefheart said: Move on to that transistor bolted to the heatsink right next to the bridge rectifier. Use a diode tester and check the transistor base-emitter and collector-base. Check it for shorts also. Any tips on how to "check the transistor base-emitter and collector-base?" I have no idea what that means. Quote Link to comment Share on other sites More sharing options...
captainbeefheart Posted February 11, 2022 Share Posted February 11, 2022 5 minutes ago, JohnW said: Any tips on how to "check the transistor base-emitter and collector-base?" I have no idea what that means. I guess first just check for shorts, if your resistance meter beeps continuity between any pins it's junk. Transistors are current controlled devices. An NPN will have normal .6v diode drop between base and emitter. This small amount of current allows a much larger amount of current to flow between collector and emitter. The collector will also have a normal .6v diode drop between base and collector. Most multimeters have a diode test setting. Place red probe on the base pin and touch each emitter and collector pins with the black probe, you should see the normal .6v drop for both base to emitter, and base to collector. Think of a PNP transistor as the diodes reversed. The 2SC1212 is an NPN so don't worry about testing a PNP type. Quote Link to comment Share on other sites More sharing options...
JohnW Posted February 12, 2022 Author Share Posted February 12, 2022 Thanks, and how do I determine which pin is the "base pin?" Quote Link to comment Share on other sites More sharing options...
babadono Posted February 12, 2022 Share Posted February 12, 2022 Service manual no help? Can you read the device # on it? Google is your friend for finding device data. The collector is the electrode that is the tab that is bolted to the heatsink. This will also be 1 of the 3 leads. It maybe insulated electrically form the heatsink. Once you determine which lead is the collector the base will read a diode drop away as the Captain explained. Quote Link to comment Share on other sites More sharing options...
BadChile Posted February 12, 2022 Share Posted February 12, 2022 Going from memory here so use Google to check me and listen to others, but if your multimeter has a diode function, test between any two legs, and then swapping leads. Do all six possible combinations using all three pins, of which two and only two will measure a 0.6V drop. I had my 430 open today as I was swapping out the input/output jacks and completely forgot about this post. Will likely have it open again in 10 days or so for another mod and if you're still having problems I'll poke around and see what I see. But others on this thread are smarter than me so I suspect you'll be sorted well before then. Quote Link to comment Share on other sites More sharing options...
captainbeefheart Posted February 12, 2022 Share Posted February 12, 2022 4 hours ago, JohnW said: Thanks, and how do I determine which pin is the "base pin?" Most transistors come in standard packages like TO-220 or TO-3 etc...... which have a standardized pinout. If you are ever in question look up the datasheet, if you are designing a circuit you should be looking at the datasheet anyway. I don't expect everyone to know this stuff but for future reference. For the 2SC1212 the pins are ECB from left to right (123). Put the red test lead from your diode tester to the right most leg which is the base (pin#3) and touch the other two pins (emitter and collector) with the black test lead to see if each has a .6v diode drop. Flip the leads around and put the black lead on the same base pin, furthest to the right (pin#3) and you should have zero continuity with the same test, infinite resistance, open line (OL). It's the same way you would test a diode, in one direction with the meter you will have a .6v diode drop, flip the leads around and you shouldn't have any continuity. Good luck 2 Quote Link to comment Share on other sites More sharing options...
JohnW Posted February 12, 2022 Author Share Posted February 12, 2022 Yes, but it was only a .3v diode drop on both pins—reading went from 1.0 to .692 Quote Link to comment Share on other sites More sharing options...
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