Student learning to troubleshoot has a couple of questions
- Thread starter WoodyJ
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Leave them alone.
Desolder the entire pin if you have to remove them. They are desoldered and pulled strait out, resist the urge twist them.
In only a few cases do you need to remove the wrapped pins. You can get to most every component by loosening the wire harness or removing a screwed structure.
Desolder the entire pin if you have to remove them. They are desoldered and pulled strait out, resist the urge twist them.
In only a few cases do you need to remove the wrapped pins. You can get to most every component by loosening the wire harness or removing a screwed structure.
When I was learning semiconductors, we did it all by hand and calulator(slide rule was just on its way out) These days ltspice is the ticket to help understand circuit theory and simulate circuit operation. go to diyaudio there is a thread devoted to ltspice.
A power amplifier is a general term just as is a "small signal amplifier". Where you draw the line is, between the two, it is rather arbitrary, I'll say >= 500m-1W into a load.
A power amplifier is a general term just as is a "small signal amplifier". Where you draw the line is, between the two, it is rather arbitrary, I'll say >= 500m-1W into a load.
I checked and rechecked all the obvious, using a CD player I tried each output, double checked speaker and tape monitor switches. I hooked up test speakers this time instead of a headphone set. The only difference was that I got a little crackle and pop when working the speaker A/B selector.
I don't know what you mean by "the rails". I've located Q29 and Q28, I know how to identify the emitters, but I don't quite understand how the test you are asking me to do is done.
Rails is slang for DC power supply voltages - sort of like the third rail of a subway line - the power line - which is supposed to be as stable and solid as a rail.
Just check that the +32v dc and -32v dc is fed to those points. Sometimes there are other parts in the power supply line that fail, like RC filters - which is a series resistor of lower value and a capacitor to ground. A power fault could burn out a resistor and leave zero volts "at the rail".. and as soon as the resistor is replaced, the UNRECOGNIZED and unrepaired fault burns the NEW one out too.
I can't be more specific, I've run out of time right now to read the whole thread to figure out what model number you are working on, and then dig it out of my Hard Drive or off of the internet.... Then start guessing where you are in the circuit.
Just check that the +32v dc and -32v dc is fed to those points. Sometimes there are other parts in the power supply line that fail, like RC filters - which is a series resistor of lower value and a capacitor to ground. A power fault could burn out a resistor and leave zero volts "at the rail".. and as soon as the resistor is replaced, the UNRECOGNIZED and unrepaired fault burns the NEW one out too.
I can't be more specific, I've run out of time right now to read the whole thread to figure out what model number you are working on, and then dig it out of my Hard Drive or off of the internet.... Then start guessing where you are in the circuit.
Ray Gianelli
Super Member
I have a Google Drive account to store all the schematics and service manuals I download. Each time I service something and find a unique trouble I document how I found it and how I fixed it, and place it in the folder for that piece of gear.
Yes, I've actually already started doing that. I'm also hooking up a web cam to record what I'm doing when I work on something, then I can go back and see how I took something apart. Right now I'm tryinig to perfect my soldering skills, I suck.
Plenty of YouTube videos on soldering. They helped me get better.
Ray Gianelli
Super Member
Before soldering, eipe the tip on a wet sponge. Then melt a dab of solder on the tip; this helps facilitate heat transfer.
A good temperature controlled iron is essential. A chisel tip is also recommended.
Like anything, the more you do it the better you'll get. When I was learning I made quite the mess of many junk electronic items, mostly TV's I found on the curb.
You'll get there.
This is what I did:
Tested voltage at the test points indicated for the idle adjustment, and they were not correct as far as cutting the blue jumpers go, so I soldered in new jumpers. Surprise! Now I had normal volume music on one channel and low barely audible volume on the other and lots of crackly noise on all the pots. I soaked the pots in Deoxit and left it alone for two days. Crackly noises went away but no change on the weak channel. I decided to pull the volume pot so I could test out of circuit. Surprise again! Text book cold solder joint on one of the posts on the pot, perfect separation circle, dull solder, a picture right out of my text book. Pot tested fine, resoldered it AND I FIXED THE *****ING THING! Sounds surprisingly good, too. The volume pot is mounted on a seperate circuit board you can barely see the reverse side of, I didn't find it until pulled the pot with the board out and flipped it over. But I did one other thing, while the Deoxit was doing its work, I desoldered the power transistors and control section transistors so I could practice de and re soldering along with checking transistors with my DMM and my new nifty $25 transistor tester from the hilariously named Banggood Co, so who knows maybe I accidentally fixed something doing that. I think someone tried to fix the weak channel by cutting the jumpers, made it worse and gave up. Anyway, my Dad is listening to John Prine on it right now, he thinks I'm a genius.
Tested voltage at the test points indicated for the idle adjustment, and they were not correct as far as cutting the blue jumpers go, so I soldered in new jumpers. Surprise! Now I had normal volume music on one channel and low barely audible volume on the other and lots of crackly noise on all the pots. I soaked the pots in Deoxit and left it alone for two days. Crackly noises went away but no change on the weak channel. I decided to pull the volume pot so I could test out of circuit. Surprise again! Text book cold solder joint on one of the posts on the pot, perfect separation circle, dull solder, a picture right out of my text book. Pot tested fine, resoldered it AND I FIXED THE *****ING THING! Sounds surprisingly good, too. The volume pot is mounted on a seperate circuit board you can barely see the reverse side of, I didn't find it until pulled the pot with the board out and flipped it over. But I did one other thing, while the Deoxit was doing its work, I desoldered the power transistors and control section transistors so I could practice de and re soldering along with checking transistors with my DMM and my new nifty $25 transistor tester from the hilariously named Banggood Co, so who knows maybe I accidentally fixed something doing that. I think someone tried to fix the weak channel by cutting the jumpers, made it worse and gave up. Anyway, my Dad is listening to John Prine on it right now, he thinks I'm a genius.
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Congratulations! Feels great, right?
Welcome to the club! On to your next restoration! What do you think you want to work on next?
Feels great ! Damn straight! So what's my $25 garage sale amp worth now? Am I going to be rich ?
Many vintage receivers and amps will bring $300 to $600 if you make them look good and recap and repair all that they need. It's not really profitable if you actually pay yourself for your time, but I find it FUN and I learn something every few minutes. Totally worth it for me.
One thing to watch out for are any gear with "unobtainium" parts. Gear earlier than 1972 or so will likely have Germanium transistors which are really tough to find and expensive, so you have to learn which brands and which models have those. Similarly, many 1979 or later models have custom or short-lived amp modules that aren't made any more and hard to find and expensive to buy. Not impossible, just difficult. Avoid those, too.
Most everything in between uses discrete silicon transistors and diodes that are easy to find suitable (and often better) modern equivalents for.
Then you can get and restore a few cap-coupled receivers and compare them to direct-coupled ones (that you find and repair) and then you'll have the "circuit design makes a difference!" bug and by then you're hooked.
Once you have a degree and a few years getting a bigger and bigger paycheck you can start repairing (or building from scratch) tube-based gear to round out your audio range experience and by then your hopeless. Don't follow this path if you plan to get married, have kids, or anything else that competes for hard-earned dollars and square footage and shelf space in your home.
Have a blast! Tell us what you're working on and give us more opportunities to give you a few second opinions.
Cheers!
Most everything in between uses discrete silicon transistors and diodes that are easy to find suitable (and often better) modern equivalents for.
Then you can get and restore a few cap-coupled receivers and compare them to direct-coupled ones (that you find and repair) and then you'll have the "circuit design makes a difference!" bug and by then you're hooked.
Once you have a degree and a few years getting a bigger and bigger paycheck you can start repairing (or building from scratch) tube-based gear to round out your audio range experience and by then your hopeless. Don't follow this path if you plan to get married, have kids, or anything else that competes for hard-earned dollars and square footage and shelf space in your home.
Have a blast! Tell us what you're working on and give us more opportunities to give you a few second opinions.
Cheers!
I appreciate everyone's help with this. If I could ask another "dumb kid" question, I'm sure Ohm's Law plays a big part in your work to diagnose a problem in circuits and I know it is absolutely essential to understand it. What about Kirchoff's Laws 1&2 ? Essential or not? I'm still having a tough time wrapping my head around them. When and if it is essential, do you do the calculations manually or do you use a software utility? Or is it something that only circuit designers would use? Can it be used to find a defective part?
They are part and parcel of our intuitive understanding, yet only very rarely do we employ then numerically.
Have you looked at the Wikipedia link :?
Divider Circuits and Kirchhoff's Laws chapter from Lessons In Electric Circuits Vol 1 DC free ebook and Lessons In Electric Circuits series.
Have you looked at the Wikipedia link :?
Divider Circuits and Kirchhoff's Laws chapter from Lessons In Electric Circuits Vol 1 DC free ebook and Lessons In Electric Circuits series.
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