Schematics

Thread Starter

Six_Shooter

Joined Nov 10, 2012
34
(Sorry trying to keep title short, after reading about some issues of titles 20 characters or more long.)

I sometimes come to times where I (need) could REALLY use a schematic for something I'm working on, where do you guys find schematics for electronics, that you would be repairing?

Currently I'm trying to repair an old radio, and while it's fairly simple, there's a lot of through hole devices on a very cluttered (one sided) circuit board. I have two of these radios, one works, and the other just makes some buzzing noises through one of the transformers, only when the volume is turned near and at maximum, but nothing comes out of the speaker. I haven't found any obvious failures yet, but a schematic would help me trace through the circuits much more easily and zero in on most likely areas of issue.

Thanks
:)
 

Thread Starter

Six_Shooter

Joined Nov 10, 2012
34
Oh, because it's not just old radios that I'm interested in getting schematics for, but that's just what I currently happen to be working on.

Besides, "Schematics for old radios" is 25 characters, which is over the magic number, as it would seem, of 20 characters. ;)
 

takao21203

Joined Apr 28, 2012
3,695
Imagine if everyone writes:

Polarity
Overheating
Factor
Voltages

OP should check museum websites for radios or portals that sell such radios.

I saw an old VFD clock on a museum site, and wrote an email asking where I may get one of these. The admin sent me an eBay link.

If you don't know these kind of circuits already, then almost forget about it, unless you have plenty of time to learn about these circuits.

I also have an old tube circuits manual somewhere (as PDF).
 

Thread Starter

Six_Shooter

Joined Nov 10, 2012
34
To be specific, the radio I am currently working on, does not use tubes. It is an Hitachi radio from a 1971 Datsun 240Z, I'm not modifying it, I am repairing it, or at least attempting to. I have a second identical unit from a 1972, but would rather keep that one in my possession, the one I am repairing is for a friend.

Thanks for assuming I know nothing about electronics. :rolleyes: I'm simply looking for sources of schematics, because I've had mixed success in the past when searching for them.

Don't you find it easier to repair something when you have a schematic?
 

takao21203

Joined Apr 28, 2012
3,695
The circuit board may have reached end of life, especially if it is containing electrolytic capacitors.

I mean you maybe repair it, and a year later something else will fail.

I had one computer board here from the mid 1980s. It powered up, booted from the floppy, but then became erratic. After a few hours, it stopped working altogether. Almost certainly due to electrolytics end of life.
 

Thread Starter

Six_Shooter

Joined Nov 10, 2012
34
If I have to replace all of the components, so be it, that's not the point of the original discussion though, which is where do people find schematics for the electronics they are repairing (or possibly modifying)?

I'd rather not take the time to draw out the circuits by hand, I really don't have the time to do that currently.

I guess I'll replace the most likely culprits and go from there. The biggest issue with this particular radio is that the circuit board is not easily removable, there are some solid jumpers that connect between the circuit board and other components, not like modern radios that have plugs. ;)
 

Thread Starter

Six_Shooter

Joined Nov 10, 2012
34
I have that radio owners manual (though an original copy). :)

No, the schematics are not in it. :)

I also have the factory service manual, which does not include the internal schematics of the radio.

The You Tube link is not work, but yes, the tuner section is quite interesting, to say the least. After observing it's function, I think I could swap one of the AM presets for an FM preset, but I'm not too worried about something like that at the moment. I have an aftermarket radio in my 240, and plan to keep it that way, though I do prefer the look of the original.
 

takao21203

Joined Apr 28, 2012
3,695
Chances are such schematics were never released to the public, because repair seems to be too difficult, and it is a consumer grade product.

Not many repair shops remained intact business over 4 decades. And nowadays, it is not a big business anyway. I don't think car radio circuit boards are repaired very often nowadays. At best, they plug in a new PCB, a new decal, but only for expensive radios.
 

Audioguru

Joined Dec 20, 2007
11,249
My first job was repairing Chrysler car radios on the Philips production line then i was quickly promoted to engineering them.
Philips invented the compact cassette tape deck which was installed to replace the old 8-track tape player. The amplifier in the radios used germanium output transistors driving a small stepup the voltage transformer.

I bought a Blaupunkt German car radio for my 1975 German Volkswagen then ordered the service manual. The Chinese! manufacturer's name was blacked out with a felt tip pen. All the parts were Chinese.
The car radio recorded stereo from the radio on compact cassette tapes and I souped it up to be hifi.
 
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