Radio repair advice, please

You might look on ebay for some of the old signal generators. There are also some signal generators and some are in kit form from China called DDS.

The simpliest way I know of is something I used a long time ago. It was something I built out of parts I had from a magazine. It was just a multivibrator operating at some audio frequency ,but it had harmonics way up into the RF range. There was also some comercial versions of it. I think it only used 2 transistors a few resistors and capacitors. Like this ebay number. You start at the audio stage and work to the rf area. I usually put it on the volume control pot first. That seperated most of the audio stages from the RF section. One of the beter ways to trouble shoot equipment is to do the half way method. Start about half way through the circuit and when you loose or gain the signal, go half way to the last or next section.

251121615025

You'd have to be nuts to buy an ESR meter just for one radio. Save the money and just replace all the electrolytics. For a signal to inject a single stage oscillator for the required frequency would be the cheapest solution; loads of schematics on the web and it doesn't need to be a crystal controlled job.

ESR meters are cheap and reliable. Back when I bought my first one in 1985, they were $1200. I still have it.

For what they cost these days, there's no reason a hobbyist shouldn't own one.

Plus, for ones like the Bob Parker design, you get some soldering practice as well!

John :-#)#

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They're not *that* cheap (I bought one a few weeks ago and it cost me 90 quid ($135) and if the OP is only going to be doing the one radio, which he got for free, he'd have to be nuts buy a meter!

If you have to pay around $ 100 that is too much for just a couple of repairs. For less than $ 20 including shipping, anyone that wants something inexpensive to check components should check this or one like it out on ebay. Peak makes about the same thing in a case for around $ 100 but they make one for transistors and another for the capacitors and resistors. They charge you twice for the same thing.

The one I bought is a Peak. Good quality item, but all it measures is ESR.

Except, these electrolytics are just handling AC line or audio frequencies. They may have expired, but not from strain of 100KHz or whatever.

Also, they aren't used in some highly-feedbacked circuit, as is the case with switching supplies. Transistor radios use more electrolytics than tube radios (which could be often diagnosed by listening to the radio, hum meant a new filter capacitor, low audio gain meant a new cathode bypass capacitor in the audio stages), but they are straightforward. They are either bypassing the emitter resistor in the audio stages, coupling audio between stages, or to provide a low impedance on the "B+" line. It's daunting to look at, all those electrolytics in a transistor radio, but you don't need anything fancy to replace them with, and if you aren't going to troubleshoot (low audio, bad bypass or electrolytic coupling capacitor, motorboating, bad electrolytic on the "B+" line), then just replacing them all is relatively cheap (compared to buying an ESR meter) and fairly fast.

Michael

I'll see how my $15 component tester works when I get it.

Greg

Thanks everyone for your thoughtful answers. Reason for ESR meter is I do have 2 additional radios (not a priority) and 3 old guitar amps that I might get to in my old age.

A previous poster (above) referred to an inexpensive ESR (possibly a kit) but did not leave a link. Any suggestions?

Ivan Vegvary

First of all, there are really only a handful of electrolytics in the

2000, many of the caps are ceramic (you don't need an ESR meter). The most likely problem you will run into is intermittents in transistor sockets, switches, etc. - easily fixed with re-seating &/or some contact cleaner. The dial strings on these also have a habit of slipping/breaking and are kind of tricky to get to.

I think you are putting the cart before the horse, here. Unless you have some heavy corrosion or other damage, you have a good chance of coaxing some audio from the set. If you have a scope, you can generally use an over-the-air signal to check out the rest of it. Unless the front end is totally dead (unlikely scenario), I wouldn't worry about getting a generator right away.

The "Blue" ESR meter is regarded as one of the best. You can get the kit directly from here:

It would be interisting to compair that with one of the $ 20 component testers from China.

One thing that I think might be wrong with the testers is they use almost no voltage (less than 1/4 of a volt). I just wonder if the usually higher voltages the cpacitors operate under would make any differance, especially the power supplies that have over 100 volts on them.

The lower the better when it comes to voltage.

I don't use an ESR meter anymore, I use a 1 kHz 400 mV square wave with a s ource impedance of about 360 ohms. I apply it to the scope probe and the DU T and observe the rising and falling sides of the resultant waveform.

The Creative Electronics Wonderbox used less. One elcheapo meter I ran acro ss used less.

Less than a half volt is good because then semiconductor junctions do not i nterfere with the readings.

I am not that crazy fond of digital meters when it comes to this. The Dick Smith is good and everything and there was another one I used for a while. The one I used went through a rigamaroll every time you put the probes on " discharging". Fuck discharging, you have a coupling cap internal - use it a nd measure the ESR NOW. I have 50 to test in this unit and I got about 10 m inutes to do it.

I just want the needle to move or a bar graph of LEDs to light up or someth ing. I do not need to know the ESR to the fifth decimal place. Nor do I nee d it to beep. Actually if someone came up witt an audio indication of a use ful type I would be interested.

Now the problem with that is if it say, emits a sound when the cap is good, fine. But it is hard to hear different levels of sound. More accurate woul d be if the DUT shorted out the audio, but that would mean the audio going on all the time until a good capacitor is connected to the test leads. When completely silent the cap is good, but htis method would be quite annoying .

I do not need a digital readout. The Dick Smith is a fine and accurate inst rument, but when my boots are on the ground I just need something quick. Th is is not formulating some delicacy with saffron and truffles, this is maki ng chili. Is it an ohm or less or not ? And then in some instances, how muc h less ? If the leads are farther apart in solid state equipment you usuall y want it under an ohm. The smaller ones are not as critical, that's why th ey used smaller ones.

Another fairly common problem is one or more of the germanium transistors becoming leaky.

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