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 Post subject: EICO 320 Signal Generator Need Help
PostPosted: Jan Fri 26, 2018 2:10 am 
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I picked up an EICO 320 Signal Generator at an antique shop for what seems like an amazing $8. I am 19 and have no electrical experience. I am not even quite sure what it's purpose is, but I like it a lot, and want to fix it up rather than sell it if I can find a use for it.

When I plugged it in, it blew the circuit breaker. (I didn't use an isolated outlet.) The unit itself is in fairly good shape. The capacitors look like old ruptured batteries but again, I have no experience with these things. I will attach images, I think the main dial for the signal frequency is out of alignment, and after turning a bit a part has come off. It doesn't turn easily and the knob won't turn it at all, you have to push on the plastic arrow.

If anyone can help out in any way, perhaps even with a link to the manual, it would be greatly appreciated. And I am a new user, so if this is in the wrong forum please move it, apologies.

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Also of note, at the same store I saw two tube testers. They looked in rough shape, the only part left was the front plate with all the switches and wires. One was $7 and one was $10. Are they worth picking up, possibly to resell?


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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jan Fri 26, 2018 1:27 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 1684
Location: Sunbury, Ohio 43074
Hello Erik and welcome to the forum. You have picked a difficult "first project" ... since to see if it is working, assuming you were able to fix it, you need other test equipment. It's purpose is to generate RF (radio frequency) signals to test radios, some parts of TV's, and the like. As to whether or not it is worth fixing, fully restored ones sell for about $50-75 so you decide. It appears that, sitting on the table there next to the knob, is part of the tuning variable capacitor. If that is the case, you will not be able to repair (will need a replacement tuning capacitor) it and the instrument is probably not worth the effort.

You are fortunate that all that blew was your circuit breaker when you plugged it in. The instrument could have gone up in smoke. Or sent you flying across the room. You have to start with the basics here .. is the Power Cord itself OK ? After that would be resistance measurements of the power transformer to see if it is perhaps shorted to ground, which would also blow your breaker. My guess is that the electrolytic capacitors might be the cause of this, unless of course it turns out to be the power cord itself.

To safely work on this instrument, you need an isolation transformer, and a variac to slowly power it up. And a lot more knowledge of electronics. I'd start by reading everything you can possibly find, starting with links on this very forum on repairing THIS instrument, and then search for capacitors, other topics.... Electronics is a fascinating hobby, and even a good vocation, but as with anything else you need to learn the basics before jumping into the pool. Working on this instrument is rather more like "the pool" than the basics.

To begin in this endeavor, you will need at minimum a working multimeter such as one you can even find at Home Depot, that measures AC and DC volts, ohms, and amps. And a soldering station, knowing how to solder, and the above mentioned isolation transformer for safety, and a variac so old equipment does not go up in smoke the first time you power it up. AND of course, knowledge on how to use all of that.

As for the tube testers you mentioned, I'd pass on those unless you can supply us a make and model number. My guess is that they are worthless, but if one of the more popular ones might be worth picking up for later. You need to learn a lot more before you tackle one of those critters.

my 2c

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Last edited by Barry H Bennett on Jan Fri 26, 2018 1:46 pm, edited 1 time in total.

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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jan Fri 26, 2018 1:33 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17589
Location: Albuquerque, NM 87123
It appears that your variable capacitor is damaged beyond repair; you will need to get a replacement at the very least. Next you will need to replace most of the capacitors to make it reliable. Tripping the circuit breaker is not a good sign; perhaps it's just a shorted line cord.


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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jan Fri 26, 2018 2:47 pm 
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Here's a link to the instruction manual:
http://bama.edebris.com/manuals/eico/320/


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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jan Fri 26, 2018 4:50 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3060
Location: Seattle WA US
Erik-
Welcome to the forums. For a start, there is a concentrated amount of good advice in the book, Fundamentals of Radio Servicing. This book is available free, for you to download, in the Archives area of this website. Your signal generator is very much like a radio in terms of how to service it, and what tools you will need. With this book and the Eico manual you will be on your way to understanding and fixing the signal generator. Come back to the forum when you have questions.

Concerning the tube testers, I would advise avoiding equipment that is not reasonably clean and apparently complete, no matter how cheap it is.

-Chuck K7MCG


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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jan Fri 26, 2018 5:23 pm 
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The variable capacitor may be repairable. The shaft appears to be misaligned and displaced from the rear bearing. That would explain the difficulty turning the tuning shaft. Once you fix that misalignment, you may be able to re-attach the rotor plates to the shaft. You'll need to ensure that they are centered between the fixed stator plates. The rotor plates should engage with the slots on the tuning shaft. A drop of superglue may be needed to hold them in place. Clean everything with lacquer thinner and a brass-bristle brush first before trying to glue it.

If you can't repair it, the tuning capacitor is just a single-gang 360 pF variable capacitor, although it perhaps has a 3:1 reduction drive built in to it. You could find a substitute, for example:
https://www.mikeselectronicparts.com/pr ... tor-384pf/

The 320 has a power transformer, so you don't absolutely require an isolation transformer. You should first disconnect the old line cord and then check that the primary of the 320's power transformer doesn't have any leakage to the chassis by using a multimeter to measure the resistance between each of the terminals of the primary and the chassis. It should be essentially infinite resistance. If not, then you will need to replace the power transformer before continuing.

You don't need a variac either. You should build a dim-bulb tester instead:
https://www.antiqueradio.org/dimbulb.htm
Once you've built it, disconnect the secondary windings of the power transformer, insulate the ends of the wires so they don't short to anything, and temporarily solder a new power cord to the primary of the transformer. Plug it in to the dim-bulb tester, then plug the dim-bulb tester into a power outlet. If the dim-bulb lights at all, the primary winding of your power transformer is internally shorted and you would need a new transformer to continue restoring the 320. This would also explain why the circuit breaker blew when you plugged it in. Otherwise, if the insulation on the old power cord was crumbly, it was probably a short in the old cord, or else the line-to-ground noise filter capacitors C9 and C10 are very leaky or completely shorted. (You should replace C9 and C10 with 0.01 or 0.0047 µF Y-rated safety capacitors: http://www.justradios.com/safetytips.html)

Next use a multimeter to check the RF coils for continuity. It's hard to tell from the photos, but they may have some corrosion that could result in a break in the fine wire used in the windings. They can be rewound if necessary, although that's a challenging job, or sometimes the break is near one of the ends of the winding and you can unwind one turn and splice the break.

Check over the chassis looking for other problems and clean the controls:
https://www.antiqueradio.org/FirstSteps ... ration.htm

Next you'll need to replace all the paper and electrolytic capacitors and, while doing so, check the values of the resistors and replace any resistors which have measured values outside the tolerance range for their specified value in the parts list:
https://www.antiqueradio.org/recap.htm

It would be good if you can find a construction manual for the 320. That would have instructions on what to check before powering it up, and how to diagnose trouble if it doesn't work. But if not, ask here for guidance when you get to that point.

You don't need any test equipment other than a multimeter, your home-built dim bulb tester, and an ordinary AM radio.

If you can repair it, you can use the Eico 320 signal generator to help repair AM and FM radios and to act as a small radio transmitter to send music from your smart phone to a nearby AM radio, as described at the bottom of this web-page:
http://boatanchorpix.x10host.com/SigGenFun.htm

It will be very challenging, but you could repair the 320. You might try fixing something simpler to repair first, like an old All-American Five tube AM radio.

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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jan Fri 26, 2018 5:58 pm 
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Posts: 1684
Location: Sunbury, Ohio 43074
Recall that the opening statement was "I am 19 and have no electrical experience. I am not even quite sure what it's purpose is, but I like it a lot, and want to fix it up rather than sell it if I can find a use for it".

I stand by my suggestion for an isolation transformer as a general purpose safety device. The Variac I suppose is debatable but if the poster wishes to get into this hobby long term, will be required anyway and is a good way to bring a new purchase online without blowing things up.

I do not believe repairing the tuning capacitor is going to be within the means of someone brand new to electronics so I didn't even suggest it :) Possible, yes. Probable, no.

My intent was to help this individual "get started" ... and this is possibly a bit beyond a first project. We're not even sure any soldering experience is in evidence :)

baby steps ........ 3c this time lol

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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jan Fri 26, 2018 7:42 pm 
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Barry, she or he is going to have to test the transformer primary for isolation sooner or later. As a young person, I suspect their funds are limited, and even if not, she or he should limit their investment when starting a hobby that they may not continue. So, substitute some knowledge for funds, and test the transformer now and avoid the expense of an isolation transformer.

As far as tackling a hard project, I was very surprised when I started working with high-school-age people on technical subjects. They are motivated by a challenge. I originally advised them to start small, but they all wanted to try something very hard. Many failed, but they all learned a lot by trying. Some succeeded, and have gone on to do great things in their careers. If I had limited them to only small goals, most would have dropped out.

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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jan Sat 27, 2018 12:28 am 
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Wow everyone, this seems to be an awesome forum! So many answers in 12 hours!

1. I have a little bit of soldering experience and am good enough at it to replace capacitors properly.
2. I already have an Isobar strip with Isolated Filter Banks, but I did NOT use it when it tripped the circuit. Will it work to keep from blowing stuff up?
3. I understand a Variac type device would be ideal, and its something I eventually will buy, just not right now. (College student budget here)
4. As for the Variable Capacitor, it wasn't in pieces when I bought it. After I opened it up, one part fell cleanly off. I think it is fixable, but of course I could be wrong. I'm not sure how exactly to go about straightening it out, but I am good at figuring out how things are supposed to go with some tinkering. (I learned a lot from working on my own car.)
5. I am definitely keeping it, working or not. And I will try to fix it even though I don't currently have anything to test if it is working or not, besides the light bulb on the Eico. It's not something I can devote an entire Saturday to, I will need to work on it in chunks. I am confident with this information I either have what I need or can ask for help!

I will start by reading all the material, manuals, books, etc, then go from there.


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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jan Sat 27, 2018 6:41 am 
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erik530195 wrote:
2. I already have an Isobar strip with Isolated Filter Banks, but I did NOT use it when it tripped the circuit. Will it work to keep from blowing stuff up?

No. It is intended to isolate voltage spikes arriving on the power line from equipment that is plugged into the strip. The kind of isolation we need is where the AC line voltage is no longer referenced to ground. This can only be provided by a correctly-wired transformer. Note that many recently-manufactured "isolation transformers" are not wired correctly for our purposes. Sometimes they can be converted, though.

I tried to find a good thread here on ARF that describes power-line wiring and explains the type of isolation transformer we need and why, but there are too many isolation transformer threads to wade through. This one doesn't discuss the theory, but at least it has a few recommendations on what to buy:
viewtopic.php?f=1&t=291180

erik530195 wrote:
And I will try to fix it even though I don't currently have anything to test if it is working or not, besides the light bulb on the Eico.

Surely you can find someone to lend you an AM radio for a little while, once you get to the point of needing to test the signal generator. Or have they become that rare now?

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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jan Sat 27, 2018 1:43 pm 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 3333
Location: Florida
erik530195 wrote:
........I will start by reading all the material, manuals, books, etc, then go from there.


Don't forget to look up residential ac power distribution.

RRM


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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Feb Thu 01, 2018 5:17 am 
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The moving plates of the variable capacitor must not touch the stationary plates, that is critical.

Yes, hang on to the signal generator, recap it and fix it the the best you can. You can always go back to it after you learn more. Once operational, it is used, as mentioned, to inject signals into a radio under repair, Google 'signal tracing'.
It will also make a dandy AM transmitter, with a simple wire antenna on the output.

Use the 'search' feature here for answers to a 1000 questions.

For test leads, you need to find the correct connectors, not sure if they are BNC or something else. I got mine working by replacing the jacks with RCA sockets.

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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jun Sat 23, 2018 12:28 am 
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With everything else going on this project has been put on hold. But I figured the time has come to figure out whether it's going to be a paperweight or a functioning device.

I have been researching electricity, and radio parts. I understand I need to replace the electrolytic capacitors. (I see them as tiny batteries for different purposes, and as anyone knows old batteries decay and "explode".

Everything seems to be in "MFD" which I understand is the same as uF. The problem is I cannot seem to find the capacitors I need. I am looking on tubesandmore.com (Antique Electronic Supply) and nothing I type in seems to pull up the right thing.

Also, I cannot seem to figure out how many of each to buy. Attached is a schematic but it doesn't seem to give quantities. I wanted to order everything before taking it apart, that way I can replace the capacitors one at a time to ensure no errors. So does anyone know what I am doing wrong, or maybe if I am using the wrong store? I am basically seeing how much it would cost to repair. I'm thinking $35 is the limit with my current budget. (Though I am not opposed to buying or making other equipment like a dim bulb or a power bank since I can use those forever.)

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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jun Sat 23, 2018 12:38 am 
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It appears there are two electrolytic capacitors, although I can't read the schematic.

One of them i all the way at the bottom of the schematic, just to the left of the title block.
The other is all the way at the top of the schematic, below the resistor connecting those two caps.

That is a standard power supply filter circuit.

There is one cap in the parts list, shown as 16mfd or greater. That should be both filter caps.

I expect this is a chassis-mount tubular, possibly having both caps in one package.
Disconnect the wires from the positives of the originals and connect the wires to your new caps.

Connect your new negatives to chassis ground at any convenient point.
The negatives of the originals can remain connected since they're no longer in the circuit.

- Leigh

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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jun Sat 23, 2018 4:16 pm 
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Shouldn't I take the electrolytics out anyway so they don't degrade any further?

Also if thats the case what does "MFD COND." mean? I assumed those were more capacitors. They appear to be the kind that are wrapped in paper, with a few colorful lines on them.

Obviously I am showing my ignorance here but I do want to fix this thing and learn a lot in the process.


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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jun Sat 23, 2018 4:48 pm 
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Location: Sunbury, Ohio 43074
Inexperience is NOT ignorance :) Ignorance would be to not ask questions.

Can you put up a photo of the MFD COND parts? Sounds like they are just paper capacitors, and the MDF (microfarad) COND (condenser) written on them might just be a manufacturer mark.

If they are paper capacitors, they should be replaced. Especially if they are black plastic with colored bands on them.

As for the electrolytics, any further degradation won't affect the operation of the instrument since they are disconnected. If they are not leaking anything now, it is unlikely that they will in the future, but you could remove them if you wish. There may be several ways to do t his .... a photo of what you've got there would help.

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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jun Sat 23, 2018 6:47 pm 
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Everything marked "COND" is paper and should be replaced, also replace the 16 mfd electrolytic.
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Dave


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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jun Sat 23, 2018 6:57 pm 
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easyrider8 wrote:
Everything marked "COND" is paper and should be replaced
C1 is a 50 mmf mica condenser.
It should not be replaced.

- Leigh

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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jun Sat 23, 2018 9:31 pm 
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Location: Sunbury, Ohio 43074
Quote:
Everything marked "COND" is paper and should be replaced

LOL color me "DUH" .... I guess I should sleep before I post here lmao. I was coming off a 12hr drive. Just HAD to get caught up.

For the newcomer ... COND is an abbreviation for "condenser" which is the former name for what we now refer to as "capacitor". Hey, if it were easy, we wouldn't be here.

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 Post subject: Re: EICO 320 Signal Generator Need Help
PostPosted: Jun Sat 23, 2018 9:59 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 9997
Location: Powell River BC Canada
It probably came from a school and might have been put together by
students. The capacitor in photo 3 connected to the black line cord
wire is likely to have caused the circuit breaker to trip by shorting
the hot power line to ground.

The generator originally came with a 2 wire power cord, so if that
capacitor shorted, the whole thing could of electrocuted someone
depending on which way the power plug was put in the wall socket.

We used to call that death by 'Edison Roulette' .

Over the years I have built two of those generators.

Clean and repair it, and you will have something necessary to
test and adjust any home AM radio made in the last 60 years.

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