Constant Radio Noise

I picked up a rare Electro-Voice EV-1180 stereo receiver at an antique store for a bargain and with a problem, constant radio noise. The tuner has three options: phono, FM tuner, and aux. When powered up the FM tuner comes through to the speakers at a constant low volume, no matter what setting the selector switch is on. Would anyone know what is causing this? It seems that something is letting the FM radio signal to pass or bypass the selector switch. Also, the constant radio is accompanied by a typical 60 Hz ground hum.

Any help would be greatly appreciated.

Thanks.
 

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The selector switch is probably defective. Is there a tape out jack? If so, what signal if any appears there? If the switch is defective the "record out" will have the same problem. Too bad there's no tape monitor switch; it's a handsome unit. The hum could be the tuner section only or some other part of the power supply. Capacitors are often bad at that age, especially electrolytics. Diodes are also suspect when hum is present. You should be able to feed a CD player (or whatever) into the Aux input for further testing. It should also produce a signal through the phono input but it will sound funny. Good luck!
 
60 Hz Hum and FM Tuner Noise

Thanks for the reply. The tape out replicates the 60 Hz hum but not the FM tuner, which leads me to believe that I have two separate problems or that the hum and FM tuner are not related.

There are a couple very large electrolytic capacitors in the unit. How would I be able to determine if they are defective? The diodes? Would these components be something that I can trouble-shoot using a multimeter or would I need something more complex such as an oscilloscope?

Thanks
 
Interesting! I wonder if the ground connections to the selector switch are good. Try reheating those solder joints. Also do a general inspection of the input and output connectors to see whether they are properly grounded. Also look for any leaking or swollen electrolytics; those definitely must be replaced.

If you can find a Photofact or service manual that will make it easier; if not, the switching and power supply circuits should be simple enough to trace out.

Diodes are cheap; if it's not too difficult, just replace them. Many people would recommend replacing the electrolytics in any unit this old. By itself, a diode should measure as a low resistance in one direction and an open circuit in the other direction with an ohmmeter. An electrolytic by itself should measure as an open circuit with an ohmmeter. Do all these tests with the power off and the capacitors discharged. Other elements attached to the diodes or caps may confound those measurements. This is where the service manual is really useful.

The filtered section of the power supply should show a steady DC voltage and small AC ripple. A scope is the best way to check this but an AC/DC voltmeter will indicate if they are grossly defective. You will have to check those with the power on so be careful!

Also with the power off, you can use the ohmmeter to check the functioning of the selector switch. With the switch set at AUX and the power off, measure resistance from the Aux input jack to the selector switch output; it should be very low. With the switch in either of the other positions, it should be high.

Good luck and be careful! You might want to cross-post this in the "Solid State" forum.
 
is the radio controllable with the tuning wheel in all modes ?
does the hum change with vol control ?
and does the vol control change the volume ?
do the phono aux lights work correctly ?
 
Thanks guys for the help. Using your advice here is what I found: I tested and inspected all aspects of the on/off/volume knob to which found nothing defective. I traced the RCA aux inputs back to the selector switch O.K. The selector switch doesn't seem defective itself. However, I was able to loosed and turnover the PCB board with large capacitors and small diodes which I believe is used for power conditioning and output, as I noticed its output is connected to the output board with rectifiers. See attached photo. There are two large capacitors marked "Whale 51, +2500UF-25V" and one smaller yet large one marked "Cannon 1000MF 15V" and one small capacitor marked "Minerva 125UF 16V". The board also has four diodes and three resistors. I am going to replace the capacitors. Would you guys have any suggestions where I could buy online quality capacitors?

Also attached below is a diagnostic video showing the problems. Notice that I first turn on the unit but do not turn up any volume. Then I dial in a couple radio stations and then operate the three way selector switch through which the FM tuner signal can be heard across all three modes, "phono, tuner, aux."

To answer your question Pete, respectively: The radio is controllable in all modes. The hum does not change by volume control. The volume know does control loudness; when turned up it overtakes the problem signal and begins to operate normally (see video). Lastly, the lights work correctly.
 
All,

Thanks for the replies. After replacing the electrolytic capacitors on the power conditioning side, the 60hz buzz disappeared. And the FM tuner signal quieted. However, it is still softly present and now I'm dealing with a crackle and fuzz sound, like that of a spinning vinyl record. Any suggestions? The transistors? There are a couple other caps in the unit but they appear to be o.k.

Thanks.
 
Could it be poor shielding.. ?

Sounds like a shielding issue.. :scratch2:

If the unit is that old, there may be a power lead or wire running pass a signal wire and the leakage is causing a drop in the current.

Grant it... this would have to be a substantially "hi-current" wire.

I would check everything on the hi-end that is routed pass "signal wires/wiring".

Now.. :yes: you can make a shield out of cardboard and aluminum foil, insert this between suspect locations, and listen for a drop in the "hum".
This location would be your suspect "bleed zone".

:nono:However be very careful not to become the conductor for solder points or fuse tabs! Nor should you ground yourself to the chassis or other electrical points. Insulate.. insulate... Insulate!

By replacing the suspect wires or shielding the zone, you might eliminate the issue.

This is of course..... :scratch2: If it is a shielding issue to begin with.. ?
 
You can find service manuals for the EV-1181 on line for less than 20 bucks, I just got one. (See http://www.ebay.com/itm/Electro-Voi...st-/380722650137?_trksid=p2141725.m3641.l6368, for example.) Oddly, your unit looks different from mine. It would be difficult to scan and upload the manual because the schematics are fold-out pages.

I have a working channel and a noisy channel with a very faint signal. The aux output is fine, I found a blow-out transistor on the power amp board, replaced it, but it is still not working properly, and the replacement transistor runs hot. Haven't had time to work on it for a few days, but I have some ideas to pursue. I'm not sure why I'm doing it, I guess it is the challenge of finding a solution.

If the layout of your receiver is similar, Electro Voice used circuit boards that made contact with vertical pins on a large "mother board". These pins and contacts need to be clean, and the contacts need to be tightened which you can do with a small screw driver. Before I did this, nothing much worked, afterwards only one channel was bad.
 
At that age I would just replace the power supply filter caps rather than trying to test them. You can test them with a multimeter with cap test function, but it will only give you the uf, and there are other parameters like ESR that need a special meter. The ones you mentioned seem to have pretty low uf for power supply filters, but I'm not clear that these are the only electrolytics in the set.

Mouser.com is great for parts once you get the hang of their database engine. Get good quality like Nichicon, Rubycon, Panasonic and avoid no-names or Who Flung Poo Capacitor Factory #2. It's worth a few cents.

The selector switch may look OK but it may have leakage or a short between sections. If someone tried to clean it with spray tuner cleaner, for example, it may have soaked into the phenolic board, making it slightly conductive. You could disconnect the tuner input to this switch and see if the problem disappears. If so, it's the switch.
 
At that age I would just replace the power supply filter caps rather than trying to test them. You can test them with a multimeter with cap test function, but it will only give you the uf, and there are other parameters like ESR that need a special meter. The ones you mentioned seem to have pretty low uf for power supply filters, but I'm not clear that these are the only electrolytics in the set.

Mouser.com is great for parts once you get the hang of their database engine. Get good quality like Nichicon, Rubycon, Panasonic and avoid no-names or Who Flung Poo Capacitor Factory #2. It's worth a few cents.

The selector switch may look OK but it may have leakage or a short between sections. If someone tried to clean it with spray tuner cleaner, for example, it may have soaked into the phenolic board, making it slightly conductive. You could disconnect the tuner input to this switch and see if the problem disappears. If so, it's the switch.

I found another bad transistor, and replaced it, and both channels work now. I replaced the power supply filter cap and the electrolytics on the power amp, but there is still a little hum left--not too bad, but not quiet enough. When I get a chance, I'll wire some more caps in parallel with the power supply to see if it helps. I'll also bypass the the selector switch as suggested.

It's probably not a unit worth all this effort, but it is an interesting challenge. Thanks to everyone for the suggestions.
 
Is it possible there are other caps (not necessarily on the power supply board) that have gone bad and need to be replaced? Seems like it should not have an intolerable level of hum when it's working up to spec.

There is probably a plethora of hum tracing threads in Solid State, you might find some other things to check. I'm just the blind leading the blind.
 
I replaced all the electrolytics on the tone/volume control board plus all the electrolytics on a multiplex board. This fixed other problems (better sounding FM, and no more scratchy volume control), but still the hum. I'll check the solid state section as suggested. I should work on something more important than this receiver!
 
FM bleed problem fixed?

I get the same thing if I forget to turn off my Magnum antenna amplfier. Not surprising, as I have a rather large antenna on the roof. Turn off the amp, and it goes away.

In your case, sounds like it's just a local station overpowering your unit's rejection. Not sure what you could do to block that other than using a tunable FM trap on the antenna connections.
 
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