Fisher PH-D715 DC Voltage on Speaker output

[stereomann]

Hi
i bought a Fisher Boombox on ebay
the seller thought it did not power up

but when i got it it does power on
the radio works on it, cassette needs new belts, cd player needs work.
when i played it in my garage i thought both speakers were working but i did not play it for long and left it out there for a few days.

today i took it apart and blew the dust out of it and took it down my basement to work on it. but when i hooked up both speakers
i noticed one of them sounded blown. So i hooked the good speaker to that side and it sounded fine. but i checked the dc volts and it had 7v on it
I'm not sure if that's normal or not. but i had a parts one i bought yrs ago and that one has 6.6 volts on both sides.

so the good thing it i do have 2 extra speakers. from the parts one but will that voltage damage them.

 

[hopey]

It's actually really hard to measure volts and current in the speaker circuit as it fluctuates are you seeing ac or dc?

 

[Superduper]

How did you measure DC voltage? There should be almost zero. If any, should be only in low millivolts. And what model? And yes, if you truly have DC in the speaker outputs, you will damage the speakers but you have bigger problems than that as the amp or other circuits have definitely failed.

 

[stereomann]

I just hooked my meter to the speaker terminals and put it on dc volts

the weird thing is that i took the speaker apart last night and moved it back and forth a few times and put it back together and it doesn't sound blown now. and when i tested the ohms of the speaker it was 3.5 and that was before i did anything to it. and on the back of the magnet it says 3.2 ohms.

maybe something happened to the speaker in shipping and that fixed it.
the radio sounds fine so i don't know if i should just leave it be
maybe a cap is bad in it somewhere?

even the other one i bought yrs ago has voltage on it too.

 

[Superduper]

Some variation in resistance reading from marked to actual is perfectly fine as speakers are rated in ohms of impedance whereas with a meter, you are measuring DC ohms which isn’t the same. However, once again, any DC, especially anything over about 100mv would be highly concerning. I doubt you are reading over 7v DC in the speaker outputs, your speaker coils will cook very quickly. This doesn’t look like an auto ranging DMM. Are you sure you aren’t in the mV range? Anyway I don’t have a schematic for your system to look at but I can’t believe voltage there would be normal.

 

[stereomann]

no that meter is not auto ranging it has settings for 2, 20 or 200v DC i put it on 20

it seems kind of weird to me too that voltage would be on the speaker outputs.
but it still works so i don't know. would it have sound at the outputs at all with that kind of voltage on it?

i did clean the controls of the volume and EQ sliders
so maybe that could have made a difference with the distortion also.
but i did try the speaker that was working before cleaning it and it sounded fine on both channels.

it don't make much sense to me that the other speaker is working correctly again now after just taking it out and moving the cone a few times.

maybe if someone has another Fisher PH-D715 or maybe a similar model they can test the speaker outputs and see what they get to confirm it.
it would be less work trying to figure out if something might not even wrong with it.