JVC RK-450 Receiver Won't Power Up

[brakeshoe87]

Thanks in advance for reading this long post by a non-audiophile newbie.
I recently tried to turn on my stereo for the first time in several months and experienced problems. The speakers were not on, but it powered up. When I checked the speaker connections and retried it, the receiver stopped working. It had previously been in pristine condition. Since there was no fuse on the back panel I looked elsewhere for issues.

The speakers are EPI 100’s from the 70’s (again, I am not an audiophile). As far as I know they were fine before this chain of events, but I don’t know how to confirm that. When I took of the speaker covers I saw that the woofers were askew and the foam that surrounds them was in pieces. Again, I don't know if this was old age or some sort of traumatic event that also damaged the receiver. There are kids in the house.

My first goal is to determine if the receiver is salvageable. Can anyone point me to whether there are fuses I can check and potentially replace? Secondly, I want to evaluate the speakers. I see kits for replacement foam are available for these speakers, but I don't know how to tell if the cones themselves are still viable. Any suggestions will be appreciated.

 

[Tom B]

As far as with the speakers, it is common for the foam to decompose, but not the damage you have. There is a voice coil mounted on the cone, behind the dust cap, that goes into the circular opening of the magnet assembly. This coil is supported by the cone, as well as a laquered circular cloth called a "spider" which is secured to the metal frame of the speaker carriage. When to foam surrounds decompose and go bad, the cone usually stays in position. From the looks of your speaker, either the coil broke free from the cone, or the spider has come loose from the frame (not common). The tensile foil leads may have come loose as well. If the coil is shorted, or the leads are touching the frame, it could show as a shorted speaker and keep the receiver from coming out of protection. Check the speaker connection on the receiver without speaker connected. (check and make sure there is no DC voltage on the output terminals. Test the receiver with a pair of headphones is the speaker terminals don't have any DC voltage (should be less than 50mv)
If the speaker voice coil is intact and still viable, it would need to be positioned properly, and secured to the spider and cone, as well as new foam surrounds being installed. This project should be done by someone familiar with this kind of repair.

 

[brakeshoe87]

/I looked through the videos at part express and did not see anything that looked like it related to testing speakers. I didn't see a search option, but paged through many pages of instructions on building speakers. Could you post a link to the video you are suggesting i look at? Also in case you didn't catch it in the title, my receiver is a JVC RK-450.

 

[slimecity]

OMG - I have never seen a speaker looking like that! Incredible.

What is being suggested above is that you get hold of a digital meter, put it on mV setting - and test the speaker terminals of your unit with power on and the correct speaker output selected. Do you usually hear a "click" when the unit powers on - are you still hearing that?

If your haemorrhaged speaker is looking like that, the coil may have shorted, shorting out your unit's outputs - as Tom B has said above.

Are you able to get a meter and take these readings? You don't actually need anything too fancy, something like this would do for these purposes:

https://www.parts-express.com/3-1-2-digit-19-range-digital-multimeter-with-transistor-test--390-500

 

[brakeshoe87]

I tried to do a little more debugging and here is what I can report:

• There is no obvious damage to the speaker other than the decomposed foam. Wires aren't touching, spiders are still attached to housing, but the speaker is not affixed to the center unit down towards the magnet
• Attaching a 9V battery to the speakers produces an audible click
• I used a small Sears multimeter set to Resistance/Ohms and got no reading when attaching it to the speakers rear terminals or directly to the wires going in to the speaker
• I have disconnected all wires from the receiver and still do not get any sounds or lights when pressing power, my next step there is to open it up and try and see if there are any newbie serviceable fuses I can verify as fried and replace

If I missed anything or anyone has more suggestions please let me know. At this point I am pretty much resigned to buying new speakers, but am engaged enough that I would like to try and track down what happened. My best guess is a bad connection on the speaker wires shorted out the unit when I had the receiver on and moved a speaker to see if it was connected.