Nordmende RK 4186 (aka JVC RC 838)

[Arbusto67]

Hi guys, few days ago I acquired the boombox in the title from eBay (slovenian seller), posted here because all uf us know that this Nordmende in an aka of the JVC RC 838, even if in a more luxury flavor because the RK 4186 has 6 FM presets (which the JVC does not) and the service manual states it works at 15V (12V for the JVC), so it's more powerful. The unit powers up but the radio doesn't work, I even tried the DIN input but got no sound; playing with the source selector I discovered that moving it slightly from the "radio" position I was able to receive some stations but obviously it's not the correct way to say if the radio could work correctly. Immediately thought that the cause of the radio malfunction was oxidization, so opened the unit and, after removing spider webs and every sort of dead small animals (!) that were inside I tried spraying the source switch multiple times with deoxidizer, unfortunately to no avail even after many dozen movements of the switch itself. Tried even the cassette deck but the motor doesn't seem to be working, I have to clean and investigate further. The boombox is very nice and in good condition (save for the 2 antennas, one missing and the other one broken, but I noticed 2 suitable ones on Aliexpress for little money), so I would like to fix it, maybe one of you has the equivalent JVC model and has already faced this kind of problems. Do you think that source switch oxidization is the cause of the malfunction or should I search for something else?
Thank you very much for every help.

 

[hopey]

It's a hard one to pin point it could be capacitors that would work for a little bit then drop out. I have had success with radio boards by washing down with isopropyl alcohol then drying with a small fan heater. Also there can be a small ferrite plug near the variable capacitor that can be unscrewed removed and cleaned also the inside contacts. The radio signal can be weak by high resistant joints so remove and clean all contacts with fine grade sandpaper and the grease.

 

[dubout]

Did you play around with the preset wheels? Also what about AM reception or any other band, any signal there? Not of big help but trying to help circle the problem. Is only FM, is it the tuner dial or maybe the connection to the board ...

 

[Arbusto67]

Thank you for your suggestions; I tried even the presets but the behaviour is the same, no reception. The other bands work only when you tinker with the source switch, finding a sweet spot, like in FM. In the meantime I discovered that the deck motor is actually working when powered directly with an external power supply, so maybe a contact doesn't engage when it should or something, I'll investigate. Another very odd thing that I found is that when selecting the source "tape" with play engaged, checking the battery voltage with the embedded gauge it goes full scale (which seems pretty obvious using AC), a bit more than half scale in "DIN in" and "turntable" and finally a lot less than half scale in "radio" position, so it's like there is not enough voltage for the device to work properly in all the switch positions, save for "tape", which even corresponds to the off position if you don't play a tape. The adventure goes on...

 

[dubout]

Maybe you are onto something there! Maybe the half-engaged switch produces a short that gives more power and therefore enhances reception. Good luck!

 

[Arbusto67]

I think I'm going out of luck unfortunately... I removed the source switch from the board, dismantled it and cleaned every contact (it was dirty but I think the contact cleaner did a fairily good job actually because the areas where the sliding contacts move were clean), reassembled and resoldered it to the board but everything is as before. Well, sometimes this hobby is very frustrating, a lot of work for nothing. Maybe there's a defective component on the tuner board, not easy to find out, I think I'll follow hopey's suggestion to clean the board with alcohol and see what happens, even if it looks relatively clean.

 

[Arbusto67]

Cleaned the tuner board with alcohol, no difference, even checked the board for bad solders but all of them seem good to me. Noticed that disconnecting the tuner board from the main one the voltage reading from the embedded gauge is equivalent to the one in the other source positions, so maybe the problem really resides in the tuner. Don't know what else to search for, I'm a bit discouraged because testing all of the components would take a ton of time, not easy to find.

 

[hopey]

Can you take a photo of the tuner board it may have these ferrite plugs that can be serviced.

 

[Arbusto67]

Well, you can believe me or not, taking the last look at the tuner board I noticed a very small blob, dark brown colour (maybe old flux), between two contacts of a connector, scraped it off with a toothpick and cleaned with a brush, connected the tuner to the device and, almost for fun, turned on the boombox and IT WORKED!
Now all the sources give full scale in the battery test! Don't know if the only cause was that brown stain but I did it! Tomorrow I will post a picture of the Nordmende, it's not perfect but it looks nice. Thanks guys to all of you for the help and support, really appreciated.

 

[Arbusto67]

Here it is. It needs a couple new antennas but It's working completely, even if I cannot seem to be able to play an external source connected to the DIN socket, even selecting "DIN in". It seems an odd behaviour to me, do some of you guys have the JVC equivalent and knows if it behaves the same?

 

[hopey]

With Din you can play around with the pin out to find the correct polarity. Get yourself a cable and strip the end and connect to your input swap the wires until you get it working. You may have to press play and record to active line in.

 

[dubout]

I have a Discocorder, too and can try it out. In the mean time try what hopey says: activate record and see if that solves the problem.

 

[Arbusto67]

Yeah, I know that activating record always should work but I don't think that a "DIN in" position of the source selector is needed in order to do so, didn't try it out yet anyway. Another thing that I noticed is that when recording both of the meter gauges only work when selecting automatic level, if you select manual level only the left one works, tried deoxidizing the switch that toggles between the two modes but didn't work. All of the pots, including manual recording level, have been deoxidized already. Go figure...

 

[dubout]

I tried it out. MP3 through DIN, selector put to DIN in an press record on the cassette. Worked.

 

[Arbusto67]

Thanks mate, much appreciated help.