tardpie - 2010-05-09 11:39
hello all,
I believe my beloved JVC RC-M70 may need a new transformer. Are there any aftermarket ones available, or am I going to have to find a "parts" m70?
The problem: Radio works, line in works, cassette does not work, and the unit will not run off of batteries (power light & dial light also not functioning, even when the box is on). I have a feeling that one day, while plugged into the wall, I got a power surge through the socket, and that ruined something inside the box. Its not a belt issue or anything like that with the cassette deck.
So, any tips or suggestions are welcome. Or even if anyone around here does repairs... I have the service manual.
Doubt it the transformer, it maybe a blown regulator or fuse, which may have been cause by bad capacitors, the unit is over 20yrs old, if you are going to use it daily or alot, you have to recap it, doesn't matter if it working good at the time, capacitors only last 10yrs or 2000 hrs of operation, by using it without restoring it problems are going to get worst and you will end up blowing the transformer,voltage regulator and much more.
Not trying to be harsh, been seeing alot of people use these classic valuable boxs without restoring it, thinking all they have to do is change the belts!! No you have to recap these even if the cap may seem good, it a matter of time before they will fail.
No, that's cool, thanks for the tips!
So, where do I go to get new capacitors?
You're clearly fishing Salavatin Army because how you came to conclude that it may need a transformer is beyond me as it's not even related to the symptoms you are describing. You say the deck is not working but then you say it's not a belt issue. How do you know? Because belts are the number one most common cause of that. Also, it may be your motor is blown. Re-capping the box is always a good idea and may improve the sound and reliability but I doubt it will fix the issues you are describing. Tuning dial lamp not working? Bulb probably burned out. Works on AC but not batteries? -- possibly corroded battery contacts or solder joints to the contacts or the AC/BATT switch in the AC socket is bad or needs oxidation cleaned off.
Just don't fall into the trap and assume that there is one simple cause for all your issues. More than likely, you are having multiple issues with your boombox.
Best if you fix it yourself. If you need someone to fix it for you, and you are having multiple issues it could get quite expensive. If your boombox is in great cosmetic condition or has sentimental value, then go for it. Otherwise, the cost to repair your boombox could easily exceed it's value.
Give me some more specific details about your cassette issue and maybe I can help point you in the right direction.
The last tech that worked on my M70 was not able to diagnose the problem, even with the service manual. When I picked it up from him, he suggested it might be a transformer problem.
I know its not a belt issue because I've looked inside at the belts. Perhaps its the motor.
The box was literally working just fine one day, and a day later, when i went back to turn it on, there was no dial light, no power light, and absolutely no response from the tape deck. However, the radio part still worked. The box had not even been moved. It was just plugged into the wall the whole time. That's why I think a surge of power came through the line & blew something up inside. I dont see how all these multiple issues could strike so suddenly, all at once.
It's a blown voltage regulator the dail lights and the tapedeck motor run on the same circuit, on that box. But only way to know for sure is to have someone look at it, a good repair tech can fix it for you.
DrMR2000 is right. I just looked at my Service Manual and your M70 has 3 voltage regulators -- X503, X504, and X505. They are 7.5v, 10.5v and 12.0 volt regulators. Your cassette motor and dial lamp and power LED runs off the X505 regulated rail.
Each regulator is comprised of a transistor (X505) a zener diode (D505) and an electrolytic capacitor coupling the base and emitter of the transistor to ground. Either the transistor or zener diode could have failed. Also make sure the capacitors are not shorted to ground or the transistor will either not turn on or output grounded (if emitter cap is shorted) but if that were the case, the transistor is almost surely toast too.
I wish all my repairs would be this easy. If your tech couldn't fix this and actually suggested the transformer, I don't think you should bring it back to him. The most power hungry module in your boombox is your amplifier when cranked up. Since it runs off the 15v rail and not the regulated rails, I presume that the radio rocks, right? With that, it should've been a telltale sign that the transformer was working right.
Fire your tech and get it fixed. Replacing the X505 and D505 will almost 95% certainly to bring it back to life. While it's open, an extra buck or two to replace C526 and C517 basically eliminates all likely culprits.
And if you REALLY REALLY want an M70 transformer, I'll be happy to sell you one, but it won't fix your particular problem. Good luck.
Well thank you, DrMR2000 and Stormin Normin!
Now which one of you wants to replace the voltage regulators on my m70?
I don't know of any other local techs, unfortunately.
Wow! Sometimes I read the tech stuff just so I realize how little I know! Great diagnostic work by DRmR and Stormin!I love the M70 and I collect them, so this is even better for me!
quote:
Originally posted by Salavatin'Army:
Well thank you, DrMR2000 and Stormin Normin!
Now which one of you wants to replace the voltage regulators on my m70?
I don't know of any other local techs, unfortunately.
I'm 3,000 miles away in California.
That adds quite a bit of cost to you so a local service might end up being cheaper. If you really can't find someone local to do this and you're willing to ship it to effect the repair, PM me.
My local electronics supply store said I "don't have the right numbers" when I went in asking for an X505 transistor and D505 Zener diode. They were able to find a C517, but that's it.
That just the service Manuel part located number you need to look at the regulator and write that number down. The shop sure know that already, go to a different shop.
