Panasonic RX-5500 Tape and background noise help needed

[doug2112]

Hi everyone,

I have a friend who is a musician in Dallas and uses a boombox in his act sometimes. My wife bought a Panasonic RX-5500 and took it to a local shop to have it serviced. They charged a ton for rush service and apparently only replaced the belt on the tape drive and left a ground unhooked. I used to work on copiers, but was hesitant to work on an antique boombox with no schematics--I have no idea where to source parts, etc.

However, the shop that did the repair pulled the "we only replaced the belt, anything else is your problem" when I tried to approach them about the noise that I figured was a loose ground (and it was--they left the ground off of the tape assembly when they worked on it!).

So, the problems I am having now are background noise and the tape player doesn't play at a consistent speed. I'm guessing it needs a new tape drive motor for the speed issue, but don't know enough about sound to know where the background hum would come from--if it isn't more grounding issues.

Does anyone have a parts list for the 5500 and/or a source for parts? I figure if I can fix the tape speed, I can figure out the background noise....unless someone has an idea for me!

Thanks,

Doug

 

[Superduper]

If a ground was unhooked, you wouldn't get background noise, you would get a very noticeable and objectionable hum. You said the shop "serviced" the boombox, is that what you requested, or did you specifically request for a belt change? I suggest you get the heads cleaned and demagnetized first. This could improve the sound somewhat and is non-invasive if you use the cassette type of demagnetizer (it looks like a cassette tape). Another thing that could improve the sound is if the head azimuth is off, you can readjust it but could also make it worse by screwing around with it. Other than that, you may need to get the record/playback switch cleaned. A dirty switch could certainly introduce hum into the circuit and is directly related to the tape circuits. This service isn't particularly hard, all you do is inject deoxidizing electronics cleaner inside that switch and work it back/forth about 50 times to scrub off any oxidation. The only thing is that this service can't be performed without opening up the set. I would hope that the "shop" did this for you as part of their "service", but then again, I don't know what your shop actually did. If they really only did the belt, this seems like bad practice because this is a recipe for come-backs, which leads to unhappy customers and bad reputations. Anyhow, if these measures don't adequately address your S/N ratio issues, then this could be a circuitry issue and unfortunately, is usually beyond the scope of the casual hobbyist to repair. There might be a service manual here in the archives, but if there isn't or the quality is inadequate, you can buy one HERE. The service manual can be useful in figuring out how to disassemble the unit, and illustrate the location of the record/playback switch. Lastly, do you know for sure that the hiss or background noise is due to the unit circuitry and not in the tape cartridge? As for the speed, if the tape deck has not been used in a very long time, all the moving parts could be lacking lubrication. I would think lubrication where necessary would be added during a deck service, but if they didn't, it might be beneficial if you just exercise the deck for awhile to get stiff grease to loosen back up through usage.

 

[hopey]

This can happen with poor insulation in the Tape Head cable and termination. This can be be disturbed when the box gets pulled down. It is a ground loop as the cable is shielded. The fix can be as simple as de-solder the cable from the head and spread the conductors and solder back on. You may have to do this both ends.