JVC RC 838 plays wonky tapes

I got a supposedly perfectly working radio on eBay. This JVC functions great except the cassette player. Rewind and fast forward work good. About 1 of 10 tapes will play fine (the tapes are good on all other boomboxes). The other 90% of the time the tapes start to sound as if they are being eaten. The volume also goes way lower. If I push stop or rewind etc then play again it will play fine for a couple seconds before it happens again. Here is a link to a video. Any help would be greatly appreciated.
https://youtu.be/oOfXckLYz-Y

I would clean and demagnetize tape head and try to adjust azimuth.

Thanks bill. Will try that when I get home. I have a tape demagnetizer but not sure how to adjust the azimuth.

I would suggest cleaning the the capstan idler tire/wheel too. Over time, the idler tire/wheel becomes shiny and slick from oxidation. Cleaning usually brings a bit of grip back to them. If cleaning the heads, demagnetizing the heads, and cleaning the idler wheel doesn't seem to help, you are most likely looking at worn out belts.

donahuest said:

Thanks bill. Will try that when I get home. I have a tape demagnetizer but not sure how to adjust the azimuth.

Click to expand...

You have to adjust the screw on tape head

Do you adjust both screws or just one? Also I have a cassette tape head demagnetizer, just wondering how long you are supposed to leave the tape in play before stopping? Thanks. I’ll start with a good clean

Those electronic demagnetizers work fast so you only need to use it for a moment. Just clean the heads really well & demagnetize it. I don’t suggest you mess with the azimuth settings if they weren’t tampered with before. It is set at the factory and shouldn’t change unless someone tinkered with those screws. You can tell if they were worked on because the screws will have been painted with a fingernail-polish like setting compound, often green color when it was factory adjusted. But if you do mess with them, only adjust the one that is spring loaded. And by the way, the service manual for this product says to use a dual channel oscilloscope & a test tape for proper azimuth alignment. Some people are going to tell you to “listen” but if that’s all you need to do for proper adjustment, then this (and 95%) of all service manuals and the factory are wrong then.

Thanks Superduper. Yes I only ran the demagnetizer take for a few seconds but wasn’t sure Because when I run it on my pioneer cassette deck the light on the demagnetizer tape goes out after 2 or 3 seconds indicating its done but on the boombox the light stays on(for at least 10 seconds cause gats when I hit stop). Can you overdemagnetize and harm the radio? I’ll try cleaning a bit better and see if I get some improvement. Thanks again everyone !!

The light goes off in your pioneer deck because that deck has an autostop feature, which stops the deck when it senses that the tape in the cassette deck is no longer moving. On your boombox, either it doesn't have an autostop feature, or it is not working properly, which is why it doesn't stop. There is no actual tape in those demagnetizers unlike a real cassette where the trailing supply reel follows the drive take-up reel (tape gets pulled from supply). So the supply reel on a cassette deck will not spin which normally means that the tape is done, and since there's no tape in a demagnetizer, the supply reel obviously will not spin. This tells the deck that the tape has reached the end, and it should stop.

Here is some operating instructions which should apply for most all of these cassette cartridge type demagnetizers.

BTW, remember to follow fatdogs instruction regarding cleaning the capstan needle and pinch roller.

Thanks for the reply. I cleaned the capstan and head with alcohol and demagnetized it. I cleaned the pinch rollers with a dry swan (so not great) because I’m never sure wether alcohol or water will hurt it? It will play the odd cassette fine then sound like it’s eating the rest but it doesn’t actually eat it just sounds like it.

sounds like you need a new pinch roller

Personally if you are planning to keep and use deck it should be fully restored. New belts and pinch roller. Cleaned and fresh grease. Cleaned and demagnetized heads. I prefer using a wand type deck demagnetizer as unit doesn’t need to be powered on. Also do not keep any tapes in room while demagnetizing as it can ruin tape

Yes definitely going to keep this one. It sounds great with radio and line in. Even the odd cassette (about 25%of them) will play great all the way through (although automatic stop might engage a couple times). Plus I already bought a sweet strap from blu_fuz! I’ve already got a pioneer sk700 opened up I have been neglecting and a couple Hitachi’s on deck. I would love to bring this and my Clairtone in to somebody who knows what they’re doing but here in Canada repair techs seem to be like unicorns, hard to find. If anybody knows a good one near London Ontario please let me know. I’d even be willing to drive the couple hours to Toronto.

BTW thanks again for your responses. I should learn my lesson and stop buying “flawless” boomboxes on eBay that always seem to “break in transit”. The best boombox I ever got was off this site from baddboybill. A sharp vz 2000!

I thought your boombox had properly working belts, but now, I think you simply need a full service, which includes new belts and proper cleaning, and yes, definitely clean the pinch roller with isopropyl, the strongest ones you can get (100% vs 70%). Sometimes, the roller even needs to be lightly sanded to bring out a fresh surface if highly oxidized or hardened, but replacement is the best. You only have a few units so the cost is well worth it. For those folks who have scores, even hundreds of boomboxes, it's probably not worth it to do that to all their units. it simply sounds like your tapes are slipping, some worse than others probably because of the friction coefficient of the tapes vary, or because longer tapes are more difficult to pull than shorter tapes. I've seen tapes from goodwill have so much friction that they don't play at all. Press play and the friction of the tape sandwiched between the head and felt pad beneath the tape stops it dead cold.

As for your experience, you need to understand that if you are going to be buying 40 year old electronics, especially those with mechanical parts such as cassettes, these sets definitely require periodic maintenance to run their best. Even if a unit is advertised as "all-working", it doesn't necessarily mean "perfectly-working" since it begins to deteriorate the moment it leaves the factory. Your best bet when buying units that are "all working" are to see if the seller advertises specifically and exactly if and what has been done to it. If it says belts changed, then at least you know that the belts are new, but it doesn't say if it had proper cleaning, pinch roller refresh, lubrication, etc. Also, does it say controls were cleaned? If not, you can almost expect a certain amount of static in the controls when operated.