JVC M90 Radio tuner issue

[Tracerec]

I could use some advice on repairing the tuner section of my M90. Problem is I can dial in to one station but all the others are distorted. I had in to a technician who originally diagnosed the problem as needing a ferrite tuning slug on the oscillator. I obtained a slug from a member here a few years ago but that didn't fix the problem. In the word of the tech who looked at: The local oscillator is not tracking properly and is drifting off frequency so you end up getting over modulation when turning in to a station. He can tune it in to either a station on the low end or high end of the band but not the whole FM band. Unfortunately they are one of the few remaining shops in my town and are extremely busy. Meaning they don't have the time for it. I was hoping someone here might have seen this before and could help with a solution.
Cheers,
Dan

 

[hopey]

I've had success in recovering tuners by dowsing in isopropyl alcohol and scrub with a small paint brush. Then dry it out with a small fan heat for an hour.

 

[Tracerec]

Thanks Hopey. Unfortunately the board has been thoroughly cleaned albeit I don't know what they used but it was done at a reputable repair shop.

 

[Superduper]

oscillator drift is most likely due to incorrect regulated supply voltage or aging components whose values are drifting (or drifted too far from specs). Or a bad crystal. Unfortunately, this is not a DIY type fix. If your technician is uninterested in putting in the time to repair this, you are better served by going to a different technician, and you'd need to impress upon them that this boombox is very important to you. Generally speaking, many repair shops are unaware of the value of these boomboxes and automatically think they are "not economical" to repair. In other words, they believe that the cost to repair the item exceeds the value and they worry that they won't get paid for the repair because the owner may abandon the radio.

BTW you did not mention whether this affects only FM, or if it affects the other bands as well. IF we are talking local oscillator here, be advised that the FM band has it's own local oscillator and the MW band has a separate one. If the issue you have is common to more than FM, you may have a different issue besides just the oscillator.

 

[hopey]

Why did your tech provide you with detailed information yet couldn't fix it? Probably because they didn't have the knowledge or confidence so risk was two high handing you back a dead radio. I would go back to the drawing board.

 

[Tracerec]

oscillator drift is most likely due to incorrect regulated supply voltage or aging components whose values are drifting (or drifted too far from specs). Or a bad crystal. Unfortunately, this is not a DIY type fix. If your technician is uninterested in putting in the time to repair this, you are better served by going to a different technician, and you'd need to impress upon them that this boombox is very important to you. Generally speaking, many repair shops are unaware of the value of these boomboxes and automatically think they are "not economical" to repair. In other words, they believe that the cost to repair the item exceeds the value and they worry that they won't get paid for the repair because the owner may abandon the radio.

BTW you did not mention whether this affects only FM, or if it affects the other bands as well. IF we are talking local oscillator here, be advised that the FM band has it's own local oscillator and the MW band has a separate one. If the issue you have is common to more than FM, you may have a different issue besides just the oscillator.

Hi Superduper,
Thank you for your reply. The problem is limited to the FM band.
You are right; they are incredibly busy and likely see far more value in repairing a Krell amplifier than spending a lot of bench time on my radio. I've gone to them for many years and they have always been professional and competent. They've been around since the 1960s. I will give him a call and impress upon him the personal value of my M90 and see where that takes me. I'll let you know what he says.

 

[Tracerec]

Why did your tech provide you with detailed information yet couldn't fix it? Probably because they didn't have the knowledge or confidence so risk was two high handing you back a dead radio. I would go back to the drawing board.

Hi Hopey,
Thanks for the response. I'm a long time customer and asked him what he had done so it would give me something to base my research on. They didn't really diagnose the actual problem or they would have fixed it. I think it comes down to bench time is valuable and they didn't see the value in putting too much time on it.

 

[Bigpopa64]

Hi Hopey,
Thanks for the response. I'm a long time customer and asked him what he had done so it would give me something to base my research on. They didn't really diagnose the actual problem or they would have fixed it. I think it comes down to bench time is valuable and they didn't see the value in putting too much time on it.

Send it to Teddy Hashee if he can't ficmx it it cannot be fixed

 

[Radio raheem]

Same applies to the honourable Superduper....he has fixed dozens of radios on here over the years, if he couldn't fix diagnose the problem nobody else can

 

[hopey]

give this a go:

The OSC. VAR. Conductor can corrode internally, to fix you fully unscrew the ferrite plug. Inside there are two pins one each side which can be cleaned with fine grade sand paper, clean the plug with alcohol. This has a sort of polarity and when screwed back in the signal will come and go as the plug is screwed further down. You can calibrate by setting the tuner to a known station and make it match the Freq indicator. It's a bit of trial and error but pretty easy.

I bet the reason is the high resistance on the OSC. VAR. Conductor between pins.

 

[Tracerec]

give this a go:

The OSC. VAR. Conductor can corrode internally, to fix you fully unscrew the ferrite plug. Inside there are two pins one each side which can be cleaned with fine grade sand paper, clean the plug with alcohol. This has a sort of polarity and when screwed back in the signal will come and go as the plug is screwed further down. You can calibrate by setting the tuner to a known station and make it match the Freq indicator. It's a bit of trial and error but pretty easy.

I bet the reason is the high resistance on the OSC. VAR. Conductor between pins.

Thanks Hopey,
My apologies for the late response. I had a bit of health crisis that sidelined me for months but I'm much better now. The ferrite plug had been replaced by the tech but I don't know if the pins were cleaned or not. Worth a try for sure! I got the JVC back from the shop with no charge. I'm going to contact Teddy and Superduper to see if either of them will help me out. Cheers.