PC-V66 Digital Tuner Station Presets wiped with power cycle

[jratz2k]

Hi, Newb here in the boomboxery. I had located a couple others post this same issue with their JVC PC-V66 sub wolfer boom box with no solution. I have had this one since new. Always liked the combo of a digital tuner, great sound, AND an aux input... originally for a cd-player and now a bluetooth dongle or iphone adapter.

Anyway, for many years now the feature that has died is the ability to remember radio presets. It used to work but for a while now when you shut off the main power, it forgets the stations and it returns to default. Very specifically, this mean even when I just shut it off with the main power button if forgets... even when I don't unplug the unit entirely.

I have some access to salvaged replacement boards for this unit but I'm not a skilled enough circuit person to determine if its a latent power issue OR and issue with tuner board or how the design of this storage of radio stations works.

I found a service manual free online for the UK version... I'm in the USA so I hope it's close enough. Hopeful somebody smarter than me can determine if there is a capacitor providing this power that has failed, some EEPROM, or at least help me decide if a replacement digital tuner board is worth the hassle..? Hard to know if the replacement board has the same defect as it is used as well. Else I'll just deal with it. I can pick these up and just replace the whole unit but this seems like a defect that appears in these units.

Thanks for any assistance. I've attached the manual I located.

 

[JVC Floyd]

can't remember if these have a battery backup or not but what I would suggest is to put a battery in the battery box to see if it's still holds the memory.

 

[jratz2k]

Thanks for the super fast reply. I can sure try that. The only batteries it takes are probably 8 D-Cells as I recall. I was sure hoping the schematic would reveal a button cell hiding inside somewhere but no luck.

As I recall, I almost never used it with batteries, always plugged in as it sat on my desk in college and workshop now but it is a great suggestion and a good work around if it works.. and pretty cheap to attempt.

 

[caution]

It may not be broken at all. Look at the manual screenshot below. It says that presets only last 48 hours without any source of power, and even then, you have to let the radio stay powered on for at least 30 minutes after defining presets before they will survive without power. This may be required to let the super cap reach full charge. Give it another try and wait 30 minutes before unplugging it (or removing batteries) to test preset retention.

If that doesn't work, then it's probably the super cap. Check C42 on the tuner board. It's an extremely high value - 47,000 microfarads. This acts as a type of short-term battery at this level.

I looked up the JVC part number for it and found that the V77 and X1000 also use it. However, only the V77 schematic correctly shows "0.047F" by the part - the V66 and X1000 schematics simply show 0.047 like all the other caps, which would lead one to think it's only 0.047µF (MICRO farads) which it most certainly isn't. The parts lists label it correctly as a super cap. You'll have to look at the part itself to determine its working voltage before you can select a replacement.

I'd be curious to know what "LS1" looks like - it's on all three models too, and sits in between the super cap and the tuner IC's power pin, on the LCD board. Curiously, JVC decided to leave it off the parts list, so there's no description for it. They just put its part number right on the schematic next to the part. LS reference designators usually refer to a loudspeaker or buzzer, but that doesn't make any sense in that spot. JVC possibly repurposed LS to refer to "special" inductors, because the symbol is a choke with a core. It may be a type of line filter. There's an identical second one on the LCD board, LS2, hanging off a pin adjacent to the one for LS1.

 

[jratz2k]

Thanks very much for your help. I should have read that. I'll plug it back in and let it soak for a retest. I'm the original owner of this unit and had it on my bench for years. The presets used to hold and eventually started behaving as they do today where they will evaporate immediately when just cycling the main power button.....even when the unit is plugged in the entire time.

I see that C42 enumerated in the Tuner Board (VMW2278) in this european diagram. Still looking for a USA version. I have seen the Digital boards salvaged from time to time.

Check out the attached... looks like the Tuner board and the DTS Board are two different things. I attached a picture of a DTS Board so you can see what looks to be in that LS1 and LS2 spot? if I'm getting my landmarks correct. Could they be the two white components identically labeled as 471J or something like that?

Thanks again! Amazing accumulated knowledge you have.

 

[caution]

Yep just a weird inductor, hah. Thanks for pics. 471J means 47 microhenries (µH) +/- 5%. (471 = 47 x ten to the "1ˢᵗ" power)

C42 won't vary across region, that only applies to differences related to tuning range and inputs for audio & power. I'd be curious to see a pic or know what's written on yours. Once you have the deets, go off to DigiKey or Mouser or something and snag a new one.