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My early 70s JVC lust has been my undoing... Need help :(

R

ReVoxFan

New Member
I picked up a pristine JVC 4VR-5414 Quadraphonic Receiver; I've got a weird thing for these older dark-faced beauties:

IMG_8095.jpeg

Unlike many of the other models, there are a couple of very early "ICs" in this one. Namely, it contains a few examples of the Hitachi FA6001 and Hitachi FA6012. Documentation shows a couple of simple diagrams for these, minus any values of course:

ICs.png

The Hitachi FA6001 is used in IC501 and IC502 and the Hitachi FA6012 is used in IC601 and IC602

The problem: Both FA6001 and FA6012 contain 2SC458 transistors

Does anyone have any experience fabricating teeny replacement boards for these? Any plans for replacements lurking in some dark corner of someone's hard drive, perhaps?

Many thanks in advance to anyone who can throw me a life-jacket on this one!
 
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If that really is the circuit, you should be able to (mostly) work out the resistor values with a meter. You could then sub KSC1815 (or KSC1845) for 2SC458.
 
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redk9258 said:
Of that really is the circuit, you should be able to (mostly) work out the resistor values with a meter. You could then sub KSC1815 (or KSC1845) for 2SC458.
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Cheers. Yes, I regularly use the KSC1845 to replace 2SC458s. TBC I have merely read that these ICs contain the 2SC458. It would be excellent to learn that I am simply wrong on this fact! ;)
 
Ah, well that would be splendid news indeed! I'm not looking to have any unnecessary adventures in perfboard, personally... There are 16 other 2SC458s in this receiver, so not having to struggle with them in weird IC form is a blessing :)
 
Why are you concerned about the 458 in an IC? There is only the one 458 that is on the replace on sight list and it is not one built into a chip.

Are you having problems with the 458s in your receiver? Pics will allow confirmation of the replacement need of them. That unit might well have the bad actor transistors.
 
Blue Shadow said:
Why are you concerned about the 458 in an IC? There is only the one 458 that is on the replace on sight list and it is not one built into a chip.

Are you having problems with the 458s in your receiver? Pics will allow confirmation of the replacement need of them. That unit might well have the bad actor transistors.
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They're not *actual* ICs in the modern sense. The Hitachi FA6001 and FA6012, both present in this receiver, were simply a pair of transistors and a handful of resistors on a small board wrapped in dielectric insulation with eight pins coming out of them, so again, not a real IC in the modern sense, but no need to split hairs there. The reason why I'm seeking options to replace them is that a pair of them sit in the very beginning of the phono-stage in this receiver, and the stage is embarrassingly noisy. This noise is not detected anywhere outside of the phono-stage, so obvs these become highly suspect.
 
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ReVoxFan said:
They're not *actual* ICs in the modern sense. The Hitachi FA6001 and FA6012, both present in this receiver, were simply a pair of transistors and a handful of resistors on a small board wrapped in dielectric insulation with eight pins coming out of them, so again, not a real IC in the modern sense, but no need to split hairs there. The reason why I'm seeking options to replace them is that a pair of them sit in the very beginning of the phono-stage in this receiver, and the stage is embarrassingly noisy. This noise is not detected anywhere outside of the phono-stage, so obvs these become highly suspect.
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Annotation 2026-08-05 165411.jpg

i saw them a while back in something i was going to buy and it changed my mind. as far as i have ever seen, there is no drop in replacement. i looked around and don't see where anyone has built a discrete replacement.

it's such a small marketshare, it would be a labor of love if someone ever made a sub for it. good luck.
 
painttoad said:
i looked around and don't see where anyone has built a discrete replacement.
Click to expand...
As mentioned above...
Bert Beukema

Thread 'JVC VR-5525 (LX) schematics'

Hi guys,

I'm working on a nice JVC VR-5525 receiver. It had several issues but they were all resolved. One issue remains: crackling on the right channel. I believe I have traced this problem to a single 33uF cap in the pre-amp. It is difficult to trace further because of the way it is constructed.

Problem is: to get at the PCB requires a serious amount of deconstruction of the machine. It is nearly impossible to reach it and it is fixed with at least 30 wires. Also the tuner thread is running through the pcb area and the case. To get it out will take me at least two hours of fumbling...
 
redk9258 said:
As mentioned above...
Bert Beukema

Thread 'JVC VR-5525 (LX) schematics'

Hi guys,

I'm working on a nice JVC VR-5525 receiver. It had several issues but they were all resolved. One issue remains: crackling on the right channel. I believe I have traced this problem to a single 33uF cap in the pre-amp. It is difficult to trace further because of the way it is constructed.

Problem is: to get at the PCB requires a serious amount of deconstruction of the machine. It is nearly impossible to reach it and it is fixed with at least 30 wires. Also the tuner thread is running through the pcb area and the case. To get it out will take me at least two hours of fumbling...
Click to expand...
nice. i did not read far enough in the thread. i had googled the fa6001 because that is what is in the phono stage. the fa6012 is in the flat amp.

redk9258 said:
If this is in the PHONO section, could you compare it to a newer model that maybe uses an opamp or discrete transistors to fab something on perfboard to replace the "ICs"?
Click to expand...

that'd be a cool project to be able to use smd parts and design a little breakout board. those 6001/6012 are not very big. if it's in a tight place it may be difficult to pull off with thru hole components.
 
Indeed, it would be a super cool project!

I've got the schematics for both the FA6001 and the FA6012 posted above, but resistor values are missing on both of them. However in the other thread there are resistor values listed for the FA6012 at least, so it seems that someone could rebuild the FA6012 right now with the info in both threads. I am seriously considering taking a stab at it, but I also need to rebuild the FA6001 as well, and I can't find any resistor values for that one listed anywhere... :(
 
redk9258 said:
If this is in the PHONO section, could you compare it to a newer model that maybe uses an opamp or discrete transistors to fab something on perfboard to replace the "ICs"?
Click to expand...
It's not a bad idea. Since the ones in this receiver are already so problematic, I'd almost like to remove the coating (epoxy?) from them and pull them apart, document what is really inside of these guys and then rebuild them on a teeny board... But that coating... not sure how best to tackle that. Acetone soak maybe.
 
Well fwiw, looks like this little JVC is a lost cause on multiple counts now. A shame, she sure is pretty.

I may have a poke at it down the road ... but one of the sdt-20 thermistors on an output transistor pair is no bueno. At room temp and zero power it reads 215-220 Ohms, but that should be more in the 275-300 Ohms range like the other three sdt-20 thermistors are. As the outputs heat up and the thermistors decrease resistance, with this starting too low to begin with, you will eventually get 3+ volts DC offset on that channel and the protect relay trips. SDT-20 thermies are unicorns, only to be found in spare parts units... I might get bored this winter and use a laser temp thermometer and a heat gun to establish the beta of these working sdt-20 thermistors and then try to use a modern replacement... Something like this with another slightly larger fixed value resistor in parallel.
 
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ReVoxFan said:
one of the sdt-20 thermistors on an output transistor pair is no bueno.
Click to expand...
I had the thermistor pop (explode) when I tried soldering a broken lead on this outside temp sensor wire. The internal temp still worked called Amtherm and they talked me through determining beta and other parameters. Then sent me a few in the mail. Thermometer works fine now and I learned about spec’ing a thermistor.
 
ReVoxFan said:
¡Sin duda, sería un proyecto genial!

He publicado los esquemas tanto del FA6001 como del FA6012 arriba, pero faltan los valores de las resistencias en ambos. Sin embargo, en el otro hilo sí aparecen los valores de las resistencias del FA6012, así que parece que alguien podría reconstruirlo ahora mismo con la información de ambos hilos. Estoy pensando seriamente en intentarlo, pero también necesito reconstruir el FA6001, y no encuentro los valores de las resistencias para este último en ningún sitio. :(
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Hola, hace poco hemos terminado de construir los FA6001 para un amplificador Sharp que lleva dos de estos módulos discretos. Dejo aquí el diagrama. Use transistores KSC1845FTA, En R2 puse una resistencia de 2.2k, antes de llegar a esa decisión puse un trimpot para ir regulando hasta encontrar el punto. Cualquier duda, aquí estaré.
 

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