ELzekio

Active Member
Hello Everyone.

I recently obtained a JVC RX-999V Reciever (this reciever is one steo down from the top of the line reciever jvc made in the 1980s, the JVC RX-1001V).

The Seller claimed that it did not power on. When it arriaved i i pluged it in and turned it on and quickly realised that the unit did power up but it has a few issues.

The first issue is the im hearing only one relay click. Looking inside the unit i see two relays, one for when the unit powers up and one in thr amp section to activate the sound. The power relay is the only ine clicking ofcource.

The other issue is that the display is not lighting up.

Im looking into the display issue first before i try looking into the amp section. First thing i did was open the unit up and take a look at the bulbs and lone behold all 4 of the fuse lamo bulbs are burnt out. They are all the origional 8v .2 amp fuse lamps. Lucky for me i have enough fuse lamps to replace all of them but before i do so i see something that i would like some of your guys opinions on.

One the board that has the clips for the fuse lamps ther are three zenner diodes as pictured below, but as you can see the board is totially cooked. Dont think ive seen a more cooked part of a board.


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I took these diodes and tested them and it looks like two of them are fried. What i was thinking of doing is replacing these diodes with the functioning diodes on a very similar board for my JVC RX 9v part unit as pictured below

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My only concern in doing so is im not sure if these diodes are the same spec and/or if they are interchangable because if you look at the Parts list for the JVC RX 999V they label the diodes used in there reciever as Part Number: "MTZ8.2JC"

While the part number in the jvc rx 9v for the diodes is Part Number: "MTZ12C"

Both are zenner diodes by ROHM

Both sets of diodes preform a very similar function but i just want to make sure i do things right before i move on to the other issues of the amp.
 
MTZ8.2JC are 8.2 volt zener diodes. MTZ12C are 12V zener diodes. 1N5237B is a good sub for the 8.2V part. 1N5242B is a good sub for the 12V part. I would not scavenge parts to swap out as they are very cheap to buy. Do you have a diagram for it? If it is like my RX-950V, there are a couple of resistors up the line that probably burned up if any of these zeners have shorted.

Look at this post for more info... http://audiokarma.org/forums/index....display-lights-burnt-out.583171/#post-7678707
IDK if the RX-999V is the same circuit or not. It looks like those zeners are cooked though.

It's odd that the RX9V has 12V zener diodes and I assume fuse lamps and a year later they used 8V bulbs with 8.2V zener diodes on the RX-950V.

BTW, I believe the diodes are there to make the bulbs the same brightness in case they are slightly different. It's kind of a crappy design. Should have just added a tap on the transformer and ran them in parallel.
 
Hey, I just realized that I have the service manual for this receiver. I bought it with a few others in a package. This receiver has 4 fuse lamps, right?
 
Yes, i actually bought the servise manual to, when i bought the reciever. Does yours have all the extra service bulletins and suppluments? I can scan them if you dont.

Yes it has 4 bulbs, not 3 like the 9v or 950v recievers. I believe the i believe the origional bulbs for the 999v were 8v .2a (not .25a).

Not exactly sure if all of RX receivers originally had 8v .2a bulbs, as i have not seen them in my 8v or working 9v/950v but all of those could have been replaced before hand.

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You posted that as I was asking what it was. Please scan this in and add it to the database here and maybe on this post too. I wish I would have know about this in the past. I bought a RX-750V from a recycler that had this problem. It burned up those resistors on the amp board so bad, it has a hole in it. I know what I am going to be ordering soon and changing my receivers to.
 
Not exactly sure if all of RX receivers originally had 8v .2a bulbs, as i have not seen them in my 8v or working 9v/950v but all of those could have been replaced before hand.
I know that the RX-750V and RX-950V came with 8V 200mA fuse lamps. Apparently the RX-9V used 12V lamps. The SM I downloaded is missing the page with the part number, so I can't be 100% sure. The zener diodes and resistors are different values.
 
Ill be getting a paypal card tomorrow so i suppose i could add an extra 7.50 and see what the issue is. I hope to have some time during the weekend do then do some more looking.
 
looks like you are right. this here is the corrected statement.

Service bulletin for JVC RX-999VBK.gif

I will get a pdf of the two set and a third service bulletin for everyone to see when i can later.

If you search for the new recommended duode "RD8.2FB3" on google you will see that it is equivalent to the NTE5072A zenner diode. If you do an ebay search for "NTE5072A" you should see multiple sellers selling them. I ordered some.

Do you think it would be best to use 8v 200 ma bulbs for the display, or does it matter if you use 12 volt 150 ma? Ive got some of both coming in the mail.
 
Thanks for posting that. I ordered bulbs from JVC once for my RX-750V and they subbed 12V 150mA. The originals were 8V 200mA. The brightness was fine. I think either is fine as long as they are all the same.

There are real diodes available from Digikey or Mouser. Search 8.2V 1000mA DO-35.
 
Thanks for posting that. I ordered bulbs from JVC once for my RX-750V and they subbed 12V 150mA. The originals were 8V 200mA. The brightness was fine. I think either is fine as long as they are all the same.

There are real diodes available from Digikey or Mouser. Search 8.2V 1000mA DO-35.

Yea i know you have to be carful of all the fakes on ebay. I always make sure im buying from a good USA seller. Mouser is nice when you are buying multiple items, but it stinks when you only need a couple cheap things because you get an 8 to 9 dollar shipping charge.
 
Well an intresting development to say the least... I remember taking a quick look at the voltages that are supposed to power the fuse lamps and it seemed one voltage may be off. Looking at the schlematic i seen the lamps were powered by the area in the red box. When i took a look at the board it was clear something was wrong.

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I have a section of resistors that have absolutly cooked the circut board, you can even see a bit of a crack in the board from the heat.

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That's because one of the diodes shorted and cooked the resistors. Hopefully you can patch it up and get it going again. Those should be flameproof resistors. That board looks btter than that RX-750V that I bought at a recycler. It had a hole burned in the PCB about the size of a nickel. You can patch that one up with some epoxy or something on the top.
 
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I'd start by checking the DC offset. You can check it at the emitter resistors. DMM negative lead to ground and positive lead to the end of the resistor with one pin.
thisone.PNG
 
I took those risistors out to test them and it looks like some of them are shot. Not getting anything when i test the ohms for these are the ones im looking at

image.jpeg And

Would i be fine if i search something like a 56 ohm resistor and 1/4th watt or should i look for something specific reguarding the UNF.CARBON or O.M.Film description?

I see a couple catagories of carbon resistors.
http://www.mouser.com/Passive-Components/Resistors/Through-Hole-Resistors/_/N-7h7z5/
 
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