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Attempting to repair a JVC 4VR 5456X CD-4 Demodulator Problems.

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Xdevo1973

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May 21, 2006
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Hi Everyone,
I wonder if any of you can help. I bought a JVC 4VR 5456X receiver and it sounds pretty good. I had a replace a preamp transistor in the right front channel which got it up and running quite well. I played some CD-4 records after I calibrated the separation and carrier and was more impressed as it sounds better than my Marantz demodulator; I was feeling pretty good until I hit this snag-the phono section does not want to play stereo records in both channels. If there's no CD-4 carrier, the left channel becomes almost silent. I've narrowed it down to the CD-4 board as I switched the left and right inputs to it-the inputs are working but one side of the board has either a dead capacitor or transistor. I spent hours trying to troubleshoot but to no avail. Voltage readings on the transistors mirror each other from the good side to the bad side. The capacitors seem to read right on my multimeter. Does anyone have any suggestions? Why would it pass all four channels with the carrier but only pass the right channel with stereo and matrix records?
 

Xdevo1973

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Hi Duncan, thanks to the link to the schematic-it helped. I had others from HiFi engine but not that one. I was able to identify a bad transistor (2SC458) on the left signal path of the demodulator board. I ordered a bunch of them and replaced it. This is the 3rd one I've changed in this receiver. JVC used this transistor in quite a few sections of this receiver and apparently they have failed after 40 plus years. Now everything sounds really good. Here's an interesting variable, though. I have a small fluorescent hockey puck style lamp mounted on the wall near to the receiver. Whenever the lamp is on, the CD-4 beacon illuminates; obviously this lamp is generating noise in the 30khz range which is being picked up by the phono cable. This is not a big deal; I just leave that lamp turned off.
 

DuncanS

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Hi Duncan, thanks to the link to the schematic-it helped. I had others from HiFi engine but not that one. I was able to identify a bad transistor (2SC458) on the left signal path of the demodulator board. I ordered a bunch of them and replaced it. This is the 3rd one I've changed in this receiver. JVC used this transistor in quite a few sections of this receiver and apparently they have failed after 40 plus years. Now everything sounds really good. Here's an ioventeresting variable, though. I have a small fluorescent hockey puck style lamp mounted on the wall near to the receiver. Whenever the lamp is on, the CD-4 beacon illuminates; obviously this lamp is generating noise in the 30khz range which is being picked up by the phono cable. This is not a big deal; I just leave that lamp turned off.
I designed some low noise 100Hz-100kHz instrumentation and couldn't figure out why I had so much HF noise, then I turned off the fluorescent light above the bench and it disappeared! So I discovered that Fluorescent lights generate quite a bit of E field interference.
 
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macdude

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Maybe this will help you, maybe it won't. I recently acquired a 5406 and had it apart, but haven't gone over it extensively yet. I noticed my fluorescent bench light also illuminated the Radar lamp. From what I've worked on in the past and the number I've changed that have gotten noisy with age, I would change all the 2SC458's in the demodulator. I'm not into shot gunning parts usually, but those transistors are KNOWN to become noisy. I use KSC1845 from Fairchild as a replacement. 2SC2240 was the better option, but they've been discontinued. Many Akai tape decks used the 458's too, as does the JVC 4-DD5 demod. A great, low noise transistor in it's day, but it didn't hold up.

I recently repaired the demod on my QRX-7001. A bad tantalum capacitor was attenuating the carrier signal in the detection area of the circuit. Took me a few attempts to find it and in the end it was an educated guess.
 

Xdevo1973

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I did indeed end up changing many of those 2SC458s; not only in the demodulator but also in the preamp and the auto CD-4/Matrix switching boards. The demodulator also needed an IC replaced. Now everything sounds really good. I'm actually playing the original CD-4 demonstration album that came with the receiver-4 the first time. It was a sealed copy. Interestingly, the first track has the same narrator who does all of the CD-4 calibration records.
 

Xdevo1973

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The ICs are CD894. I now have an extra one just in case. I have a new question though. The 5456X seems to have two different rating plates on the back. I’ve seen pictures online with the power usage at 320 watts, but mine reads 190 watts. What is going on here?
 

Circular Vibes

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Are you sure the different plates are from the X model? I have read elsewhere that one is a Canadian model, the other is US. I do not remember which is which. I would go by the specs in the service manual. I would assume that there may have been "improvements" to later receivers. It could also be from different ratings standards in various countries. As to replacing the 2SC458 transistors, nexxt time my 5456 goes in the shop, I will be asking about replacing them. Mine has been in twice for dead channels(not the same one), the second time it took out the power supply capacitors as well. Even with the repairs it is still my favourite quad receiver. I have a QRX7001 and a Sylvania RQ3748 as well.
 

Xdevo1973

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Yep, the different rating plates are on the same exact x model. I really have no clue why they did that. I have now seen 3 different plates, the lowest saying 190, the 320 and another one stating over 500 watts! They can be seen in google images. I don’t think that even an ammeter or kilowatt device would help that much, since I’d have to drive the unit at full power to see. I really don’t want to do that.
 

Xdevo1973

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Are you sure the different plates are from the X model? I have read elsewhere that one is a Canadian model, the other is US. I do not remember which is which. I would go by the specs in the service manual. I would assume that there may have been "improvements" to later receivers. It could also be from different ratings standards in various countries. As to replacing the 2SC458 transistors, nexxt time my 5456 goes in the shop, I will be asking about replacing them. Mine has been in twice for dead channels(not the same one), the second time it took out the power supply capacitors as well. Even with the repairs it is still my favourite quad receiver. I have a QRX7001 and a Sylvania RQ3748 as well.
I’ve found the 2SC458 transistors made by Hitachi to have a high failure rate. They failed in low power sections such as the preamp, demodulator and auto CD-4/matrix switching board. I was able to purchase 50 for about $5. Not hard to change at all.
 

Circular Vibes

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Looking at the pictures on Google, I see 3 different back plate versions. The US model appears to state 420 VA. Besides that anomaly, I think the answer is the model in Canada has lower watt ratings due to a smaller transformer for only 120 volts. The version for universal use is 520 watts, probably due to the larger primary windings for 220/240 volts. I am not at home to look at mine, but I seem to think it has only 120 volt capability. I will report back later this week after I see mine.
 

Xdevo1973

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Mine has a voltage selector on the back and is rated for 100-240 volts. It calls for a 5 amp fuse when running at 100-120 volts, yet states 190 watts. So odd.
 

Xdevo1973

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I’m not sure if this will work. Here’s a link to the picture since the upload is too large.
 

Xdevo1973

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Mine actually does have 4 settings, even though the plate lists only two voltages. The settings are 100, 120, 220 and 240 volts.
 
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It's been nice to follow this discussion of the JVC 5456. I've had mine for a year now, and use it every day. Recently I picked up the joystick for it, and find that makes the quad experience even nicer. I think the "x" model doesn't have the stereo separation knob, but I'm not sure if there are other differences.
 

Xdevo1973

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May 21, 2006
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Indeed, the X model doesn’t have the separation control. The only other difference I know of is the decal on the Tape 1 switch. The X model reads NR/Tape 1, suggesting in the instructions that this tape loop would be the one used for an outboard noise reduction unit. I use the Tape 1 loop for my Involve Surround Master.
 
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