Sansui QR 4500

[sKiZo]

?

Pretty much finished it in the thread, or so I thought. Mostly just buttoning it up and adjusting when I left off.

Worked out fine when done, with major improvements in the bottom end and clarity. Can't complain, but ... wasn't long after, I stumbled across ... my precioussssssss ...

Sorry to say, the QR4500 has been collecting dust since. No knock on it ... but the QRX 9001 has much more ... muchness ... (sigh).

PS ... that was also a project and a half, as it (and me) suffered a full restoration to bring it back to it's original glory.

But ... that's another thread.

Have fun with it!

 

[Bert Beukema]

LOL. I'm in Europe, finding a Sansui QR 4500 in good condition is already a godsend. The 9001 is a fantastic machine but falls squarely in the 'unobtainable' category over here.
But man.... those meters ... just .. wow. In any case, mine is now restored and looks & sounds like a factory new baby. Really happy with it. But man. Those 9001 meters........

 

[patra710]

I pick up a QR-4500 that just barely worked. I rebuilt the tone board and running a signal through the 4 channel inputs I get a clean signal at the pre outs. The 4 channel inputs runs right to the tone board. Tone board is working good.
When putting a signal to the 2 channel input, the front is good at the pre outs but the rear is weak and about 108 degrees out of phase. I have no idea what the synthesizer and phase modulator boards are doing. There are a lot of ICs on them that I can find no information on. Also some pots that I don't know how to adjust. And the service manual lacks any help.
Very few voltage references. And I can't believe the ones that are given, example, it show a 25 volt at on spot on the synthesizer board but it is running off a 25V E-cap. I am getting about 17.9V at that spot which I believe is right because they wouldn't run a cap right at its rating.
There isn't much information on this receiver on the internet. Can anyone point me in some direction to find something on this stereo?
Thanks

 

[sKiZo]

Not all that sure what you're talking about by "out of phase" ... that's what quad synth does?

And ya, it's been a while since I did mine, but it wasn't all that uncommon to push caps right up to (and sometimes beyond) ratings. It was always fun trying to cram those big old school caps in. Also common in my experience to have the synth section running off a 25v supply ... both the QRX's I worked on were also in that range as well. One thing worth mentioning ... those VRs are EXTREMELY sensitive, and you need to be careful not to fry those unobtanium ICs.

You say you've got the service manual? Page 14 has the basic current adjustment procedures, and you'll find a list of the corresponding test points on page 7. Do that if you haven't already done so, and proceed from there. The included schematic does have quite a few voltages listed, but you gotta have really really good eyes to spot them. If your voltage is actually low, I'd suspect the big ceramic resistors in the power block. Next step might be to check the complimentary transistors with the copper straps on the F-1180 as those tend to go south and throw things off.

But man.... those meters ... just .. wow. In any case, mine is now restored and looks & sounds like a factory new baby. Really happy with it. But man. Those 9001 meters........

Just to feed your fetish and keep you looking ... <G>

 

[Lavane]

Film caps to replace small value electrolytics?

Having problems finding replacement caps for some of the low voltage electrolytics on the synthesizer boards.

1.5µF @15v
3.3µF @25v

Can I replace these with film caps in the same values? Those are rated at 250vdc, but are NOT polarized. Size shouldn't be a problem. I know substituting bi-polar isn't wise, but ... not sure about this. Only other issue I've seen is maybe additional crosstalk in the circuit due to the fact that they're not shielded. Heck ... if that's a problem, a quick wrap with foil duct tape should take care of that.

There's also a boatload of 1µF and other such small values that might benefit from the additional stability a film cap could bring.

My usual go to to replace small value lytics are Wima stack films. If you cant find one that has the proper lead spacing, soldering them on the underside works. Nice work! Is that a nixi tube I see to the left!?

 

[sKiZo]

Proof positive old threads never die ... My rebuild was five years ago now. <G>

If you're talking about the 2/4 channel display on the front panel ... no, not a nixie (although that would have been kewl). It's a prism block with two wheat bulbs in it - one lights for two channel modes, and the other for four, and each lamp lights it's own layer. The back layer is lit by yet another bulb that gives the same background for both. Kinda neat really.

Sansui must have liked it ... they had the identical indicator in the QRX 6-7001's, just a different color.

PS ... they did have fun with light transmission in these old monsters. The 9001's entire front panel is lit by three bulbs on the left side of the faceplate, with a surprisingly even output all across the dial.

 

[patra710]

Not all that sure what you're talking about by "out of phase" ... that's what quad synth does?

Thanks I really don't know what to expect from these boards. I am testing at the pre outs leaving the amp boards out of it for now. When I hook my scope probes to the front pre outs, the signals will match up with each other when I adjust the move the signal up on the scope. On the rear pre outs, they don't match up. I did find this web page
http://www.4channelsound.com/sansui.htm
Also while probing the boards with my scope and when turning the synthesizer/ decoder knob the signal will double in size on the scope. So there are a lot of things that I need to learn about quads.
I will start by looking into the 25 volts. But this receiver has other problems. The 6 big caps will all charge up to 40 volts except one which only goes to 20 volts. And one of them doesn't discharge, it will hold its voltage for days, maybe longer.
And yes I always meter out a cap before I touch it.
I will keep on going with this receiver till I get it done. I did find some of the ICs on a site in the UK.

 

[Bert Beukema]

Make sure that you have the correct service manual (QR versus QRX version) it makes for quite a bit less headache. The old voltage measurements are often off when checked with modern equipment or when changes have been made to transistors / power rail / etc. The bigger question is if it is a consistent value over multiple channels. If it is then it is either 'normal' or something earlier in the chain is throwing the values off. I would immediately change the entire power rail if you haven't done this; especially if the main capacitors are playing up (there are a damn lot of them). When I did this I also rewired the entire thing because of the old wires breaking. Every board you change should also have the soldering paths checked, I would retrace / reflow them all.

 

[Bert Beukema]

Just to feed your fetish and keep you looking ... <G>

Damn. That is really nice looking, no question about it. Those machines can be found in the USA with relative ease but over here nada. And those who come on the market are priced in the 'no sir, don't like it at all' range. People selling these machines know their money printers. Still, perhaps someday i'll find one on the attic of some old French barn ;-)

 

[Natitude]

I'm picking up a QR-4500 this Thursday. This thread has been great... thanks! I did want to pass a long a link I just found. You can type in whatever receiver manual your needing and download it in PDF format for a small fee. Hope this helps!

https://themanualsservice.com/

 

[Bert Beukema]

You can also go to HiFi engine and download them there, free of charge. It's a community system, which means that if you have any schema's or manuals yourself it's appreciated if you scan and upload them for others ;-)

 

[wmm766]

Hello,
I recently purchased a QR-4500 and I love it. The controls were scratchy to the point of not working properly and it had a few lights out. I fixed those problems with some DeoxIT and new lights. My problem at the moment is that it is pretty much a TRI-phonic receiver... The back left channel (when connected) makes awful pops and white noise.
I traced it down to the F-1180 board. If I swap the boards, the issue moves to the front left channel.
I replaced all the electrolytic capacitors on the left channel of the afflicted board (and found / fixed a short across VR801), but it didn't fix the problem.
Any ideas where to go next?

Also, the signal meter and "Stereo" light are very weak, even with what sounds like a really good signal. That's a much lower priority, though.

Thanks.
Bill

 

[sKiZo]

On the 1180 board, I'd suspect the paired NPN/PNP transistors. Replacing those made for some substantial SQ improvement on mine. Most will have some serious corrosion on the cans from the copper straps, but it's more internal breakdown from heat that makes them go south. OEM transistors are hard to find, but NTE makes matched sets that plug right in. (NTE129MCP). Just polish the old straps and reuse those.

Don't know what to tell you about the meters. Maybe you just got to feed them more signal. Never had any luck with indoor antennas here, but going with an outdoor rig lets me fill the meters nicely.

 

[wmm766]

Thanks. I'll look up those transistors!

 

[sKiZo]

Just make sure you follow the pin markings as those can change with substitutes. Can't say as I remember whether that was an issue with these or not.

Be sure to report back with your results. Inquiring minds need to know.

 

[wmm766]

They were backordered for three weeks, but should come this week☺

 

[sKiZo]

Not a common part, so the delay is no surprise. Best o'luck ... just a guess on my part, but I figure the logical place to start. ;-}

 

[wmm766]

I replaced the transistors, but still no joy in the left channel. The right side is great. Just quiet with occasional heart stopping crackles on the left...

 

[wmm766]

So, I got a QRX-6500 on eBay (I'm trying not to make it a habit). It had a couple of issues that I fixed and the last thing to take care of was the tuning dial string... It was slipping and I could tell the part that goes around the flywheel was not as tight as it should be (it is a 2 string setup). Also, it was not strung according to the manual, so I decided to restring it. As I was working on the string, I was listening to the radio, because it was the only radio in the room and I was impressed with how it sounded. I thought to myself: "Self, you should really have the power disconnected while working on this." To which I replied: "Self, I'm just working on the string. It'll be fine." About 5 minutes later, I dropped my tweezers into the case and all the lights on the receiver went out...

I think I shorted the right-most dial backlight to the case. Everything else seems to work. Even the meters. Just no lights. Any advice for starting troubleshooting would be greatly appreciated.

 

[wmm766]

Upon reviewing the schematic, it looks like there is a fuse. Of course, they soldered it in and it is way up inside...