Sansui QRX7001 repair

[SPXER]

Which side of C52 are you looking at? Do all three components at that node (transistor, resistor, capacitor) read exactly the same?

All three nodes read the same 17.78v dc

If there’s an AC signal on the base of TR12,

1.5mv ac

you should have about the same signal in the emitter (with about a 0.6VDC lower reading), and a signifigantly larger copy of that signal (polarity reversed) on the collector, as well as on both sides of C52.

Only 3.5mv ac at C52 vs 39mv ac at C51 (same place in identical circuit)

It’s possible that the output side of C52 is loaded heavily. That isn’t shown on the schematic, but of course it goes somewhere, and that might be shorted.

I pulled the output wire on C52- no difference.

I have looked the circuit over multiple times and I can find no other visible issues. (broken traces, solder bridges )

I do not seem to have a signal at C40. I do have a signal at C24. Can I safely jump from C24 to C40 to see if the signal then goes through the Transistor TR12 to C52?

 

[SPXER]

What temperature are you using on your soldering iron? The more heat you use the higher risk of lifting tracks.

I have no idea of the temp. Owen. The wattage label is faded. It is not my hottest iron. That one burns the tip up. I used it on the tube rebuild.

 

[Owen Smith]

I have no idea of the temp. Owen. The wattage label is faded. It is not my hottest iron. That one burns the tip up. I used it on the tube rebuild.

So it's probably not temperature controlled. The temperature on those is usually reached when heat out matches heat in, and they can run rather hot because otherwise they take ages to heat up in the first place with a lower wattage. My Radio Shack 17W iron which is decades old gets very hot after a while, so hot I don't like using it any more.

When I started my tuner recap project one of the first things I bought was a temperature controlled iron for £48, it was a great purchase especially given the tuner was made with unleaded solder:

https://www.amazon.co.uk/gp/product/B08YDG9LYP
The solder sucker in the above kit is rubbish and I haven't used the lead free solder or many of the accessories that came with it. But the iron itself was a great purchase.

 

[barfle]

I do not seem to have a signal at C40. I do have a signal at C24. Can I safely jump from C24 to C40 to see if the signal then goes through the Transistor TR12 to C52?

It looks like VR16 and VR20 are tone controls, and that most of the signal comes from those two pots. It’s odd if they are both bad and the other channels’ pots are good, but we’re dealing with odd anyway, so I’d tru comparing signals on the wipers of those two controls first. It’s unlikely to cause any trouble connecting the right side of C24 to the right side of C40.

 

[SPXER]

Yep, I found another trace break. I am not happy with my work. Got to be more careful. The break was at C24. Difficult to see, but the meter told on it. Repaired that and the amp works on all 4 channels. I hope it doesn't look too bad. I want to heap praise on barfle for talking me through this bit. I am pleased that I am learning how to go through these circuits step by step. Now on to the 2428 board.

 

[SPXER]

Also found another misprint on the board. R40 is labeled as R42. That through me off for a while.

 

[barfle]

Yep, I found another trace break. I am not happy with my work. Got to be more careful. The break was at C24. Difficult to see, but the meter told on it. Repaired that and the amp works on all 4 channels. I hope it doesn't look too bad. I want to heap praise on barfle for talking me through this bit. I am pleased that I am learning how to go through these circuits step by step. Now on to the 2428 board.

You’re most welcome. I’m an old circuit designer, and it’s something I still enjoy on occasion.

I recall once when I was the project engineer on a single-board product, the circuit board came from the vendor with enough opens that we had to scrap it. I think I found five opens on that one board, and I decided I couldn’t send out such a piece of junk as a product under warranty.

 

[SPXER]

I put the QRX in the front room to hear it on speakers I am used to. 2 channel only so far. It sounds good, but different from my Kenwood KR-6030. It will take some getting used to. The Kenny is all original except for some LEDs.

 

[SPXER]

The tuner on the QRX is pretty lousy. Lots of noise like on a difficult to tune station. I looked over the FM alignment instructions, but I don't have the equipment to perform that.
I assume it can be made better? My Sansui 2000x is better and the Kenwood is very good.

 

[mandrix]

I can't help. But I would note all the Kenwood Quad AVR's I had, had excellent tuners.
I -think- I had 3 different ones. I believe, though can't verify, the last one I had was in the 9xxx series. It had the CD-4 modulator that slid in from the rear.
I had a big Sansui but sold/traded it off. Wish I had kept it, but shipping back to the States was a little pricey.

 

[par4ken]

The tuner on the QRX is pretty lousy. Lots of noise like on a difficult to tune station. I looked over the FM alignment instructions, but I don't have the equipment to perform that.
I assume it can be made better? My Sansui 2000x is better and the Kenwood is very good.

I wouldn't attempt repair without the proper equipment or you could make it worse. It might be an actual component failing and not just the alignment. I'm sure that it could be made better, but is it worth the bother?

If FM is important to you why not just use a stand alone tuner. Great vintage units are available for very little money.

 

[barfle]

The tuner on the QRX is pretty lousy. Lots of noise like on a difficult to tune station. I looked over the FM alignment instructions, but I don't have the equipment to perform that.
I assume it can be made better? My Sansui 2000x is better and the Kenwood is very good.

It’s always rewarding when you bring some old piece of equipment back from the dead. I remember getting an old Hoover vacuum cleaner working better than factory new. We used it for years, but had to give it away when we used it to clean up a house we sold after the movers had gone, and we couldn’t fit it in the car, literally.

RF alignment isn’t rocket science, but it is science, and the right test equipment is pretty important. If you want to use it as a learning experience, and it’s OK with you that it ends up broken, I’d say give it a shot, but it’s your stuff and your call.

 

[SPXER]

I wouldn't attempt repair without the proper equipment or you could make it worse. It might be an actual component failing and not just the alignment. I'm sure that it could be made better, but is it worth the bother?

If FM is important to you why not just use a stand alone tuner. Great vintage units are available for very little money.

Yes, the local public radio stations have some very good broadcasts. Jazz, alt rock, blues, and pipe organ programs. Any recommendations on specific tuners?
My Kenwood has tape record outputs. I've never used a tape machine. Would radio reception be available on those RCA sockets?

 

[mandrix]

Yes, the local public radio stations have some very good broadcasts. Jazz, alt rock, blues, and pipe organ programs. Any recommendations on specific tuners?
My Kenwood has tape record outputs. I've never used a tape machine. Would radio reception be available on those RCA sockets?

If you mean it has inputs, then yes you can probably plug a tuner in there.

 

[par4ken]

Yes, the local public radio stations have some very good broadcasts. Jazz, alt rock, blues, and pipe organ programs. Any recommendations on specific tuners?
My Kenwood has tape record outputs. I've never used a tape machine. Would radio reception be available on those RCA sockets?

Yes, you could use the Kenwood tuner connected from its tape output to the Sansui's input.

 

[SPXER]

Thanks, parken

 

[Doug G.]

Lousy FM can be caused by a dirty tuning assembly, both dirt between the tuning plates and in the bearings/contacts. Symptoms are difficulty in getting it to remain on a station, weird noises, and it being way too sensitive to movement.

Doug

 

[SPXER]

Even after hooking up the Kenwood tuner to the QRX there is noise. It seems that the noise is steered (in surround) to the back (side in my case) speakers and amplified. I have not yet changed anything on the surround boards.

 

[par4ken]

Stereo FM is inherently more noisy than mono, often noticeable on week stations. Adding a good antenna often helps. The extra noise would be present on the stereo deference signal which is mixed out of phase between left and right and so would show up in the back channels due to that phase relationship.

My Nikko Gamma FM tuner has a blend button to reduce the noise on week FM stations, it sacrifices a little bit of separation in the process.

Unless the noise is also there on cleaner sound sources I wouldn't suspect the surround boards at all. Not a bad idea to do some re-capping though.

 

[SPXER]

I have an outside FM antenna. An old Radio Shack thing. Strangely, when I put it up, I could not get a good signal from my preferred station. I rotated it in all directions and set it at different locations. Nothing gave a good signal. I leaned it against the house and went inside in frustration. Glancing at the signal meter again, I saw it was over 5! Setting vertically on the ground against the house. So, I mounted it vertically on the tower and it does great that way. The moral of the story is, disregard the instructions.

I do have the caps for the surround boards. I just need to find the time to finish.