Toshiba SA-304 Quad Receiver has arrived, but with DC Offset problem?

ToTo Man

ToTo Man

NEVER ENOUGH TOTO!
My latest acquisition arrived yesterday, a Toshiba SA-304 Quadraphonic Receiver. The cost? Wait for it........ a whopping $8.75USD! :banana: :D
Got it from the same seller I got the Sony STR-6800SD from, so another gamble, as he didn't know whether it worked or not. I was pleasantly surprised at how well wrapped this little guy was, especially considering the seller was only making $8.75 out of the sale. It was literally QUADRUPLE BOXED! Probably the sellers response to my polite request to make sure it was packaged adequately :D.

Got quite a shock when I opened it. There was crud, dirt and what seemed like rust all over the unit. As you can see from the following photo it wasn't a pretty sight :nono:.
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So, before doing anything else, I decided to give it a thorough cleaning. It literally took my half of yesterday just to clean the damn thing! Fortunately, every knob on the face plate could be easily pulled off, which made cleaning much easier. To clean the faceplate and knobs, I used an old toothbrush dipped in soapy water, and it worked surprisingly well. Even the stuff on the faceplate that looked like rust came off. So, I dried it off, but I could see opaque smearing in some parts. So, I sprayed the toothbrush with DeOxit and gave the faceplate another rub down and voila, I got a beautiful consistent shiny finish. I wiped down the wood casing with some damp kitchen towel, and I attacked the rust on the vent grill with a tooshbrush and soapy water. Unfortunately, the grille still has visible rust, but everything else looks brand new! :banana:. I love the knobs on the faceplate. Everything is heavy and well built. Here's a nudie for y'all! :thmbsp:
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I scrubbed the outside of all the RCA jacks with a toothbrush and Deoxit, and I also squirted some inside the jacks just to make sure. The receiver is now in a clean condition to test out.
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So, after replacing the power socket I turned it on. The tuner station bar lights up, but the blue signal strength meter bulb is out :sigh: . I don't hear a relay clicking in, but then again, this unit might not have a relay. So, I switched it back off, hooked up the multimeter to the speaker terminals, and switched it back on. 2 seconds after switching on I get an initial reading of 160mv, then after 1/2 second this fluctuates erratically, changing many times a second, fluctuating between -160mv and +160mv. So, I leave it for a few minutes and come back. Now, for the majority of the time it's between -15mv and +15mv, but now and then for a split second it will shoot back up to >100mv, then come back down again. There is no pattern to these fluctuations. Should I be worried? I'm hesitant to hook up a good set of speakers with erratic readings like this. Should I play safe and only use 'sacrificial speakers' on this unit?

BTW - This is my first introduction to quad so I don't know what half the settings are for. Guess I'll just need to try them and see what they do and hope I don't let the 'magic smoke' out! :D
 

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I dont think you'll have a problem with blowing speakers, just keep the volume knob turned down upon initial testing.
Try using cheapo speakers just for an hour of initial testing, and if they are fine, throw some good speakers on it.
Try running music with the multimeter as well.
 
Well, I hooked up a pair of speakers, and the good news is that the receiver works (though so far I've only tested FM), but the bad news is that there is a constant low-level noise coming from the right channel (a bit like pink noise). The noise is constant, and is independent of the volume control and independent of the source selected. Any ideas what this could be?
 
Sounds like leaky caps to me. If you are so inclined, grab a service manual. Its most likely leaky caps on either the driver or pre-amp/tone board -- or possibly both.

I don't suppose this has pre-out main in jumpers? if so, dpull the jumpers. This will let you know if the pre-amp or amp section is at fault. If the noise remains while the jumpers are pulled, the problem is on the driver board.
 
The Toshiba looks great. You did a good job of cleaning that unit up. Good pictures also.

jpdylon may be right about a capacitor causing the noise, although, it could be a resistor or transistor. If it is a leaky capacitor, it may reform itself if voltage is applied over time. I would leave the unit on for a day to see if noise diminishes.
 
Thanks tcdriver. Took me a while with the cleaning but I got there in the end!

I was going to ask whether it was safe to play it if it has a leaky cap?

I've hooked up a CDP and so far I'm not overly impressed with the sound quality, but then again I am comparing it to things like the Sony STR-6800SD and Yamaha CR-820 which it probably isn't in their league anyway. Other than added background noise, will the sound quality be impaired by a leaky cap?

BTW - How did you find out the specs on such a rare unit??!!!
 
If it has not been played for a while, all the capacitors could be compromised. Leaving the unit on for a day will allow the capacitors to reform to some extent. Once reformed, the unit will sound better. If the capacitors are too far gone, the only fix would be to replace them. That is a big job on a quadraphonic receiver. i.e. there are a lot of capacitors to replace. Also note that the receiver does not have a lot of power and can more easily be driven to distortion than the more powerful receivers you have. However, it will play quadraphonic records. :thmbsp:
 
A couple more symptoms which might give a better idea of what's wrong:

- There is a smell coming from a certain area of the receiver (see red circle in photo), a smell which I don't think I've smelt before on my other amps/receiver.

- When I switch the receiver off while the CD is still playing, the sound continues for three seconds after switching off and then fades away to nothing.

Do these symptoms point towards leaky caps?

If it turns out that I need to replace the caps, I think I'll politely pass, as I've never recapped anything before so it would probably be too big a job for me! :yikes:
 

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ToTo Man said:
When I switch the receiver off while the CD is still playing, the sound continues for three seconds after switching off and then fades away to nothing.

Do these symptoms point towards leaky caps?

If it turns out that I need to replace the caps, I think I'll politely pass, as I've never recapped anything before so it would probably be too big a job for me! :yikes:
Click to expand...
The unit playing after it is turned off indicates that the power supply capacitors still have reserves that are slowly drained away. If anything this would suggest that the power supply capacitors are OK.

I hear you on the job of replacing capacitors. It is not something that I would look forward to doing. However, like I wrote before, leaving the receiver on for a good period of time may allow the capacitors to come back to life. It is worth a try and costs almost nothing. Good luck.

ToTo Man said:
How did you find out the specs on such a rare unit??!!!
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Some information can be found in the following thread:

http://audiokarma.org/forums/showthread.php?t=73939
 
THe smell could just be warm dust. The heatsinks aren't getting hot are they?

The continous sound even after shutting iff the receiver is typical for a capacitor-coupled output stage -- which this receiver more than likely has. It doesn't indicate leaky caps.

Re-capping isn't difficult if you know how to use a soldering iron. Besides, if you're going to pass anyways, I'd give it a shot. That way you can't cry over it if its not something you cherish.

EDIT: **Man, TCDriver beat me to it** :D
 
jpdylon said:
THe smell could just be warm dust. The heatsinks aren't getting hot are they?
Click to expand...

The vent grille is barely luke warm, so I don't think the heatsinks are too hot.
I don't know when this unit was last used but judging by the state it was in when it arrived I'd say it's been in someones attic for the past 20years! Perhaps you're right and it's just burning the 'cobwebs' off!
 
ToTo Man said:
That's what I meant, - how did you find out the specs for it like THD? Do you have a user manual for it, or did you find the specs on another website?
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I have the 1974 Stereo Equipment Directory with that information in it. The Equipment Directories were published by the same folks that published Stereo Review. They contained a very brief write up on just about all the audio equipment available in the year they were published. The Directories are very handy for looking up information about vintage equipment. Occasionally they show up on the popular auction site.
 
I don't think the signs are encouraging. I switched it on this morning and got startled by loud distorted crackling noises coming from the right channel. So, I switched it off, back on, and the loud crackles came back. I left it on for 30secs or so to see if they diminished but they didn't, so I switched the whole thing off just in case I was running the risk of damaging the speakers. Looks like this poor little guy is in need of repair. I've thought about handing it into my tech, but it is a BIG job to replace all the caps, and at an hourly rate of $50 labour charge, I can't see it being worth it. Oh well, you win some gambles and you lose some, and to be honest $8.75 is not much of a loss anyway. I won't throw the unit in the trash or anything, - it's much too pretty and well-built to do that to it! It'll either go into storage or I'll try and find a buyer who likes a project to tackle!.....
 
Did you check out the other two channels? Are they noisy too? If not, you could just have the one bad channel repaired. You do not have to replace all the capacitors. It might be worth a shot.
 
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