Sylvania RS-4744 no sound

TTWB

New Member
I took a chance and grabbed a Sylvania RS-4744. To me, the quality of most things, including radios is like pornography. I can't necessarily describe it, but I know it (quality) when I see it. I realize this Sylvania isn't a Marantz, but it seemed to be good quality, closer to the size receiver I was looking for, and fairly clean. We couldn't get sound out of it at the store, but I still felt is was worth the $35 I paid. Fingers crossed...

So, it doesn't matter if I try radio, Phono, etc., all I can get is an initial "pop" to the speaker, but then no sound. The pop, i believe, tells me that I have all buttons/switches set appropriately. Not that it matters, but all lights and meters appear to work correctly as well. There is a breaker, which also appears to function correctly. I have (want) to believe it's something simple.

I have a Realistic receiver that wasn't behaving and quick shot with Dexoit did the trick. A perfect small unit for my daughter's turntable. Looking at this Sylvania, I removed the front plate, etc. and man it just doesn't look like the pots are easily accessible.

I also connected headphones. With headphones on, and volume cranked all the way up, I could faintly here FM. Couldn't hear anything on AM or the Phono though.

When turning on, I can hear what I believe is the relay. When turning off, I also hear what I believe is the relay.

Any ideas what to look at?
 
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You have a vintage piece tha't going to require some work, but if you are
careful, you will have a nice piece. Ususal candidates in this case are
dirty switches, bad contacts/solder joints and faulty power supply/protection
circuit since both channels affected.

Deoxit the controls, there is a sticky that explains how.

Keep things simple, plug a CDP/iphone or whatever into a TAPE IN and
check for sound, this rules out the tuner and phono circuitry.

Try running the receiver as a separate, run RCA cables from the pre-out to
another (power) amp. The other test is to provide external input (preamp, iphone,,)
to the MAIN-IN of the receiver. The relay click is a good sign
 
Thanks MBZ. I Deoxit'd the volume and balance and the Mute. Well, as best I could. The others I can't really get to. I have the top and bottom off, but there isn't much access.

Funny side note; The metal plate that all the switches are mounted through, is etched and labeled, Treble< base whatever. Nice, for when the faceplate is removed. However, the Balance is actually labeled Bass. So there are two Bass, one Treble and Volume. That guy had ONE JOB TO TO DO!

Anyway, I did try the headphones, I tried Phone and tried Tape 1 and Aux with a CD player as well.

With a CD player hooked into Tape 1, it played at normal level, but almost immediately began to fade down, then out. I couldn't get back, UNTIL, I turned off the receiver, then back on. Same thing; strong volume, then fade to black ; (
 
Anyway, I did try the headphones, I tried Phone and tried Tape 1 and Aux with a CD player as well.
Did you try iphone connected to Power Amp input RCA's. The amp can be used as either a integrated, pre-amp or power amp.
There's RCA's at the back and probably joining links that go from pre-out to main-in. The other test is to connect the pre-out
to another power amp, the idea is to localize the problem as either a pre or power amp issue.

With a CD player hooked into Tape 1, it played at normal level, but almost immediately began to fade down, then out. I couldn't get back, UNTIL, I turned off the receiver, then back on. Same thing; strong volume, then fade to black ; (
Probably a power supply issue, have you located the service manual?
 
I haven't found a manual yet. I guess I have to be a member at Hifiengine?

I see one section: PRE -- AMP TO AMP. Underneath that there are two sets of RCA. Two on Left, top and bottom, and two on Right, top/bottom. The top RCAs have an L between the and the bottom two have an R between them. So, I get the Left and Right. The top are jumped (links) to each other, as are the bottom. But how do I know which is input and which is output? Are the top/bottom RCAs preamp?

Not sure it matters, but the PRE seems centered over the two RCAs on the left. But the four RCAs seems to be one section, so it's not very clear.
 
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hifiengine requires that you register so it can confirm that you are
not a "robot"/cyber attack etc... it is safe, no spam etc...
hifienging only has the sales brochure

I took a chance on
http://www.vintagesylvania.net/?page=downloads&category=service_manual
often an easy way for virus download. Download appears safe, service manual
is of reasonable quality. Suggest download it, needed for troubleshooting.

Looking at the 4 RCAs "PRE - AMP TO AMP", the 2 on the left are the output
of the preamp stage, L&R channel, the 2 on the right are input to power amp
stage. The joining links simply connect the preamp to the power amp.

Suggest remove the joining links then connect your ipod/iphone/ixxx to
the power amp input RCAs (on the right), set volume to minimum and slowly
increase, check sound through speakers or headphones. This tests the power
amp stage.

The other tests involves connecting from the pre-out RCAs (on the left)
to the power amp stage of another amp. Do you have another amp prefer with
pre-out/main in RCA's.

Would be nice to run a basic health check at some stage, check power supply
voltages, bias, dc offset. Do you have a suitable multimeter? Are you comfortable
working on live electronics/lethal voltage inside.
 
Thanks for the manual link! I was going to join today. Just to clarify, when the volume drop,s the unit does still stay on. I figured you knew that, but wanted to confirm. I wrote, "fade to black" and simply meant that the music faded, not the unit.

Yes, I do have a Kenwood Eleven II. Man, these things aren't convenient to move around. I had no idea how big that beast was when I got it. In fact, it's why I grabbed the Sylvania. Just wanted one vintage piece, so I might sell off the Eleven II, but we all know how that usually goes. It's really clean and other than one phono bulb out, everything seems to function, except, you guessed it, the timer switch. It's physically broken (like that when he shipped it), but fortunately the unit powers on and work without any issue. The output is just ridiculous on those things. Ugh..we'll see. Anyway...

I am comfortable with DMMs, soldering, etc., and have some HAM equipment I've tested, repaired for minor issues, etc. The Kenwood 530S I have can store hundreds of thousands of volts, so I'm careful with anything I open up. I was hoping for a Deoxit shortcut on this Sylvania :( We have one bathroom torn out and another to do. I'm not doing the remodel myself this time, but it's amazing how much work "not" doing the work is. I was hoping to get this thing running and put it aside or replace the Eleven II. I might pack it up for now, we'll see how today goes. We have so much stuff jammed in various rooms, I'm not sure I could fit these two receivers in one room right now! You know deal, two kids, both parents working, oh and toss in a sick dog along with the home repairs.

The manual will help a lot. And you providing a basic direction to go is exactly what I was looking for as well, so I appreciate that. On the inside of the cover Sylvania stapled a diagram of resisters, which was a good idea.
 
A quick update. I connected my Iphone to the power amp input. No sound, other than the initial pop. However, I turned off the receiver. Pushed each of the speaker breaker buttons and the main breaker button - none of them felt like they reset, so I don't believe they ever tripped. Turned the unit back on, heard mostly music/crackling for 5 seconds or so, then sound fades out. Turned off the receiver, this time did NOT push any breakers, and same result; crackling/music, then sound fades out. Again, I don't believe the breakers are related to the issue, nor are they tripping, as far as I can tell. Basically the input to the power amp is the same result as trying to play FM, Phono, etc.

there's no way I'm carrying that Model Eleven down to my bench for a pre-out test! I'll see if I can make some room next to the Eleven and connect them.
 
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Appears to be a power amp problem, power supply the likely culprit, will try and track down some test points for voltages etc...
 
Power supply to the power amps is just unregulated supply after
the main filters. Maybe you have one or more rectifier diodes
down or a failed main filter. Quick and easy voltage measurement
as per the pic, maybe best to measure from the top, diodes are
near the main filters, measure Vdc to GND. Expect it to bounce
up and down. With amp powered off/unplugged you should also
diode test SC506, 508, 510, 512, 514, 516, try in circuit.
 
TTWB - The RS4744 was Sylvanias TOTL receiver with some neat features. The PQ4 feature is a sort of a faux quad option for 2 channel tracks. I sold mine a couple of years ago and haven't found any glamour shots of the inside yet but still looking if it will help. I was fortunate with mine, as it only needed dusting some DeOxit and adjusting the idle current. I do hope you will be able to get your RS4744 running properly, they are worthy of preservation.
 
Well, I'd feel better at my bench, but so far, here's what I have. Unit unplugged, ach of these diodes, in circuit, SC506, 508, 510, 512, 514, 516, tested @ .42 up to almost 1.0, fluctuating. However, when I reverse the test, they climb to @ 2.0, the hit OL. I know they should be OL, so is it normal for them to climb there?

Unit plugged in. I used the Phono Ground screw for Ground. Tested SC508, SC512, SC514, SC516, all tested @ .004V A/C. You wrote Vdc to ground, not sure, did you mean V ac?

Is that Phono ground screw a good ground?
 
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Incircuit component testing has many traps. The MM current can
be divided along alternate paths, also the current can charge up
any nearby caps so the MM reading keeps climbing.

In this case I was looking for a shorted rectifier diode, the 0.42-1V
suggests no short. The OL is just charging the caps.

I wanted to verify the dc voltage at points LL and PP in the sm. See
the highlights for measurement points in post #11. Expecting about
+/-50Vdc. The phono ground screw is a good earth point, you can also
use any black speaker posts (sometimes easier to clip MM probe in)
 
Roger that on the MM current. I would much prefer to be at my bench, but working with my decent DMM, I believe I'm getting accurate readings.

Both SC508 and SC512 tested -112Vdc and 514 tested -117 Vdc. Reverse showed little to no voltage coming through the diode, as expected.

BTW, Sylvania has the best speaker posts for this. You push the button in and slide the probe in horizontally, so it's parallel to the back of the case. Hold the probe very well! Can be a pain when connecting speakers, while you're leaning over the front of the unit, but once in, those wires are never coming out :biggrin:
 
What is your mains voltage, USA 120Vac?
What is the AC voltage stamped on the back of the unit?
Is there a voltage selector switch?
 
USA 120V current
Unit stamped 120 Volts 60 Hertz
No voltage selector switch that I can find.

With plugged in and unplugged, results were the same.

The diodes are bullet shaped (flat on one side and rounded tip on the other).

512 and 508 have a thick grey line on that rounder end, so I decided that was cathode (-).

506 and 510 have a thin grey line on each of their ends, so 2 grey lines on each. Again, I decided that the rounder end was cathode.

I detailed the above, because looking at the results, after rechecking, you'll see that 512 and 508 match, but are different than the matching 506 and 510.

So the diodes are shaped the same, but clearly the cathode and anode are on different ends.


SC512
- 00.1Cathode
-104.2 Anode


SC510
-97.4 Cathode
- 00.1 Anode

SC508
- 00.1 Cathode
-103.3 Anode


SC506
-99.05 Cathode
- 00.1 Anode
 
SC506, 510 anode and SC508, 512 cathode are on the "AC side" so
near zero DC is expected.

The other voltages are about twice what's expected which might
suggest a reference (earthing) problem, however they are all negative.

Spend a few minutes to check the grounding.
Inspect the GND point between the 2 main caps, point ZZ on schematic,
probably a few (4-5?) wires (black?) terminating there, check for solid
connections (tug a little) and inspect solder joints if possible. One
of these (black?) wires probably connects to the chassis. Check this
connection.

Next, checkout the transformer winding. With amp powered off/unplugged
measure resistance between SC506 anode(black probe) and ZZ point (or
shorting link as per pix)

Then measure resistance between SC512 cathode (red probe) and ZZ point

In both cases expect a few ohms, I'm not expect the reading to climb to
OL (cap charge up..) If you have a few ohms then maybe repeat,

Expecting +/-50Vdc.
Measure at SC506 or SC510 cathode, expect +50Vdc
Measure at SC508 or SC512 anode, expect -50Vdc


but connect the black MM probe to the ZZ point or joining link highlighted, ie use that as reference

upload_2018-10-16_9-39-57.png
 
First, thank you so much for spending this much time on MY equipment!!! See my result below in red.

Inspect the GND point between the 2 main caps, point ZZ on schematic, I used both ZZ areas and the results always match
probably a few (4-5?) wires (black?) terminating there, check for solid
connections (tug a little) and inspect solder joints if possible. One
of these (black?) wires probably connects to the chassis. Check this
connection. Checked as best as possible. Wires in there seem tight and clean. I can't seem to find where the ground goes to chassis. Maybe I'm getting tired, but I moved on to other tests and will look again tomoroow.

Next, checkout the transformer winding. With amp powered off/unplugged
measure resistance between SC506 anode(black probe) and ZZ point (or
shorting link as per pix) - SC506 results: .7 to .8 ohms.

Then measure resistance between SC512 cathode (red probe) and ZZ point SC512 .54 ohms? I use ?, because of all the tests I ran, this was the most erratic. Every other test, even after several times on each, was about the same and result were quick. SC512 does settle down at times, but it always took longer and was erratic during the process.

In both cases expect a few ohms, I'm not expect the reading to climb to
OL (cap charge up..) If you have a few ohms then maybe repeat,

Expecting +/-50Vdc.
Measure at SC506 or SC510 cathode, expect +50Vdc - 69Vdc
Measure at SC508 or SC512 anode, expect -50Vdc - 71Vdc

Curious, why did you highlight the area near 514?
 
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