Sharp GF575 Loss of sound

[Mark1892]

While I wait for parts for a GF767, I have started on a GF575 that I picked up as 'not working' recently. Cosmetically it's in good condition, Tuner tunes in and cassette mechanisms work as they should be but there's no audio from the speakers or headphones. The speakers work as there's dirty switch clicking etc when selecting functions. I had a close look at all the boards then I noticed a bulging cap underneath on the ext.speakers board that also feeds the speakers, microphone and headphones. Nothing else appears to be bulging or blown so this looks like the prime suspect. Anybody confirm what this one is for?

 

[floyd]

I know the cap with the crud on top is definitely bad and it could be the problem.
.

 

[Fatdog]

I know the cap with the crud on top is definitely bad and it could be the problem.

Yeah, at this point, it doesn't matter what the capacitor is for... it needs to be replaced.

 

[Mark1892]

Yes definetly, it's the first thing to do. Hopefully audio will be restored once replaced. Will get it out and see if I can see the values.

 

[Mark1892]

Hopefully a simple fix.

 

[Mark1892]

Just a little update on this one as its been a while since the original post. I've changed a couple of blown caps and given it a thorough clean, changed belts etc. I still couldn't get any sound out of it except a little bit of hissing which went up and down with the volume control and also a popping noise from the speakers when moving the function switch to aux, tape and radio.

I put it away for a couple of months then on Sunday night I thought I'd dig it out and have another look at it. I plugged it in turned in on and selected radio and it was working perfectly fine on all functions 😎.

I continued to use it for about an hour until my wife shut one of the drawers of the unit it was on. Not sure if it was coincidence or whether the movement dislodged something again. So now back at square one 🙄

It did sound lovely when it was working mind 😎😎😎

 

[Mark1892]

Looking for suggestions again on this one.

I've got sound now and again in all modes but then it will drop out and all I can hear is hissing through the speakers. Sound might return for an hour or so then drops again.

All switches have been thoroughly cleaned and a couple of bulging caps replaced.

When switching from radio to cassette and line in I get a loud thudding / clicking through the speakers if the dubbing switch is in the off position. If the dubbing switch is in high speed or normal, then switching is silent, just the continuous hissing through the speaker.

If I have tape selected then I also get the loud thudding / clicking when I switch from normal dubbing to off and vice versa.

If I turn the volume right up I can hear the cassette playing very faintly. When the sound is there as normal its very clear and all volume, bass, treble, dolby, tape selector and stereo controls work as normal.

I'm scratching my head with this one. Sound familiar to anybody?

 

[docs]

It does sound like a cap issue to be honest. It is entirely possible something else blew as a result of that cap going poof.
Often with an intermittent issue like this you might just need to test some of the components around the one you replaced.
Try not to get confused with other symptoms when it is in a state of not providing the volume it should because it could just be a knock on effect rather than a cause.

Also, the capacitors you replaced, you need to explain which they were and if you don't have a service manual you need to find one and check those caps in the manual.

 

[Mark1892]

Spot on Docs, the volume returns and can be controlled no problem with the sliders when the sound returns. Thinking the same as you that I need to replace one or all the caps on that board. The other one I replaced was a 16v 1000uf next to the tall one in the pic.

Struggling to find the correct manual as the only one I can find is for the 575Z and mine is the 575E. Similar board layouts but just a tiny bit different 🤔

Just thinking out aloud here but before I changed that leaking cap I had no sound at all, I replaced it with an identical cap from an old GF-555 and it has improved it but maybe that was on its way out too. I'll start with fitting a new one of them first then all the others on that board if no luck 👍

 

[Superduper]

#1, do thorough cleaning with electronic contact cleaner on all switches, controls, bar switches, etc.

Then & only then, with unit open, operating, use a plastic tool, chopstick, or other non-conductive jig & pull/push on all cables, connectors, slightly flex pcb, tap around, etc. the goal being to search for and identify any areas of poor connections.

 

[Mark1892]

Superduper, I've done all your first suggestions a few times already but will do it again when I strip it down before changing anymore caps.

 

[BoomboxLover48]

I had the same issue with the Sharp GF508, the Japanese cousin brother of Sharp GF9696. It was a broken solder on the PC board.
Do all you can like Superduper suggested.
It drove me nuts.... when I press the heat sinks of the amp chip sound will come and when I release it will go. Then no sound at all. When I flex the board a little everything worked. I went and looked behind the main PC board and finally found the broken solder joint.
~Royce

 

[Superduper]

Which is why I suggested to wiggle and flex the board. It sounds like whatever issue is there is intermittent, and doing these usually will cause the condition to manifest. If you find the spot where it gets better or worse, then you've found the area of concern. Flexing the board often helps to expose poor or fractured solder connections or pcb traces.

 

[Mark1892]

Thanks Royce and Super, I'll give that a try tonight and report back, hopefully good news.
Mark

 

[Mark1892]

Just stripped it down about to try what Superduper suggested and thought to myself I've never tried the phono switch at the rear. Line in doesn't produce any sound but when I switch to phono I get distorted music, I have an attenuator inline but it still remains distorted.

Edit: With the aux lines in the input and switch set to phono, I get distorted music even though I'm using an attenuator. If I plug the aux lines in to the line out sockets I have crystal clear music. Is it normal for a line out to able to work the other way? 🤔


Off to probe some more....

 

[Superduper]

Ok, if you inject at line-out rather than line-in, you've just bypassed 1/2 of the circuitry in your boombox as the line-out signal is tied to the point just before the tone controls section. No, plugging in your signal at line-out didn't magically fix anything, you just figured out a way to bypass everything. I'm also skeptical now that you've done a thorough job cleaning. I think it's a possibility that if you thoroughly flood and vigorously work that line/phono switch, and the RCA jacks, you'll find that line-in might just begin to work again.

 

[floyd]

Check the external speaker jacks and switch .these can wreak havoc in these sharp boxes.

 

[Mark1892]

I'm also skeptical now that you've done a thorough job cleaning. I think it's a possibility that if you thoroughly flood and vigorously work that line/phono switch, and the RCA jacks, you'll find that line-in might just begin to work again.

Umpteen times with servisol and deoxit and operated the switch hundreds of times but I'll give it another good dousing tonight and work it some more.

I probed and prodded all wires, switches, connections and flexed the boards last night with it turned on with a wooden skewer and it did nothing different. Another thorough clean/flooding tonight then I'll take it from there. Thanks

 

[Superduper]

Well, we can only offer guesses of the most common problems based on what we hear from you, and the symptoms reported. Since you can get good audio from the line-out point in the circuitry, but you can't get the same from the line-in point, there is obviously an issue between those points. This is where a signal tracer, oscilloscope or some equipment would be most useful. If you don't have those or the necessary skills to make the most of them, then this might be the point where you simply just replace all the caps (since you've already found some bad caps and they are all the same age), and redo all the solder joints and hope for the best.

 

[Mark1892]

Well, we can only offer guesses of the most common problems based on what we hear from you, and the symptoms reported. Since you can get good audio from the line-out point in the circuitry, but you can't get the same from the line-in point, there is obviously an issue between those points. This is where a signal tracer, oscilloscope or some equipment would be most useful. If you don't have those or the necessary skills to make the most of them, then this might be the point where you simply just replace all the caps (since you've already found some bad caps and they are all the same age), and redo all the solder joints and hope for the best.

Thanks Superduper, greatly appreciated advice as usual. 👍