Sharp GF-800 Louder Out Of One Channel…

[lucasmertens]

Hey fellow boombox enthusiasts!

This is my first post here. Quite happy to have found a place where people are still passionate about boomboxes from way back when.

So I’ll jump right into it… I have a gorgeous Sharp GF-800 that I bought a few years ago. I’m trying to restore it to fully-working condition. It works quite well actually, but there’s a small nagging issue that’s been bothering me; the left channel is softer than the right channel. It’s not a huge difference (I measured about 4-6dB difference) but it’s enough that it bothers me.

I currently have the system apart and have done the following:

1) I have cleaned all the sliders using compressed air and then a very soft horsehair-bristled attachment on my vacuum cleaner. This got rid of some crackling I’d been hearing but did not fix the main issue.
2) Switched speakers to see if it was localized to the woofer/tweeter units - it isn’t.
3) Tried different inputs (radio, cassette, auxiliary) - the problem still persists regardless.
4) Tried watching the VU meter - the VU meter actually reflects the problem, with the left showing a bar lower than the right.

So with that being said, does anyone here have any idea what might be causing this issue? And more importantly, how I might go about fixing it? I’m not too technologically savvy in this area but I’m not afraid to get my hands dirty if I can learn a thing or two.

Thank you in advance, and thank you for having me on these forums - it feels like I’m at home here!

 

[docs]

Get some contact cleaner and spray/work it into all switches, sliders and ports such as the headphone and speaker sockets and plug in and out of them. You will also want to thoroughly work the “record bar” which is engaged when you hit record mode on the deck. It will be a long thin spring loaded switch. While doing the contact cleaning, test the unit to see if any of the pots/sliders etc affects it.

 

[Wes125]

yeah as docs says.Get some contact cleaner and spray..compressed air wont make it any better apart from blowing out the dust

 

[lucasmertens]

Get some contact cleaner and spray/work it into all switches, sliders and ports such as the headphone and speaker sockets and plug in and out of them. You will also want to thoroughly work the “record bar” which is engaged when you hit record mode on the deck. It will be a long thin spring loaded switch. While doing the contact cleaning, test the unit to see if any of the pots/sliders etc affects it.

yeah as docs says.Get some contact cleaner and spray..compressed air wont make it any better apart from blowing out the dust

Thank you both very much for the suggestions, I appreciate your time and assistance.

Using 64% Isopropyl (the highest concentration readily available at stores around my area, though I do have some 100% stuff on its way in the mail) and with the system unplugged, did the following:

- Sprayed it inside all the switches whilst working them back and forth/off and on.
- Sprayed it inside the 3.5mm and 6.3mm jacks (for the speakers and microphone/headphone inputs/output respectively), then using 3.5mm and 6.3mm plugs, worked them gently back and forth and all around the jacks to cover as much of the internal area as possible.
- Gave the record bar (which judging from the service manual is what the “dubbing start lever” is connected to) a thorough dousing with the isopropyl and worked it back and forth numerous times.
- Sprayed isopropyl on the RCA jacks and using an RCA plug, worked it into there as well.
- After doing all of the above, I used my air compressor to blow out any excess dust/particles that the isopropyl may have lifted and then allowed it all to dry for a few hours before plugging it back in to test.

Sadly, despite all that, the problem persists. I removed the cassette decks and disconnected the tuner module from the power/amp board, and using an RCA input, was able to determine that the problem still occurs…

I’m not sure what to do next… Any further guidance would be greatly appreciated.

 

[Wes125]

put radio on fm station and see if both of the vu lights are reading the same as this..if the lights are down on one side then the problem is in the preamp section..if they reed level then problem is is main amp...but thats not always the case as some vu lights have an adjustment pot to level them up..DONT TOUCH THAT POT ADJUSTMENT. it will not make the other speaker any louder

 

[goodman]

If I still remember, this Sharp have Line out.
Try to connect to some Amplifier and check L and R Channels.
If they are balanced, problem is into power amp of your Sharp.
If they are unbalanced, problem is on another place...
You must find service manual and trace audio signal.

 

[Wes125]

well heres the service manual if u can understand these

 

[hopey]

well heres the service manual if u can understand these

Thanks Wes125 I placed a copy in the manual section

 

[lucasmertens]

put radio on fm station and see if both of the vu lights are reading the same as this..if the lights are down on one side then the problem is in the preamp section..if they reed level then problem is is main amp...but thats not always the case as some vu lights have an adjustment pot to level them up..DONT TOUCH THAT POT ADJUSTMENT. it will not make the other speaker any louder

If I still remember, this Sharp have Line out.
Try to connect to some Amplifier and check L and R Channels.
If they are balanced, problem is into power amp of your Sharp.
If they are unbalanced, problem is on another place...
You must find service manual and trace audio signal.

Thanks for replying Wes & Goodman,

I’ve been doing a little experimenting (within the realm of safety - I have not and will not touch any pots on the Sharp unless I’m absolutely sure I know what they’re for).

Wes, I looked very closely again at the VU meter in FM radio mode, and whilst the two channels both light up and appear to be level on first glance, they actually aren’t - one is ever so slightly out-of-sync with the other. I tried this with all other input sources as well, with the same results. Does this mean that my preamp is most likely the source of the problem?

Goodman, I don’t actually have any separate amplifiers to do this with - I have several boomboxes, but no dedicated amps! But I get the impression the results would probably be the same, as it seems the problem persists regardless of what I do…

As for my “experimenting” (if you could call it that!) I connected both test leads of my multimeter/voltmeter to a 3.5mm to 3.5mm cable, with the other end of the cable going to the left, then right speaker outputs. As you can see in the attached images, the voltage from the left speaker output is considerably less than that of the right speaker output. The volume was on the lowest setting for each of these measurements.

I’m not sure if that’s a help to anyone here, but I figured it couldn’t hurt to attach the results anyhow…

 

[Reli]

The issue is often a dirty function switch that switches between radio, tape, aux, etc.
The stereo switch is also sometimes the problem.
Followed by the record bar.
I don't think isopropyl works as good as actual contact cleaner like DeOxit

 

[Radio raheem]

try on headphones see if the sound is equal, sharp speakers are known to fail

 

[Radio raheem]

if it's fine on headphones try the speakers on another radio

 

[Wes125]

if it sounds level on the headphones try what Radio raheem says..you might have a dodgy speaker..the trouble with all these if's and but's and try this.. with us just texting back & forth on here. we i cant get the true picture with whats going on with it..now your showing us meter readings..now how are u doing this..is there music coming through whats giving u these reading. coz it it is. thats no good doing it that way. all u need is the amp on with no sound at all coming from speakers..just the amp carrier wave u need. then that will tell u on that meter if its down on one side

 

[hopey]

The issue is often a dirty function switch that switches between radio, tape, aux, etc.
The stereo switch is also sometimes the problem.
Followed by the record bar.
I don't think isopropyl works as good as actual contact cleaner like DeOxit

Deoxcit is 70% is alcohol. You should start at the Potentiometer's as they get a lot of work. If the channel was lost it would point to the mode switch.

 

[lucasmertens]

The issue is often a dirty function switch that switches between radio, tape, aux, etc.
The stereo switch is also sometimes the problem.
Followed by the record bar.
I don't think isopropyl works as good as actual contact cleaner like DeOxit

That’s what seems to be the case most of the time, but in this instance I’ve thoroughly worked all the switches, jacks, etc… You’re definitely right about the DeoxIT though, from what I’ve read, it’s pretty awesome stuff. I’ll have to invest in a can soon

try on headphones see if the sound is equal, sharp speakers are known to fail

That’s true, I remember when I plugged in my Sharp WQ-T282, I was so pumped… Only to have the foam surrounds on the woofers literally fall apart seconds later!

But I’ve tried switching the speakers and the problem still persists on the left channel only, so I know it definitely isn’t the speakers this time around.

if it sounds level on the headphones try what Radio raheem says..you might have a dodgy speaker..the trouble with all these if's and but's and try this.. with us just texting back & forth on here. we i cant get the true picture with whats going on with it..now your showing us meter readings..now how are u doing this..is there music coming through whats giving u these reading. coz it it is. thats no good doing it that way. all u need is the amp on with no sound at all coming from speakers..just the amp carrier wave u need. then that will tell u on that meter if its down on one side

It isn’t level when I plug headphones in… I’m certain it isn’t the speakers. Unfortunately, I don’t think this is something I can fix this time Thank you for offering your help, but I think I’m probably at my limit here in regards to what I can do for the problem, so I’m just going to find someone locally who I can pay to repair the issue for me. If I were to go any further, I’d probably end up breaking something or messing it up even worse, then I’d really be kicking myself!

Thanks to all who tried to assist me anyway, I appreciate your time and patience. This community rocks!

 

[goodman]

The multimeter test proves that the output level is different for the two channels.
Here is a picture from the service manual:

In red is the entire sound path (from left to right):
1. in yellow is the function switch (cassette-radio-input)
2. line amplifier;
3. dolby scheme - green arrow - line output in blue.
4. graphic equalizer;
5. volume control;
6. final amplifier;

There can be a problem in any module.
You can connect the line output to the line input of another bomboox in your collection.
If the sound is balanced - then the problem is from block 4-5-6;
If the sound is unbalanced - then the problem is at the beginning of block 1-2-3 ...
When the problem is localized - it will be easier to find a solution.
Good luck.

 

[caution]

Well done, goodman!

 

[lucasmertens]

The multimeter test proves that the output level is different for the two channels.
Here is a picture from the service manual:

In red is the entire sound path (from left to right):
1. in yellow is the function switch (cassette-radio-input)
2. line amplifier;
3. dolby scheme - green arrow - line output in blue.
4. graphic equalizer;
5. volume control;
6. final amplifier;

There can be a problem in any module.
You can connect the line output to the line input of another bomboox in your collection.
If the sound is balanced - then the problem is from block 4-5-6;
If the sound is unbalanced - then the problem is at the beginning of block 1-2-3 ...
When the problem is localized - it will be easier to find a solution.
Good luck.

Whoah, thank you Goodman! Perhaps I won’t need to find a repairer after all

When I get some spare time this weekend, I’ll study the schematic you provided, test the line out and see if I can’t find just where the problem lies.

Seriously, a massive thank you again for taking the time to outline those blocks and detail them too, I really appreciate the details as I wouldn’t have been able to identify and isolate those on my own (I’m pretty useless when it comes to identifying components in circuit schematics ).

I’ll let you know how it goes this weekend!

 

[Wes125]

i remember one of my aiwa music centres was down on the left output. i replaced 7 small caps on the pre amp board and that sorted it out

 

[goodman]

Whoah, thank you Goodman! ... I’ll let you know how it goes this weekend!

I'm glad that I can help you. Keep us posted.