Sharp GF-575E Audio Distorting pick up failure

[Christopher1389]

Sharp GF-575E 1983

Hello, everyone. I'm new here and I have recently just bought this sharp GF-575E On Facebook marketplace. The guy told me when I bought the unit. It had an issue when the audio would cut out after an hour. It would play tapes fine and the radio does work, but after an hour the audio Would disappear. So I asked the guy has any capacitors or transister's been replaced in the unit He said no but then said 2 had been replaced. So anyway I bought the unit and took it home Plugged it in and he was right. No audio So I waited a day And then I decided to open it up.
And what a mess it was Well it wasn't too bad but Most of the Screw posts have been snapped, and the tweeters were unsoldied.
Also The tweeter brackets that hold them on to the face plate we're snapped, well, one was.

So anyway Just wondering, if anyone can help me with this issue where the Audio is barely being picked up.
From The tape and radio tuner It's like the unit is not able to hear the cassette being played or radio And when it comes on it's distorted

 

[Fatdog]

Welcome aboard, Christopher! It's beginning to sound like a previous owner tried to fix the VZ on the cheap and only made it worse. I don't own a VZ, so I'll let members more knowledgeable than me help with specifics, but... in general, here would be my "starter" advice:

1. Download the GF-575 service manual from the Boomboxery Library (link in main menu). Use that to check factory capacitor ratings against what is inside the VZ. Yes, it will be tedious.
2. Clean all switches, faders, and knobs with a good contact cleaner like DeOxit. Keep in mind that to properly do so will mean you might have to disassemble more of the VZ to get access to cleaning holes.
3. Locate the record bar for the cassette player. The mention of distortion "could" indicate a dirty bar. See this thread for what the record bar looks like (it also has instructions/suggestions for cleaning): https://www.boomboxery.com/forum/threads/record-switch-bar-example.28289/

Try all of that and let us know how it goes. Allocate at least a few hours for all that.

 

[Christopher1389]

Welcome aboard, Christopher! It's beginning to sound like a previous owner tried to fix the VZ on the cheap and only made it worse. I don't own a VZ, so I'll let members more knowledgeable than me help with specifics, but... in general, here would be my "starter" advice:

1. Download the GF-575 service manual from the Boomboxery Library (link in main menu). Use that to check factory capacitor ratings against what is inside the VZ. Yes, it will be tedious.
2. Clean all switches, faders, and knobs with a good contact cleaner like DeOxit. Keep in mind that to properly do so will mean you might have to disassemble more of the VZ to get access to cleaning holes.
3. Locate the record bar for the cassette player. The mention of distortion "could" indicate a dirty bar. See this thread for what the record bar looks like (it also has instructions/suggestions for cleaning): https://www.boomboxery.com/forum/threads/record-switch-bar-example.28289/

Try all of that and let us know how it goes. Allocate at least a few hours for all that.

Hello thanks for the advice @Fatdog it definitely does Look like the guy did not take any care in his work. The previous owner told me that he had already sprayed the switches with dioxit But I did it again with no luck.

So recently I managed to acquiye the schematics and service manual for the unit
And I remember him telling me
That he had replaced a capacitor or 2
In one of the boards so I had look round and found this board. The schematics Told me
That the audio runs though here and it connected to the power switch. So could this be the audio Amplification power board?

Also I noticed that there is some corrosion.
On one of the pins of this Regulator And one of the Capacitors branded nichicon (CSM) Feels a little bit bulged the one with blue one top Also, the one next to it is the same value Looks a bit sad.

 

[Ken]

Do you own and know how to use a multimeter?

 

[Christopher1389]

Do you own and know how to use a multimeter?

Yes I do I have a analogue and a digital one

 

[Fatdog]

From the picture, that one leg on the amp looks bad with that much corrosion. For me, that board would definitely be a starting point. Use a multimeter to measure against values listed on the schematics/service manual. I bet continuity is buggered for the amp - but just a guess.

 

[Christopher1389]

From the picture, that one leg on the amp looks bad with that much corrosion. For me, that board would definitely be a starting point. Use a multimeter to measure against values listed on the schematics/service manual. I bet continuity is buggered for the amp - but just a guess.

OK so a little update I have recapped the amplifier board And took them bulged capacitors out and then put the unit back together and powered it up and sound came back for a minute or two it sounded much better and louder BUT THEN it slowly faded to static and now it's stuck on this static sound on all inputs radio cassette and line in
Also continuity is fine with the power amplifier IC HA1392

 

[Reli]

Service manual says the power amp should actually be a Toshiba TA7246AP

 

[Huffers]

Hi Christopher1398
Reli is correct. IC601 is not the audio power amp. It’s the LED indicator amp. The Audio amp is IC701.
Also the manual says that IC601 should be IR2E01
Which is an LED driver, you are correct HA1392 is an audio amp and can be found in several Sharp boxes.

 

[Huffers]

Hi Christopher1398
Reli is correct. IC601 is not the audio power amp. It’s the LED indicator amp. The Audio amp is IC701.
Also the manual says that IC601 should be IR2E01
Which is an LED driver, you are correct HA1392 is an audio amp and can be found in several Sharp boxes.

Actually just had a look and there are different derivatives of the 575
The 575B & 575Z are as above. However the 575H does indeed use the HA1392 at IC601.
I assume you have the GF-575H version. Probably maki g sure which version you have and have the correct manual just to ensure someone before you has put in wrong components.

 

[Christopher1389]

Hello @Huffers I have the GF-575E which says on the back of my unit. The service manual GF-575E/H so those models must have the some internal components but the GF-575B & GF-575Z must be different. I am trying to look for the datasheet for the ic HA1392 to no avail

Actually just had a look and there are different derivatives of the 575
The 575B & 575Z are as above. However the 575H does indeed use the HA1392 at IC601.
I assume you have the GF-575H version. Probably maki g sure which version you have and have the correct manual just to ensure someone before you has put in wrong components.

 

[Christopher1389]

I video of the static sound I get on all outputs

 

[Huffers]

I video of the static sound I get on all outputs

Interesting. Will see if I can dig out a schematic for the Ha1392. I have had a few of these go in other boxes. sometime they go because the electrolytic capacitors around them on the audio circuit go short and short out the IC.
Although judging by the static I am thinking the main power amp ok (as if it was the chip I don’t think you would get that level
Of audio). I would think that it’s something feeding in before the amp that is causing it.
Maybe try to isolate some of the inputs from the radio cassette, aux. And see if you can remove the interference to narrow down the issue.
The interference sounds like radio interference, does the sound alter at all if you rotate the tuner dial even if only slight? Maybe try isolating the tuner circuit first.
There are also some pre-amps I believe on this box so you could check this out.

A box of this age I would certainly check out the electrolytic capacitors as they have a tendency to fail. You can check with an ordinary multimeter or you can get a transistor test like the LCR-T7 pretty cheap. As well as measuring capacitance (multimeter should have this) they should also be open circuit on a resistance test.

 

[Huffers]

Here is the data sheet for HA1392

https://pl-1.org/getproductfile.axd?id=831&filename=HA1392.pdf

 

[Ghettoman]

i have a couple of GF575's, they have the Hitachi HA1392, then i have a couple of GF787 and a GF858, they have the Toshiba Amp, TA7246, in Fact one of my 787's has a bad amp so i just ordered one from Ebay.

 

[Christopher1389]

Interesting. Will see if I can dig out a schematic for the Ha1392. I have had a few of these go in other boxes. sometime they go because the electrolytic capacitors around them on the audio circuit go short and short out the IC.
Although judging by the static I am thinking the main power amp ok (as if it was the chip I don’t think you would get that level
Of audio). I would think that it’s something feeding in before the amp that is causing it.
Maybe try to isolate some of the inputs from the radio cassette, aux. And see if you can remove the interference to narrow down the issue.

Interesting. Will see if I can dig out a schematic for the Ha1392. I have had a few of these go in other boxes. sometime they go because the electrolytic capacitors around them on the audio circuit go short and short out the IC.
Although judging by the static I am thinking the main power amp ok (as if it was the chip I don’t think you would get that level
Of audio). I would think that it’s something feeding in before the amp that is causing it.
Maybe try to isolate some of the inputs from the radio cassette, aux. And see if you can remove the interference to narrow down the issue.
The interference sounds like radio interference, does the sound alter at all if you rotate the tuner dial even if only slight? Maybe try isolating the tuner circuit first.
There are also some pre-amps I believe on this box so you could check this out.

A box of this age I would certainly check out the electrolytic capacitors as they have a tendency to fail. You can check with an ordinary multimeter or you can get a transistor test like the LCR-T7 pretty cheap. As well as measuring capacitance (multimeter should have this) they should also be open circuit on a resistance test.

The interference sounds like radio interference, does the sound alter at all if you rotate the tuner dial even if only slight? Maybe try isolating the tuner circuit first.
There are also some pre-amps I believe on this box so you could check this out.

A box of this age I would certainly check out the electrolytic capacitors as they have a tendency to fail. You can check with an ordinary multimeter or you can get a transistor test like the LCR-T7 pretty cheap. As well as measuring capacitance (multimeter should have this) they should also be open circuit on a resistance test.

OK so I've checked the IC HA1392 and it seems to be OK I also checked the dolby chips and they seem to be fine too.
I'm not quite sure how I would go about isolation outputs. The sound really does sound like radio interference but when the box is switched to cassette it still has the same sound even if I rotate the tuner dial

 

[Huffers]

OK so I've checked the IC HA1392 and it seems to be OK I also checked the dolby chips and they seem to be fine too.
I'm not quite sure how I would go about isolation outputs. The sound really does sound like radio interference but when the box is switched to cassette it still has the same sound even if I rotate the tuner dial

Apologies I am not that familiar with the 575, have you downloaded the service manual you should be able to trace the input singles. I have had a quick look through see if I can work it out. FM seems to come in on connector CNP1, Tape Deck 1 is CNS202 and Deck 2 is CNS201. The line in signal is Connector CNS302. so disconnecting them in turn should remove the input signal and parts of the circuit. For instance disconnecting CNP1 should remove the the whole tuner board, so if that removes the interference then the issue should be on the tuner board.

Try that first to see if any of those removes the interference, hopefully this will narrow down where the issue is.

 

[Christopher1389]

I've just came back from vacation and got to checking the IC chips on the board. Looking the dolby ic TA-7629P as the Audio signal goes through those but I can't find a datasheet for them

I think now the problem is past the selector switch going to the amplifier

 

[Christopher1389]

Apologies I am not that familiar with the 575, have you downloaded the service manual you should be able to trace the input singles. I have had a quick look through see if I can work it out. FM seems to come in on connector CNP1, Tape Deck 1 is CNS202 and Deck 2 is CNS201. The line in signal is Connector CNS302. so disconnecting them in turn should remove the input signal and parts of the circuit. For instance disconnecting CNP1 should remove the the whole tuner board, so if that removes the interference then the issue should be on the tuner board.

Try that first to see if any of those removes the interference, hopefully this will narrow down where the issue is.

Thanks for the advice @Huffers so before I went on vacation I did just that I isolated the amplifier from the tuner and cassette deck and still get the same sound. I then tested the transistors Q181 q183 Just because they are in the path or the audio or circuit
And they tested all OK. So my Suspicion now is the dolby chips TA-7629P But unfortunately, I don't have the datasheet for them

so I tested them and one side doesn't read at all pin 9 10 11 13 14 15 16 and pin 12 is grownd is this right I haven't tested a ic before ? The gray line going into pin 4 is the Playback signal

 

[Tinman]

Did you verify that all of the new caps are installed correctly +/- ?
Are those fusible resistor on that board, if so, did you check them?