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SOLVED - Gf-777 loud hum and 'galloping' sound


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#1 Concrete Apple

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Posted 23 August 2018 - 04:13 AM

Hi, 

 

I just bought a GF-777. It is in beautiful condition but something is not right inside. When I switch it on the power light turns on accompanied by a loud hum. If I turn the volume up, even a little bit a loud repeated 'galloping' sound is produced. This happens irrespective of which input is selected. I have attached a video which shows this best. 

 

I hope someone here has encountered this before and that it is an easy fix.

 

Any help would be greatly appreciated in diagnosing and repairing this piece of audio history.

 

Thanks!



#2 docs

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Posted 23 August 2018 - 04:36 AM

First thing to do is to clean the record bar of the tape decks.

Alternatively, without needing to open it, if the recording deck works, pop in a blank tape and hit record and stop a few times in quick succession to see if it has any effect on the symptoms you see.



#3 Concrete Apple

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Posted 23 August 2018 - 05:33 AM

Thanks. The problem/sound is there even when the input is set to radio or line in and no other sound can be heard on either of these inputs. Could a dodgy tape head override all the other inputs?

#4 docs

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Posted 23 August 2018 - 06:55 AM

The record bar is a common component for all inputs in some cases and whenever there are odd/loud noises from the speakers this is the starting reference point.

The record bar is not to be confused with the deck play mechanism, it is a large switch which becomes engaged when record is pressed and often all audio inputs traverse that switch thus affecting audio output when it has become dirty/corroded/unused etc. I think there is a thread on here detailing the record bar.



#5 BoomboxLover48

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Posted 23 August 2018 - 09:57 AM

Like Dave explained above you can clean the long record bar switch indicated in the pic with Deoxit. Squirt it from both sides of the long record bar, the holes you  see from the front and manually push it from one end (the right side) at least 30 times. The bottom of the switch is closed fit to the fiber board holding connections on the slide contacts inside. You have to get Deoxit inside through the hole on the metal part, or from the ends of the switch to get the deoxit inside. 

 

~ Royce

Attached Files



#6 Concrete Apple

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Posted 23 August 2018 - 11:45 AM

Thank you so much both of you. I’ll start with the less invasive method and then move on from there and see what gives. Very helpful.

#7 Stuzy

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Posted 23 August 2018 - 12:17 PM

Hi

 

Once back is off unit its easy to see - access. As guys say, this is the place to start.

 

Get stuck in  :clap:



#8 Hisrudeness

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Posted 23 August 2018 - 12:40 PM

Bad earth/ ground?

#9 Fatdog

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Posted 23 August 2018 - 01:40 PM

Here's a post regarding the record bar:

 

https://boomboxery.c...ch-bar-example/



#10 Concrete Apple

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Posted 23 August 2018 - 04:32 PM

Thanks all. The repeated record/stop didn’t work. Hitting record didn’t change the tone of the hum however. I should note that at the moment no sound whatsoever is produced on any of the settings apart from the hum and clicking. Will have to take a look inside on the weekend.

#11 hopey

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Posted 23 August 2018 - 06:38 PM

Can I suggest cleaning your Volume (Knob) Potentiometer? 



#12 Concrete Apple

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Posted 24 August 2018 - 04:07 AM

It looks like the video I intended to attach at the start wasn't attached. I'm sorry, here's a google drive link. It hopefully makes the problem much clearer. 

 

I opened back to have a peek- though must get some Deoxit to do what @BoomboxLover48 suggested.

 

Two things stand out. Photo one: Compared to BoomboxLover48's photo it looks like some plastic latch is missing. And from what I can see here the white vertical plastic cylinder looks like it should be held in the metal U shaped clasp next to it. Or something should be, else it's a piece of redundant design which seems unlikely in a box like this. 

 

Photo two: The other is this small piece of black plastic that was loose inside. Anyone know what it is or where it came from? It's about 1.5cm/0.5" in length. 

 

Thanks!

 

Also - how does one attach images on this forum directly? Can' seem to find an attach button on this editor. There's 'My Media' but even from within there I can't seem to add photos. I am sure I am missing something obvious. It could be because I am new to the forum.



#13 MyOhMy

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Posted 24 August 2018 - 07:02 AM

Also - how does one attach images on this forum directly? Can' seem to find an attach button on this editor. There's 'My Media' but even from within there I can't seem to add photos. I am sure I am missing something obvious. It could be because I am new to the forum.

 

Click on 'More Reply Options' (bottom right) rather than typing directly into the reply box.  :yes:



#14 Concrete Apple

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Posted 24 August 2018 - 07:19 AM

Excellent thank you. :thumbsup:  Here are the photos and video attached properly (I hope).

Attached Files



#15 docs

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Posted 24 August 2018 - 07:35 AM

Hmm, I can't remember the inside of a 777 completely but you might find out where that is from by studying the schematic and finding the part?

 

Just looking at the video I would guess at a bad ground at the power source. Does the power socket where you input the cable have a small switch inside? Tried on DC or Batteries? Just for comparison.



#16 Concrete Apple

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Posted 24 August 2018 - 01:01 PM

Hmm, I can't remember the inside of a 777 completely but you might find out where that is from by studying the schematic and finding the part?

 

Just looking at the video I would guess at a bad ground at the power source. Does the power socket where you input the cable have a small switch inside? Tried on DC or Batteries? Just for comparison.

 

Just tried with batteries- unfortunately the problem remains.

 

I'm not sure if this is normal or not but pressing record on the tape deck also turns on the radio, including turning on the light by the power switch (and all the noise..).



#17 caution

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Posted 25 August 2018 - 12:25 AM

This is a common "sleep" feature that lets you play a tape and have it shut off after it finishes.

I once had a flaky cap on a box causing all sorts of crazy buzzing/popping/etc., and since it was in the main power circuit it affected every function. A bad cap in the amp section could potentially do this as well.

#18 muchkusblin

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Posted 27 August 2018 - 03:44 PM

Seems the noise is 50-60 Hz, right? I would also suspect faulty Ground. Will show your video to a couple of tech guys whom i know, they may point to the problem out of their experience.



#19 MyOhMy

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Posted 27 August 2018 - 04:52 PM

First thing to do is to clean the record bar of the tape decks.

Alternatively, without needing to open it, if the recording deck works, pop in a blank tape and hit record and stop a few times in quick succession to see if it has any effect on the symptoms you see.

 

By perchance....................I was playing with a very sad looking, rather beat up Hitachi TRK-9005 and two of the issues it had were a constant humming sound accompanied by a clicking noise of some kind.  I followed your advice and popped in a blank tape and hit record and stop a few times in quick succession to see if it has any effect on the symptoms and it did actually clear up both problems in about 1-2 seconds.   :thumbsup:  :rock:

 

While the TRK-9005 may not be a sought after grail of inter-galactic significance, if there's hope then it's worth saving even if to merely practice my skills.  :yes:



#20 Fatdog

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Posted 27 August 2018 - 05:18 PM

I've been watching this thread because I had a similar thing happening with my GF-777.  I am using the GF-777 as speakers for my computer.  A mechanical "machine gun" sound started coming out of the speakers one day.  I thought it was starting to die, at least one or more caps, so I just decided to live with it until I had no choice but to try and fix it.

 

Well, today the sound wasn't so prevalent, but then I noticed it would get louder then softer.  So, I started working switches, knobs, everything.  Pushing the left cassette keys made the sound quieter.  Odd.  I pushed the right cassette keys - no change.  Touching the left grille made the sound quieter too.  Twilight zone.  So, thinking there's a ground issue with the entire left side, I ran my hand down the left side of the GF-777 while touching it.  The sound disappeared.

 

Okay, I'm really flummoxed now.  I remove my hand, sound comes back.  Then, I had an idea of  what the real problem was...

 

We had recently upgraded our Comcast xfinity modem and the modem was sitting - you guessed it - about six inches to the left of the GF-777.  After moving the modem further away (about 18 inches now), there is no noise.

 

Electronic interference.  Who would have thought?  Never had an issue before that.



#21 Concrete Apple

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Posted 06 November 2018 - 06:52 AM

I've been watching this thread because I had a similar thing happening with my GF-777.  I am using the GF-777 as speakers for my computer.  A mechanical "machine gun" sound started coming out of the speakers one day.  I thought it was starting to die, at least one or more caps, so I just decided to live with it until I had no choice but to try and fix it.

 

Well, today the sound wasn't so prevalent, but then I noticed it would get louder then softer.  So, I started working switches, knobs, everything.  Pushing the left cassette keys made the sound quieter.  Odd.  I pushed the right cassette keys - no change.  Touching the left grille made the sound quieter too.  Twilight zone.  So, thinking there's a ground issue with the entire left side, I ran my hand down the left side of the GF-777 while touching it.  The sound disappeared.

 

Okay, I'm really flummoxed now.  I remove my hand, sound comes back.  Then, I had an idea of  what the real problem was...

 

We had recently upgraded our Comcast xfinity modem and the modem was sitting - you guessed it - about six inches to the left of the GF-777.  After moving the modem further away (about 18 inches now), there is no noise.

 

Electronic interference.  Who would have thought?  Never had an issue before that.

 

I wish a solution like that could have been found for my box. I took it Armstrong Audio in London in the end to have it repaired. It made  the same unholy sound when connected up in their workshops.

 

Just got it back. Apparently it had 3 hairline cracks on 3 different PCBs. Transit damage it would seem. I have attached a photo of the work on one of the boards with the most noticeable new solder along its tracks (near +c809 and  +c825).

 

It is now fully working which is excellent. :clap:  A bit beyond my diagnostic and soldering abilities.. :blush:

 

Thank you all for you help.