After reading this threat I knew I wanted one.

http://REPLACEMENT ERROR/topic...ox-smokes-the-gf-777

Yesterday evening I found one on the local auction site for 20 euros Happy!

nice you do get some bargains michiel 

Excellent deal for 20 euros, 7 speakers and cool styling, nice score!

Well done Michiel, let us know how it sounds when it arrives.

Thanks guys! I already have it here! Shes already on my desk 

Till now she sounds good, but has some issues. First the power switch didn't work properly. Fixed that. Second I got distortion on the left channel with radio and tape. Gonna be a tough one without service manual, but hope to find the culprit component by tracing a 1000Hz tone. And of course it needs new belts

Time for a good internal clean now. And what I really like is that I found the counter reset button inside the box

ANy chance of a close-up of those speaker clusters?

Heavy box indeed.

The 3 speakers seems to be wired in parallel with usual caps.

How is the Woofer wired? Is there a separate amp?

To me this is the genesis of the boomer type that begot the Hitachi 3Ds - a separate big speaker for handling more bass.

I too would like to know whether that 6x9 has it's own amplifier.

I suspect it does, as wiring a single driver and separate left & right drivers with 2 L&R channel amps would be more than a little difficult, surely?

Nice internal pictures. I like to see how things are built!

What an interesting box this is.  What controls are there to adjust sound?  I mean, is there any scope for dynamic variation between the speakers?

There are just the usual controls, mono/stereo, treble, bass and balance. Unlike the box from the other thread it has no Enviro or Mode switches. These are replaced by a mono/stereo switch and a -10db recording level switch.

Yes, the woofer has its own circuitry. When I turn on the box, the woofers goes on after about 4 seconds after the drivers and tweeters started 

Also found an inspection label with a date; 1978

Today I spend the second day on this box finding the reason for the distortion in the left channel. Compared the voltages of the complete left and right channel. No differences at all  Also redone al the solder joints. 

Next I traced both channels with the scope and the distortion shows up very clearly. Its not random, but it flattens the sinus I feed it and it puts some nasty bulbs to zero on it. It starts direct from the beginning where the line amp gets it's signal. And goes through the whole line to the speakers. When I feed it with a very low voltage signal the distortion goes away and I get a good sinus throu the whole line.

Pretty sure by now that it isn't a transistor or ic and really suspect a dried up cap somewehere in the line amp. Next strategy is to replace/measure all the caps of the left line-amp.

Its a pretty nasty box to work on. Lots of wires, all soldered. And really difficult to reach the component side of the amp board without disconnecting many wires. Well, think its worth it. The more I work on it, the more I start to like this box  

Hey Michieel; I wouldn't rule out an IC or transistor being the cause of this.

Originally Posted by Michiel:

Today I spend the second day on this box finding the reason for the distortion in the left channel. Compared the voltages of the complete left and right channel. No differences at all Also redone al the solder joints.

Next I traced both channels with the scope and the distortion shows up very clearly. Its not random, but it flattens the sinus I feed it and it puts some nasty bulbs to zero on it. It starts direct from the beginning where the line amp gets it's signal. And goes through the whole line to the speakers. When I feed it with a very low voltage signal the distortion goes away and I get a good sinus throu the whole line.

Pretty sure by now that it isn't a transistor or ic and really suspect a dried up cap somewehere in the line amp. Next strategy is to replace/measure all the caps of the left line-amp.

Its a pretty nasty box to work on. Lots of wires, all soldered. And really difficult to reach the component side of the amp board without disconnecting many wires. Well, think its worth it. The more I work on it, the more I start to like this box

Hey Michieel; I wouldn't rule out an IC or transistor being the cause of this.

But wouldn't a broken ic or transistor show up in the voltages? I also measured the voltages while the distortion was going on and there is no difference at all between left and right. There are only two transistors in the line-amp, so I could check them as well 

Also found out that the woofer has his own power amp btw

Originally Posted by Seb968:

Originally Posted by Michiel:

Today I spend the second day on this box finding the reason for the distortion in the left channel. Compared the voltages of the complete left and right channel. No differences at all Also redone al the solder joints.

Next I traced both channels with the scope and the distortion shows up very clearly. Its not random, but it flattens the sinus I feed it and it puts some nasty bulbs to zero on it. It starts direct from the beginning where the line amp gets it's signal. And goes through the whole line to the speakers. When I feed it with a very low voltage signal the distortion goes away and I get a good sinus throu the whole line.

Pretty sure by now that it isn't a transistor or ic and really suspect a dried up cap somewehere in the line amp. Next strategy is to replace/measure all the caps of the left line-amp.

Its a pretty nasty box to work on. Lots of wires, all soldered. And really difficult to reach the component side of the amp board without disconnecting many wires. Well, think its worth it. The more I work on it, the more I start to like this box

Hey Michieel; I wouldn't rule out an IC or transistor being the cause of this.

But wouldn't a broken ic or transistor show up in the voltages? I also measured the voltages while the distortion was going on and there is no difference at all between left and right. There are only two transistors in the line-amp, so I could check them as well 

 

Also found out that the woofer has his own power amp btw

Broken IC's may just go low gain, they may partly work and then fail altogether; Transistors normally just fail. If you pinpoint the exact point at which the signal is getting distorted and the supply voltage rails are fine then changing components in that area could be a good idea. Do you have a circuit diagram for this machine?

Originally Posted by Michiel:

Originally Posted by Seb968:

Originally Posted by Michiel:

Today I spend the second day on this box finding the reason for the distortion in the left channel. Compared the voltages of the complete left and right channel. No differences at all Also redone al the solder joints.

Next I traced both channels with the scope and the distortion shows up very clearly. Its not random, but it flattens the sinus I feed it and it puts some nasty bulbs to zero on it. It starts direct from the beginning where the line amp gets it's signal. And goes through the whole line to the speakers. When I feed it with a very low voltage signal the distortion goes away and I get a good sinus throu the whole line.

Pretty sure by now that it isn't a transistor or ic and really suspect a dried up cap somewehere in the line amp. Next strategy is to replace/measure all the caps of the left line-amp.

Its a pretty nasty box to work on. Lots of wires, all soldered. And really difficult to reach the component side of the amp board without disconnecting many wires. Well, think its worth it. The more I work on it, the more I start to like this box

Hey Michieel; I wouldn't rule out an IC or transistor being the cause of this.

But wouldn't a broken ic or transistor show up in the voltages? I also measured the voltages while the distortion was going on and there is no difference at all between left and right. There are only two transistors in the line-amp, so I could check them as well 

 

Also found out that the woofer has his own power amp btw

Broken IC's may just go low gain, they may partly work and then fail altogether; Transistors normally just fail. If you pinpoint the exact point at which the signal is getting distorted and the supply voltage rails are fine then changing components in that area could be a good idea. Do you have a circuit diagram for this machine?

Nope, I don't have the circuit diagram of the machine. It would make things much easier if I had it. Could make my own by making pics of both side of the board and put them on top of each other with photoshop to make a drawing, but that involves lot of work at the mo. I'm just relaying on the symmetry between left and right now.

The deformation of the signal starts immediately where the line-in wires touch the board. So there is feedback to this point on the circuit. I didn't try to put a signal direct to the power amp yet. The power amp is an ic.

I suspect that a component has shifted properties a bit by time. That would explain a bit why it does work normal with a low voltage signal. And why the distortion is not random. The most obvious part would be a partly dried up capicitor I think. In the vicinity of the firtst signs of distortion are only lots of capacitors, resistors and some transistors.

Will do the trail and error replacement and see what happens.  Have to note that I'm a mechanical engineer, so I have no idea if this is the normal way a electrical engineer would tackle this problem lol 

Originally Posted by Seb968:

Originally Posted by Michiel:

Originally Posted by Seb968:

Originally Posted by Michiel:

Today I spend the second day on this box finding the reason for the distortion in the left channel. Compared the voltages of the complete left and right channel. No differences at all Also redone al the solder joints.

Next I traced both channels with the scope and the distortion shows up very clearly. Its not random, but it flattens the sinus I feed it and it puts some nasty bulbs to zero on it. It starts direct from the beginning where the line amp gets it's signal. And goes through the whole line to the speakers. When I feed it with a very low voltage signal the distortion goes away and I get a good sinus throu the whole line.

Pretty sure by now that it isn't a transistor or ic and really suspect a dried up cap somewehere in the line amp. Next strategy is to replace/measure all the caps of the left line-amp.

Its a pretty nasty box to work on. Lots of wires, all soldered. And really difficult to reach the component side of the amp board without disconnecting many wires. Well, think its worth it. The more I work on it, the more I start to like this box

Hey Michieel; I wouldn't rule out an IC or transistor being the cause of this.

But wouldn't a broken ic or transistor show up in the voltages? I also measured the voltages while the distortion was going on and there is no difference at all between left and right. There are only two transistors in the line-amp, so I could check them as well 

 

Also found out that the woofer has his own power amp btw

Broken IC's may just go low gain, they may partly work and then fail altogether; Transistors normally just fail. If you pinpoint the exact point at which the signal is getting distorted and the supply voltage rails are fine then changing components in that area could be a good idea. Do you have a circuit diagram for this machine?

Nope, I don't have the circuit diagram of the machine. It would make things much easier if I had it. Could make my own by making pics of both side of the board and put them on top of each other with photoshop to make a drawing, but that involves lot of work at the mo. I'm just relaying on the symmetry between left and right now.

 

The deformation of the signal starts immediately where the line-in wires touch the board. So there is feedback to this point on the circuit. I didn't try to put a signal direct to the power amp yet. The power amp is an ic.

 

I suspect that a component has shifted properties a bit by time. That would explain a bit why it does work normal with a low voltage signal. And why the distortion is not random. The most obvious part would be a partly dried up capicitor I think. In the vicinity of the firtst signs of distortion are only lots of capacitors, resistors and some transistors.

 

Will do the trail and error replacement and see what happens.  Have to note that I'm a mechanical engineer, so I have no idea if this is the normal way a electrical engineer would tackle this problem lol 

 

 

An engineer is an engineer mate! Seems to me that you have a pretty good idea of what your doing and electrolytic capacitors are very prone to failure. Replace things sequentialy, step by step and I think you will nail this fault. Good luck!  (Let us know what it is when you find it!)

Thanks Seb! Will let know how things going 

Great, problem solved! One faulty capacitor at the end of the line-amp. Replacing it solved everything!  Hearing it the way it should be, this must have been a real expensive quality box back then! Well balanced that is, with a nice fat bass  Get this box if you see one, you won't be disappointed!

Just noticed this thread -- Congrats on finding this cool box.  I was the one who wrote the other thread.  These boxes put out serious bass at very low volumes......but of course it craps out quickly if the bass knob is high.   And the highs aren't bad either, even though the overall sound isn't as precise as a JVC or Panasonic.

Just curious, what is that sticker on your tape door?

Ow, cool you were the inspirator for this one  Yes, the box puts out a very good bass! It's great to follow the bass line in all sorts of music. Got nothing that sounds like it really.

The main problem with mine isn't the bass that craps out. But it puts out so much bass that the whole radio start to rattle due to the vibrations  Tried to solve it. But then an other parts start vibrating at just a litlle higher volume lol.

Its one of those very special radios that I really like  Do you still got yours?

Those small stickers are left overs from a bigger seal or sticker that was place on the box. When I pulled it off the circle stayed on.

There was something about insurance, a telephone number and a serial number on the complete sticker. I guess it was some sort of vintage anti-theft marking. It looked bad, so I removed it 

Ah I see.  You could try putting Dynamat on the back panel, around the woofer.  Something to stiffen it up a bit.

That wil probably solve it. But I like to keep it original  Like the radio anyway.