Disaster with my gf 777

Hello all.
After miles and miles of loud music with my awesome gf777 yesterday a bad thing happened. After a 8 hour battery session we connected the boombox to a power generator. It worked nice for a while, until one idiot of my friends accidentally moved the power knob on the generator, leaving my boombox overloading. I runned there and disconnected immediately the box from source but it was not helpfull. I retried switching on the box:
The red power light goes on but no sound comes out. Tried from batteries and home source too but same thing, so i exclude a power supply fail. Vu meters doesn't move when radio is on, and no light comes out. If I move volume knob fast i can hear some crackling, so amp is ok too.
I opened the box and checked fuses. They were all ok. I don't have so much experience with electronic parts but i suppose it's a transistor somewhere on the upper side or something like this. My box is in trouble, help me to save it

Blown amp chips X 2 + maybe a blown transformer at the very least is my guess. :-(

Where are amp chips? I'm not very expert in this area

Where are amp chips? I'm not very expert in this area

Take it to a repair shop. If the amp modules are blown, and if as you say, you aren't knowledgeable about such things, then its likely beyond your skills and you might cause more damage than good.

What kind of power generator? One of those gasoline-powered things?

Hi superduper, I read something about you. You're the hero of boomboxes! My father is expert but he is a littlebit old and busy of things to do, so I don't want to hurt him. But you can say tecnical things too, we can understand them. We think that amp chips are okay because the stereo is like lobotomized. If radio tuner is powered on, and i move the knob with tuner meter on, it doesn't move or light something. We guess that a transistor is gone on the "logical" part. No radio, no tape, no line but tapes mechanics moves.

Yes, its gasoline powered

tatto said:

Hi superduper, I read something about you. You're the hero of boomboxes! My father is expert but he is a littlebit old and busy of things to do, so I don't want to hurt him. But you can say tecnical things too, we can understand them. We think that amp chips are okay because the stereo is like lobotomized. If radio tuner is powered on, and i move the knob with tuner meter on, it doesn't move or light something. We guess that a transistor is gone on the "logical" part. No radio, no tape, no line but tapes mechanics moves.

Click to expand...

Ok, that's fine. But the problem could be so many different things, where do we start when you have the boombox and we can't look at it. For example, here are some issues with your description: #1, you said that the power indicator lights up. That's great, suggests that power supply is still ok. But the tape mechanism motor runs directly off the rails so if you have proper voltage coming out of the power switch, I'm thinking that your cassette deck motors should run, but I think you said they do not? You mentioned that tuner does not work. That's fine, but how about other modes? Line-input? We need to know. If you think that a transistor might have failed, then you can try to replace Q110. That is a regulator and it's failure could certainly account for no tuner action. However, I do not believe that regulator controls your deck motors so again, do we have multiple failures, or a single more global failure?

Ok after reading your post again I see you saying that tape moves. So my suggestion is replace Q110 which you probably blew.

Thank you, i will give it a look. Sorry for bad explanation but I'm Italian. I'll explain a little better, describing symptoms:
-Deck works as usual but no sound
-Line in, no sound and no vu meter move, like no source is connected
-Vu meters light doesn't power on even box is on. They are still on -20
-Power On Led is on
-Radio no sound and no capting. If i press vu meter button for tuning nothing happens. So i exclude ampchips because when amp chips are gone only no sounds come out, right?

Blown amps often result in distortion or cracking and not always silence. In this case, a more telling symptom is dead tuner with good power supply. As I suggested, replace Q110 transistor and go from there.

Thank you i will do it.

Electric scheme of Q110

Q110. It looks ok, but going to change it today. If its not this, how do i have to troubleshoot?

https://boomboxery.com/forum/index.php/topic/4499-had-a-disaster-withmy-gf-777-help/

Seems a similar problem. But in this case, the vu meters lights are working. In my case the vu meter has no light and no movement from both channels. Batt/Tuner

Look, you are asking for help and let's be clear, it takes a lot of my/our time to do the homework for you and study the diagram to come up with recommendations and of potential issues based on the symptoms you provide. Let's not waste any of it by speculating on what to do AFTER a recommendation has not yet even been applied.

As for troubleshooting procedures, there is simply no way for us to provide you with a course in circuit diagnostics dynamics 101 in the short course of this thread/forum. You asked for help so please trust the judgement based on the information you've provided us and go from there. If at any time you disagree, you are free to try anything that makes more sense to you since it is, after all, your boombox. But for the moment, just please let's not get ahead of ourselves and suggest we troubleshoot further when we don't even know if that's warranted or needed. It takes time for that, so let's not waste it.

Normally, I would not even recommend replacing that transistor without first doing standard testing. This includes doing VR measurements and compare to the specs in the schematics. Armed with a set of VR measurements, it will go a long way towards finding the source of your problems. You apparently do have the schematic so if you want to know how to troubleshoot, then that is the way. That may seem like it would take an enormous amount of time, and it most definitely would if you don't narrow down the potential problem areas. This is where experience comes in and symptom analysis used to rule out areas that are probably good. In any event, if you want to be sure whether Q110 is good, and how you "should" be starting the diagnosis in this repair, then you would:

#1, check for proper voltage at the power switch.
#2, check for proper voltage at pin#1 of connector CNS/P 801
#3, check pin#1 of CNS/P 1 for voltage, approx 12.
#4, check live volts of B/E/C of Q110.

That's just for starters. Because each check above branches off to a different diagnostic path depending on the results of your test, it could soon get very complicated. So therefore, let's just keep it simple for now.

As to your question about the VU meter lights. You stated that your meter lights do not work. It could be as simiple as your bulb burnt out. After all, it doesn't typically light up until you press the button and when's the last time you did that? But you are correct, if your bulb is good and does not light up, it could be a whole different problem. If you want to know for sure, then just check the bulb. You can certainly do that and report back to us so we have more information and provide you a more informed recommendation. We can only go with what you provided and bulbs is not something we assume is good or bad since it is a common failure part that isn't critical to operation and therefore, most folks don't even know if their bulbs are good or not. If you can change that transistor, you certainly know how to check that bulb for continuity. BTW, that transistor is probably not critical insofar as what to put in there except that it should be rated at the same current capacity or higher than the one in there. Also, pinout assignments might differ if you use a substitute so don't presume they are the same and check datasheets of both devices before installing.

Now in keeping with past such helps, please do post updates and results of the experience so that others following along can reference this in the future. Thanks.

Look, you are asking for help and let's be clear, it takes a lot of my/our time to do the homework for you and study the diagram to come up with recommendations and of potential issues based on the symptoms you provide. Let's not waste any of it by speculating on what to do AFTER a recommendation has not yet even been applied.

As for troubleshooting procedures, there is simply no way for us to provide you with a course in circuit diagnostics dynamics 101 in the short course of this thread/forum. You asked for help so please trust the judgement based on the information you've provided us and go from there. If at any time you disagree, you are free to try anything that makes more sense to you since it is, after all, your boombox. But for the moment, just please let's not get ahead of ourselves and suggest we troubleshoot further when we don't even know if that's warranted or needed. It takes time for that, so let's not waste it.

Normally, I would not even recommend replacing that transistor without first doing standard testing. This includes doing VR measurements and compare to the specs in the schematics. Armed with a set of VR measurements, it will go a long way towards finding the source of your problems. You apparently do have the schematic so if you want to know how to troubleshoot, then that is the way. That may seem like it would take an enormous amount of time, and it most definitely would if you don't narrow down the potential problem areas. This is where experience comes in and symptom analysis used to rule out areas that are probably good. In any event, if you want to be sure whether Q110 is good, and how you "should" be starting the diagnosis in this repair, then you would:

#1, check for proper voltage at the power switch.
#2, check for proper voltage at pin#1 of connector CNS/P 801
#3, check pin#1 of CNS/P 1 for voltage, approx 12.
#4, check live volts of B/E/C of Q110.

That's just for starters. Because each check above branches off to a different diagnostic path depending on the results of your test, it could soon get very complicated. So therefore, let's just keep it simple for now.

As to your question about the VU meter lights. You stated that your meter lights do not work. It could be as simiple as your bulb burnt out. After all, it doesn't typically light up until you press the button and when's the last time you did that? But you are correct, if your bulb is good and does not light up, it could be a whole different problem. If you want to know for sure, then just check the bulb. You can certainly do that and report back to us so we have more information and provide you a more informed recommendation. We can only go with what you provided and bulbs is not something we assume is good or bad since it is a common failure part that isn't critical to operation and therefore, most folks don't even know if their bulbs are good or not. If you can change that transistor, you certainly know how to check that bulb for continuity. BTW, that transistor is probably not critical insofar as what to put in there except that it should be rated at the same current capacity or higher than the one in there. Also, pinout assignments might differ if you use a substitute so don't presume they are the same and check datasheets of both devices before installing.

Now in keeping with past such helps, please do post updates and results of the experience so that others following along can reference this in the future. Thanks.


Norm it probably took longer for you to write this than actually test voltage 😉😆

baddboybill said:

Norm it probably took longer for you to write this than actually test voltage

Click to expand...

Exactly right Bill, which is why as you know, I lose my patience and get frustrated, and very soon, you and others are most likely going to be taking over my job because I'm about to turn in and retire. :hoveround: :grim:

Superduper said:

Exactly right Bill, which is why as you know, I lose my patience and get frustrated, and very soon, you and others are most likely going to be taking over my job because I'm about to turn in and retire. :hoveround: :grim:

Click to expand...

Norm, Please don't retire from here!
The attention to detail, fault detection, wise recommendations, suggestions and all kinds of help you provide on this forum is a LOT!

Tatto, here is a good link for basic troubleshooting. It has a lot of good information you might not know about.

http://conradhoffman.com/troubleshoottut.htm