Hi, got an Ibanez tone blaster tb15 with the following issue:
When powered on, it works as expected for about a minute or just a little more. Then the amplifying level is dropping in a few second to total quiet.
Now if I'll power it off an on again, it'll sound strong hum sound for less then a second then quiet, and repeat that continuously.
Powering it off for a few minutes, and I'm back to the beginning where it plays for about a moment.
Thought it's the main capacitors, one of them had an issue so replaced both.
Any idea how to fix it?
Thanks !
When powered on, it works as expected for about a minute or just a little more. Then the amplifying level is dropping in a few second to total quiet.
Now if I'll power it off an on again, it'll sound strong hum sound for less then a second then quiet, and repeat that continuously.
Powering it off for a few minutes, and I'm back to the beginning where it plays for about a moment.
Thought it's the main capacitors, one of them had an issue so replaced both.
Any idea how to fix it?
Thanks !
I would just start with a mechanical inspection checking all wire and jack connections first. Per Marcel's suggestion, even something simple like cracked solder joints or pulled PCB traces at a PCB mounted input jack could cause those symptoms. A giveaway would be to to touch the power opamp chip to see if it is overheating from oscillation.
It's more for learning with the kid, got two amplifiers, each with it's own reason not to play 🙂
Cleaned the PCB, re-iron it, and it seams to work for a minute or two after a few minutes the power is off. I'll check all the capacitors and will try to freeze the components, maybe will identify one that is getting to hot.
Try running the amp with a series bulb in the main input. A filament lamp of 1 to 2 times the power drain of the set. When powering on the amp, bulb will flash few seconds and then stay cool. Now, with this setup try to smell inside the thing searching for some straneous component running inusually hot: a capacitor, a diode, a transistor, etc.
Try also to touch any component softly with an isolating material (a piece of thin wood, plastic like icecream stick) seeking for a moovable component that when gets some temperature, makes no contact with other parts. Run the amplifier with low volume, some music programm and the LIGHT BULB.
Try also to touch any component softly with an isolating material (a piece of thin wood, plastic like icecream stick) seeking for a moovable component that when gets some temperature, makes no contact with other parts. Run the amplifier with low volume, some music programm and the LIGHT BULB.
It is sad, but often impossible to find a schematic for cheap amps like this. As if the manufacturer does not want you to try anf repair it..
I would look at the power amp IC. Does it get hot? maybe something fell into the amp and causes a short between two legs of the chip?
If a metallic piece dropped inside, and in a site that can cause a shortcircuit, the amp will no further run any way. If in signal or low power location, it definitively cause the amp to be mute. And if is in a power sector, an intersting shortcircuit surely caused destruction or collapse at entire circuit. And not timered or temperature dependent problem.
Obvious, my own experience and not necesarily true all cases.
Obvious, my own experience and not necesarily true all cases.
Ok, a noble goal.
That said, the proper way to learn is first to learn, meaning Electronics theory, build some simple stuff, measure, test, etc. , I'm talking "known" circuits, where you have schematics, datasheets, can get parts, etc., and when you have the background/experience, been through a dozen or two amps successfully, then you try your hand at a "mystery" one, no schematic, no data, etc.
Going the opposite way is frustrating.
Given your amp and symptoms, for reliable servicing, which starts with diagnosing the problem, you need s signal generator (easy) and a scope, to see exactly what is happening and where.
No need for a fancy expensive scope, even I bought one of these cheap multimeter sized ones to carry in my service bag, go figure.
https://www.epanorama.net/newepa/2018/12/16/dso150-pocket-oscilloscope/
It is perfectly fine for your amp, it can display up to 50V DC/peak.
Anything else is shotgunning or trying to hit the piñata blindfolded
Oh, they are available from multiple sources for 20 something bucks, add 8$ for cheapest China shipping.
Will take about 1 Month, no big deal
As a side note, you did not help us much, didn't even show a couple gut pictures.
What kind of answers do you expect?
Hi,
I think this is the parts list for your amp and hope it might help you:
https://www.manualslib.com/manual/522358/Ibanez-Tb15.html
If you would like to get the most from the learning opportunity, here's a suggestion. When I first started learning about electronics I fixed a similarly simple Epiphone EP800 for a friend, and got lucky poking around without a schematic (or much knowledge!)
But then I thought it would be a great place to start learning how to develop a schematic from an existing circuit board and actually understand what was going on. With a simple circuit like this it's a fun puzzle. Start by identifying the different functional circuits and draw them the best you can based on the solder traces. If you take a good photo of both sides of the board I think you would find it easy to get helpful feedback here for any mistakes you make.
If you're more interested in fixing the amp than learning what makes it work, you will get there eventually by swapping components and looking for bad traces/solder joints if you're patient.
I think this is the parts list for your amp and hope it might help you:
https://www.manualslib.com/manual/522358/Ibanez-Tb15.html
If you would like to get the most from the learning opportunity, here's a suggestion. When I first started learning about electronics I fixed a similarly simple Epiphone EP800 for a friend, and got lucky poking around without a schematic (or much knowledge!)
But then I thought it would be a great place to start learning how to develop a schematic from an existing circuit board and actually understand what was going on. With a simple circuit like this it's a fun puzzle. Start by identifying the different functional circuits and draw them the best you can based on the solder traces. If you take a good photo of both sides of the board I think you would find it easy to get helpful feedback here for any mistakes you make.
If you're more interested in fixing the amp than learning what makes it work, you will get there eventually by swapping components and looking for bad traces/solder joints if you're patient.
Thanks, very useful.👍🏻
It is maddening that the parts list is available but not the schematic but hey ... worse is nothing.
At least we know it has 1 or 2 RC4558 in the preamp and is powered by an LM1875
That suggests points to scope.
Inject 100mV 400Hz or 1 kHz at input, set all knobs on "5", scope pins 1 and 7 (outputs) on all Op Amps, pins 1 (input) and 4 (output) at LM1875.
You must have signal on all of them at turn on which will disappear or get very distorted after 1 or 2 minutes.
That will lead you to the failure.
This is the troubleshooting/fault finding procedure; anything else is random guessing.
Can you guess right?
Yes, you can also guess the jackpot number right.
About same probability. 😫
It is maddening that the parts list is available but not the schematic but hey ... worse is nothing.
At least we know it has 1 or 2 RC4558 in the preamp and is powered by an LM1875
That suggests points to scope.
Inject 100mV 400Hz or 1 kHz at input, set all knobs on "5", scope pins 1 and 7 (outputs) on all Op Amps, pins 1 (input) and 4 (output) at LM1875.
You must have signal on all of them at turn on which will disappear or get very distorted after 1 or 2 minutes.
That will lead you to the failure.
This is the troubleshooting/fault finding procedure; anything else is random guessing.
Can you guess right?
Yes, you can also guess the jackpot number right.
About same probability. 😫
If the amp does have an LM1875, see if it gets too hot to touch. If so, change it. Odds are it's the problem.
Powered the amp from my phone to let it run with some low volume music into the CD input. It will play it just fine even after the guitar input is getting it's issue. I ordered the amplifier and the 4558DD with sockets, just in case.
Touched gently all parts after about 5 minutes it plays, nothing's getting too hot. Trying to move the different components, didn't have any impact on the output sound. As I already assembled everything back, will upload images once the ordered components will arrive and I'll open the box again.
As for test equipment and knowledge, I guess I have a little of both. An old signal generator, a CRT fully functional scope, and a Fluke meter.
Will follow the different suggestions in the thread and update with any insight.
Thanks all for your comment.
Touched gently all parts after about 5 minutes it plays, nothing's getting too hot. Trying to move the different components, didn't have any impact on the output sound. As I already assembled everything back, will upload images once the ordered components will arrive and I'll open the box again.
As for test equipment and knowledge, I guess I have a little of both. An old signal generator, a CRT fully functional scope, and a Fluke meter.
Will follow the different suggestions in the thread and update with any insight.
Thanks all for your comment.
seeing as how the CD input works but the guitar input dies it's not likely the output, i'd say it was a cap in the preamp.
Way to go.
Try to find where signal gets lost.
Which, as suggested above, might even be something "mechanical" such as a jack, pot or connector
Avoid replacing ICs at random "just to see if you solve the problem", it does not work that way.