Long Shot.... Bombeat RT-F483

[mu1sic2ian3]

Hi all, I picked up this Toshiba RT-F483 because I have a thing for mono boomboxes as well as mono boomboxes where the cassette is right side up. I want to preface all this by saying I am a complete novice to this hobby. I know how to solder and I own a multimeter but that's about it. I have replaced belts and cleaned tape heads ect but I would have no idea where to start to try and diagnose the problem with this box.

Anyway, The issue is it has power but no sound output whatsoever. The radio seems to work (you can see the tuning light change when you find a good station) and you can hear the cassette motor run when you press play even though the belts are toast but there is no sound from either the speaker or from the headphone output.

As a side note, I'm in the USA and as far as I can tell this might be a European model as the power input is actually 220v. It looks like the person who had it before me was trying to power it off of 110v and I wonder if that could have damaged the circuitry. So I'm powering it off of batteries for now. I cant find a service manual or a schematic (not that I would know how to read it) in fact there isn't much info on this box at all that I can find. Just this one page...
https://www.radiomuseum.org/r/toshiba_radio_cassette_recorder_rt_f483.html

I've looked at the circuit board and can't see a single cracked solder joint, I don't see any obvious leaking capacitors or anything but then again I don't really know what I'm looking for. I have a feeling repairing this thing may be above my pay grade, but I thought I'd at least give it a try...

Just wondering if there are any obvious things I can try before throwing in the towel on this bad boy...

Thanks

 

[Tinman]

Hello.
Have you tried working all of the switches, buttons and knobs/pots back and forth (numerous times) to see if anything changes?
If not, you might want to try that along with working the record bar which is labeled rec/pb.
Preferably you want to use some kind of cleaner (electronics) when working everything.
This is probably the easiest thing to try since you already have it apart.

 

[mu1sic2ian3]

Hello.
Have you tried working all of the switches, buttons and knobs/pots back and forth (numerous times) to see if anything changes?
If not, you might want to try that along with working the record bar which is labeled rec/pb.
Preferably you want to use some kind of cleaner (electronics) when working everything.
This is probably the easiest thing to try since you already have it apart.

Hi, thanks for the reply I guess I should have mentioned that I do also have contact cleaner. I did spray the pots and worked them back and forth to no avail. I didn't think about the switches since they seem to be working. But I can try that. I just noticed the Record Bar, but would that effect the radio as well or just the cassette portion?

 

[AE_Stereo]

Having a Mono with Right Side Up is very very rare.
But I thought, having that with Autoreverse too is impossible.

You have got a fantastic find.

Yes, that record bar affects everything that goes to the speaker amp.

 

[mu1sic2ian3]

Yeah I thought the auto reverse was unique as well. Of course if I can get it going I still have to replace the belts (which look a little complicated) and hope everything works with the mechanism... It's got one of those heads that spins, I tend to stay away from auto reverse because I feel like it's more stuff to go wrong but this one I couldn't resist. That's actually great news about the record bar, at least it's something else I can try... Thanks!

 

[mu1sic2ian3]

No joy unfortunately, the record bar was free moving, I sprayed it with a bunch of contact cleaner anyway and it didn't seem to make a difference no matter what position the switch was in...

 

[floyd]

If it has any kind of external Inputs I would try those otherwise my guess would be a bad amplifier ic chip.

 

[mu1sic2ian3]

If it has any kind of external Inputs I would try those otherwise my guess would be a bad amplifier ic chip.

Yeah thanks, I just took the heat sink off the main chip and it appears to be one a TA7225P chip. There are a few for sale online, wondering if its worth spending the $30 or so dollars to try that.

 

[Tinman]

It's tough when you don't have a service manual available.
If you're bored, another long shot would be to check the resistors.
It's not very fun but since it's a pretty small board it shouldn't be too difficult.
If you do it, test them with the power off and after reading one, mark it with a sharpie so you know it's good.
If you want to know the value of a resistor, you can google "resistor calculator" and input the color bands.

 

[caution]

If you're getting absolutely no audio at all, not even a pop or crackle, from the speaker or the headphone jack, and you are able to read a healthy voltage on pin 2 and pin 8 (positive and negative rails) of the amp chip, then yeah the amp is probably toasted.

 

[floyd]

Hi all, I picked up this Toshiba RT-F483 because I have a thing for mono boomboxes as well as mono boomboxes where the cassette is right side up. I want to preface all this by saying I am a complete novice to this hobby. I know how to solder and I own a multimeter but that's about it. I have replaced belts and cleaned tape heads ect but I would have no idea where to start to try and diagnose the problem with this box.

Anyway, The issue is it has power but no sound output whatsoever. The radio seems to work (you can see the tuning light change when you find a good station) and you can hear the cassette motor run when you press play even though the belts are toast but there is no sound from either the speaker or from the headphone output.

As a side note, I'm in the USA and as far as I can tell this might be a European model as the power input is actually 220v. It looks like the person who had it before me was trying to power it off of 110v and I wonder if that could have damaged the circuitry. So I'm powering it off of batteries for now. I cant find a service manual or a schematic (not that I would know how to read it) in fact there isn't much info on this box at all that I can find. Just this one page...
https://www.radiomuseum.org/r/toshiba_radio_cassette_recorder_rt_f483.html

I've looked at the circuit board and can't see a single cracked solder joint, I don't see any obvious leaking capacitors or anything but then again I don't really know what I'm looking for. I have a feeling repairing this thing may be above my pay grade, but I thought I'd at least give it a try...

Just wondering if there are any obvious things I can try before throwing in the towel on this bad boy...

Thanks

That big gray capacitor next to the amplifier heat sink looks like it might be bulging a bit so I would check that as well.

 

[mu1sic2ian3]

Ok, thanks all for the advice. I'll definitely try your suggestions and see what I can do before I throw in the towel.

This has been very helpful!

 

[mu1sic2ian3]

HI all, just a small update. The amp chip does at least have power. I'm getting around 9v between pins 2 and 8. Also I found the board schematic. Doesn't do me much good because I cant read it but I figure I'd post it here in case it gives any ideas on the next best place to start...

Thanks.

 

[caution]

Actually you shouldn't see any difference between pins 2 and 8, I can see on the schematic that they are tied together on this model. When you measured with your meter, did you touch one probe to ground somewhere and the other probe to the amp pins?

It could be that the chip is dead, since it's getting power.

 

[mu1sic2ian3]

Actually you shouldn't see any difference between pins 2 and 8, I can see on the schematic that they are tied together on this model. When you measured with your meter, did you touch one probe to ground somewhere and the other probe to the amp pins?

It could be that the chip is dead, since it's getting power.

No I touched one probe to 2 and one to 8.

 

[caution]

Everything you measure needs one probe tied to ground.
My money is on the amp, but maybe you can check the rest of the voltages listed around the amp chip on the schematic to confirm.

 

[Superduper]

Keep in mind that the audio traverses the earphone jack. If the jack has a connectivity issue, even if the amplifier was outputting the proper signal, the speaker may not get that signal. This is not an uncommon issue. Sometimes, if a plug has been inserted into the jack for a long time, the spring connection loses it's tension and you lose audio at the speaker. You can check by inserting a headphone into the jack. If you get audio in the headphones, you've found the issue.

 

[Spax]

Looking at the schematic the headphone jack will cut out the signal to the speaker, I solved a no sound issue on one of my boxes by inserting a headphone jack a few times whilst trouble shooting. When I get round to restoring I'll be hitting it with deoxit and a cotton wool bud (Qtip).

Edit: Superduper got there before me

 

[mu1sic2ian3]

Looking at the schematic the headphone jack will cut out the signal to the speaker, I solved a no sound issue on one of my boxes by inserting a headphone jack a few times whilst trouble shooting. When I get round to restoring I'll be hitting it with deoxit and a cotton wool bud (Qtip).

Edit: Superduper got there before me

Yeah plugged headphones into the jack and there's not even a hint of a signal. I don't think the audio is making it to the headphone jack.

 

[Superduper]

Bummer. That would've been the easiest fix. However, the result does not for sure absolve the headphone jack. There is an internal tang that could break off in which case, neither the speakers or headphones would work. The only way to know for sure is to test the headphone jack for a signal with a signal tracer. Or... if you can follow your way around a schematic, check for continuity from the speaker (+) to along the path towards the amp chip to ensure that there are no breaks. Typically, if you are going to attempt audio electronics repair, you'd need more tools than just a soldering iron and a cheap multimeter. A signal tracer would be immensely helpful to trace along the path. Audio can be heard across the entire path, even across capacitors and resistors. If you probe along the path and it's dead from the speaker until you've reached a component (along the path), and you find audio on one side but not the other, you've probably located the source of the failure. Another tool would be an audio signal generator/injector. Injecting the signal along the path should cause audio to be heard from the speakers. You would attenuate the signal as you work towards (and past) the amplifier. The same principle applies. The process with only a multimeter is a little more limited. I would work with the schematic and check to make sure have continuity all along the audio path. Print it out and use a highlighter to mark all areas that you tested for continuity. If there are appurtenant resistors, check and ensure that they within specs. If they are reading high, they are bad. If they are reading low, more testing needs to performed. Also, the schematic shows voltage specs for the amp chip pins. Check them all, and compare to what the specs are. Some small variations are not uncommon but anything significant can suggest circuit issues. If you don't know how to interpret the results, you can post them here.

Although an amplifier chip failure is not uncommon, it is far less likely than other issues on small mono low powered devices like these that don't have external speaker connections. External speaker connections allow the user to introduce errors such as speakers with ultra low impedance, or accidentally short speaker wires, even momentarily. On the other hand, if the internal jack tang broke off, it is possible it could bridge and short the audio signal to ground causing the amp to blow.

At this point, you could try to just start swapping parts. Or you can perform the VR tests suggested above in the first paragraph. Or you can invest in more tools and perhaps do some diy learning. Or you might want to just unload this unit to someone more capable and use the proceeds to purchase another fully working one. The difference in price could simply be considered the cost "repairing" it.