toshiba sb-445 repair

[vicelord]

Ok so the story of this amplifier is unknow to me. I have bought this as non working for 10$ to use the transformer in another project.
When i got home with this pice of engineering i took a look inside and found a broken fuse, i replaced the fuse and the amplifier started after that i tried it on a pair of headphones and sounded fine. I then wanted to hook it up to my speakers to hear it properly but when conected to speakers the sound is very muddy and distorted.
I then looked inside there where signs of previous repairs. I disasambled the boards from the case and started resoldering components but this didint resolve the situation. After this i found one of the 0r47 is broken right in half but didnt have a spare one.
I will go to the electronics shop for that resistor but please tell me if there is something else o should buy like electrolitics.

Sorry for my bad english.

regards

ps here is the service manual TOSHIBA SB-445 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics

[bob91343]

That certainly could account for the distortion. It means that only one output transistor is passing current. Hopefully the rest of the parts are good.

[vicelord]

Well only the body of the resistor is craked the wire inside is intact


regards

later edit.
the sound is muddy on both chanels so i dont think one pair of transistor isnt working because there is only one pair for each chanel.

[robert scalpello]

Hi. Please can you help me and guide me to solve the problem? I have just bought a toshiba sb 445 from ebay. The seller said that it's in a good working condition, but as soon as I received it, I tested it and the output on the loudspeakers is very low, even though the volume is full on to its maximum and the specs stat that it is rated at 45watts per channel. I opened it but everything seems to be in order. The only thing that I noticed is that when it is being switched off, the volume seems to increase to a higher output, but then it fades away. What and where could be the fault? Thanks.

[sregor]

Find an owners manual. The schematic shows a "fader switch" which controls a muting circuit at the input of the power amp section. I'm not familiar with the circuit, but it looks like it might give you the symptoms you described. Good luck.

[jerluwoo]

You need to get yourself a multimeter and check a couple things. Replacing stuff blindly wont do you much good. My first thought is if the headphones played fine, no distortion etc. then the emitter resistors are all suspect to be open. I have seen this happen on various amplifiers a few times. The reason I would think this is because the only difference between the head and speaker outs are series resistors for the headphones. The driver transistors would be able to drive the phones by themselves but not a speaker. An easy check would be to check how hot the emitter resistors of the drivers get with a speaker hooked up. Report back with your findings.

[sakis]

99% of vintage amplifiers need re soldering and recaping ..... most important are the small capacitors related to feedback and secondary power supply

then all the others need to be checked that will mean voltage according to the schematic pots relays and switches to be cleaned ..

info can be also found here

vintage amplifier repair/upgrade manual