Telefunken CR 100 distortion only with batteries

[dubout]

I have a Telefunken CR100 boombox. It sounds fine when operating with cable / AC but the bass is distorted already at a very low volume when operating on batteries / DC. Does any one know where to look to sort this out?

Also there is no fm reception, only static. Could both errors come from the same problem?

 

[JVC Floyd]

Sounds to me like you're not getting enough battery power I would check the charge of the batteries and the condition of the springs in the battery compartment also clean any AC/DC switch you might have anything that will impede the flow of current from the battery compartment to the amplifier ,amplifiers do distort when starved of power also the tuner gets weak and won't pick up anything but static.

 

[dubout]

If I think about it you are right. It's the same effect when the batteries die out. Why didn't that come to my mind?! The suggested procedures however were already made with no effect. After your post I tried again with cable and the effect is the same but it appears at a much higher volume. To be precise for others with a similar problem, the tuner doesn't pick up any stations when running on AC either.

This indicates that there is something wrong on the board, presumably a dying capacitor. I have ordered replacement for the three largest caps and will change them first. As I don't have a service manual (anybody? ) I have to go by trial and error and report how it goes.

 

[dubout]

I have exchanged the three large caps but no success. A friend told me to try and exchange the diodes next. Does anybody know a source where to find these two? S3VC doesn't bring too many useful results on google.

 

[HE3R0]

I have exchanged the three large caps but no success. A friend told me to try and exchange the diodes next. Does anybody know a source where to find these two? S3VC doesn't bring too many useful results on google.

In case you will not be able to find replacement diodes (i was not able to find them), you can make your own rectifier bridge.

 

[dubout]

In case you will not be able to find replacement diodes (i was not able to find them), you can make your own rectifier bridge.

I have no clue what I have to do but I am willing to learn, will dig into that and report. Much appreciated, thank you!

 

[kudlaty_dm]

Instead of changing diodes (which probably will not fix the issue) take a look at those 4 capacitors with 0,02uF. They are around the diodes. There is a possibility that they are shorted, that's why you have disorted sound at low ranges.

 

[dubout]

Instead of changing diodes (which probably will not fix the issue) take a look at those 4 capacitors with 0,02uF. They are around the diodes. There is a possibility that they are shorted, that's why you have disorted sound at low ranges.

Yeah, I figured that it might not be the diodes and was pointed to transistor T301. Very hard to find as it is screwed to a cooling element! I saw that around this transistor there is black smut on the resistor beside it and on the board. So my guess now is that the transistor leaked and I ordered replacement for it. Waiting for parts ... again. =)

The whole unit was covered in white fluff like it was standing near a cloths dryer for years. Maybe that trapped the heat inside it and the transistor overheated?!

Your suggestion is still helpful as I will change those caps if I have the right replacement caps at hand just in case.

 

[dubout]

Just to give an update, I exchanged the four ceramic caps around the diodes with no effect. I also replaced the transistor T301 and some random caps which I had available, also with no effect.

The light for the dial won't light up but the bulb is intact. Also the current from the transistors on that board seem to be slightly off. For example if the manual gives the current for B with 0,75 V and I measure 0,69 V, that's an error, right?!

However, this makes me think the error must be around there, on the small board with the volume adjust. I can only poke around in the dark as I am such a noob ... But I am learning, not least because of the help here! I will exchange all electrolytic caps on said small board and see what happens.

 

[dubout]

I exchanged more caps and found a short in the flat cable. The distortion seems to be gone on one side, the other speaker still distorts. So close ...!

There are two 3 pin rectifiers I would like to replace but I cant find replacements (brown and black, see picture above). I don't know how to build my own rectifier so I am putting this unit away. Maybe I can use it as a spares unit or I will eventually throw it away. Thanks for the help everybody!