VU meter not working. Dynacord Echocord Super 76

[JimB]

The old one must be desoldered first?

Yes

Could I place it from the bottom side insted of taking everything apart.

Yes

JimB

 

[Rorut]

Any easy way to get that old one out from this side? Dont want to damage any copper path

 

[Rorut]

What would do as a replacement?

 

[alec_t]

A BC547 is rated for 45V so should do as a replacement.
Snipping the legs of the old T200 might be easier than de-soldering and would not risk copper track damage.

 

[alec_t]

R206 is only 50K measured. Should be 68K.

R206 has R202, 207, 209 in parallel with it, so 50k is a reasonable measurement.

 

[Rorut]

There is a BC547B and a BC547C
Whats the difference between ”B” and ”C”.
I think I have a ”B” somewhere.

 

[Les Jones]

The suffix letter specifies the range of hfe values. If you are using the data sheet from Philips the information is on page 3.

Les.

 

[Rorut]

Thanks. Would the BC547B that have some difference in Hfe max work for me?

BC237B
Hfe min = 200
Hfe typical = 290
Hfe max = 460

BC547B
Hfe min = 200
Hfe max = 450

 

[Les Jones]

The BC547B should work.

Edit. Don't forget that if you solder the transistor to the etch side of the board that the position of the emitter and collector pads will be the mirror image of when viewed from the component side.

Les.

 

[alec_t]

In this circuit the hfe is not critical.

 

[Rorut]

Ok have it apart now and desoldered transistor. Seem like it is a different model than whats in the schematic. BC107B

Can I still replace it with my BC547B?

 

[Les Jones]

Compare the information in the datasheets for both devices. If you trace the schematic of that area of the board and it matches the schematic thet you posted then almost any small signal silicon NPN transistor should work. You should be able to find the data sheets using Google or any other search engine.

Les.

 

[JimB]

Can I still replace it with my BC547B?

Yes.

JimB

 

[Rorut]

I found a 107 and replaced the old one. Now the VU meter works perfectly. Thanks a lot all of you!

 

[JimB]

A success story - I love it!

JimB

 

[alec_t]

Good to hear.

 

[schmitt trigger]

Good for you!

Earlier type of transistors sometimes suffered from bonding wire unreliability, as others have mentioned. With the actual current and voltage levels it is unlikely that an electrical over stress damaged it.

 

[Rorut]

Yes really appreciate it. Thanks!
Another question related to the machine. Im not sure if this is in my imagination but using it for a couple of hours it feels like sound gets a bit distorted. I have not change the tape loop and don’t know the age of that. Any ideas on this? Can old caps affect sound quality?

 

[alec_t]

Certainly old caps can affect sound quality, if they are in some frequency-sensitive part of the circuit. Their values and ESR can change with age. Electrolytics are the type most prone to cause problems as they age.

 

[Rorut]

Certainly old caps can affect sound quality, if they are in some frequency-sensitive part of the circuit. Their values and ESR can change with age. Electrolytics are the type most prone to cause problems as they age.

Some people say let it be if it works, other places I read replace all electrolytic caps. Would like to put in high quality caps if I do it . What do you think?