Sony CFD-5 does not turn on

[Jozsef1981]

Hello Everyone,

First of all sorry for my english. But I'm on that to improve.

I just picked up a Sony CFD-5 boombox from a garage sale. It is in really good cosmetic condition, but I was not able to power on at all. Did nothing on every sources. No LED lights. Looks dead from outside. Unfortunately I have no batteries or 12V DC power supply to test these type of methods.
All fuses and cable connections have checked. No issue found.
I wanted to measure DC values of the internal power source. There is only a cable harness with 4 wires which feeds the main board.

Measures with connected main board
Orange 0V
Red 17.55V
Black 0V
Yellow 17.53V

Measures with disconnected main board
Orange 0V
Red 18.3V
Black 0V
Yellow 18.28V

As I see in service manual 15.7V DC has to be as main DC voltage if I feed unit from 230V AC.
Everything looks original inside. Nobody did any hack before. I really don't understand why my DC voltage higher directly out from internal power source.

Anybody familiar with this type?

Here you can find the service manual:

cfd_5_service_manual_en : Sony : Free Download, Borrow, and Streaming : Internet Archive

1985 Sony CFD-5 Boombox Service Manual - English

archive.org

Thanks for your check and help!

Cheers from Hungary,
Jozsef

 

[Superduper]

It’s because the internal power supply is unregulated so the actual power supply output will vary based on the load. This is normal. The internal circuitry voltage specs are based on a stable voltage input which can be supplied via an adjustable bench power supply. However I suspect most technicians will simply adjust their findings during voltage checks to account for a higher input voltage.