Panasonic AN7220A IC. - UK Vintage Radio Repair and Restoration Discussion Forum

pantherslover · 14th Nov 2018, 1:30 pm

Hello everyone.

I only have basic understanding of solid state electronics. I'm actually a robotics repair engineer formerly.

This concerns a Panasonic GX500 4 band TL radio receiver.

Some time ago I lost reception on LW which is my lifeline to the 198kHz Droitwich transmitter.

It's as if the ferrite rod coils have been disconnected. Also when I press the ferrite rod the MW reception clicks on and off.

Anyway don't let that distract you.

The set uses an AN7220 radio chip. Below is a very technical description of is function.

'http://pdf.datasheetcatalog.com/datasheet/panasonic/AN7220.pdf

Now when fiddling around in bed with the multimeter last night if I put a test probe on either pin 2 AM mix output or 17 oscillator coil I can get some reception. Both 2 and 17 are in close proximity on the chip and also both are connected to coils.

Can perhaps someone suggest how I fix this?

Thank you.

See_Mos · 14th Nov 2018, 6:18 pm

Sounds as if it is going unstable. The data sheet shows a 10uF electrolytic across the supply pins 3 and 16. Find it and replace it then try again

Marconi_MPT4 · 14th Nov 2018, 8:26 pm

Hi and welcome to the forum.

References to GX500 suggest it might have been also marketed as RF3500, in any case this model contains the AN7220A IC and has four wavebands.. might be a coincidence.

As a first step, when the fault occurs do you see a change of voltage on pin 1 or pin 17? Should be about 3V with respect to battery negative. Now when you switch between bands does the voltage disappear? This DC voltage will indicate if the L, M, S wave circuits, switch and coils have continuity.

Rich

Maarten · 14th Nov 2018, 8:32 pm

First, check the soldering and traces around the ferrite antenna. At the very least you will probably find a loose connection that will affect the MW reception, but maybe you can solve both problems at once.

pantherslover · 15th Nov 2018, 2:23 pm

On 17 I get 3V on LW, MW and SW 0.5V on FM and dropping

On 1 I get 3V from SW and nothing else.

I checked the antenna coils first, I can't see any problem.

It's only 2 years old.

14th Nov 2018, 1:30 pm	#1
pantherslover Retired Dormant Member Join Date: Nov 2018 Location: Orgiva, Granada, Spain Posts: 2	Panasonic AN7220A IC. Hello everyone. I only have basic understanding of solid state electronics. I'm actually a robotics repair engineer formerly. This concerns a Panasonic GX500 4 band TL radio receiver. Some time ago I lost reception on LW which is my lifeline to the 198kHz Droitwich transmitter. It's as if the ferrite rod coils have been disconnected. Also when I press the ferrite rod the MW reception clicks on and off. Anyway don't let that distract you. The set uses an AN7220 radio chip. Below is a very technical description of is function. 'http://pdf.datasheetcatalog.com/datasheet/panasonic/AN7220.pdf Now when fiddling around in bed with the multimeter last night if I put a test probe on either pin 2 AM mix output or 17 oscillator coil I can get some reception. Both 2 and 17 are in close proximity on the chip and also both are connected to coils. Can perhaps someone suggest how I fix this? Thank you.

14th Nov 2018, 6:18 pm	#2
See_Mos Hexode Join Date: Nov 2003 Location: Ossett, West Yorkshire, UK. Posts: 482	Re: Panasonic AN7220A IC. Sounds as if it is going unstable. The data sheet shows a 10uF electrolytic across the supply pins 3 and 16. Find it and replace it then try again

14th Nov 2018, 8:26 pm	#3
Marconi_MPT4 Heptode Join Date: Mar 2011 Location: Dorset, UK. Posts: 521	Re: Panasonic AN7220A IC. Hi and welcome to the forum. References to GX500 suggest it might have been also marketed as RF3500, in any case this model contains the AN7220A IC and has four wavebands.. might be a coincidence. As a first step, when the fault occurs do you see a change of voltage on pin 1 or pin 17? Should be about 3V with respect to battery negative. Now when you switch between bands does the voltage disappear? This DC voltage will indicate if the L, M, S wave circuits, switch and coils have continuity. Rich __________________ To an optimist a glass is half full; a pessimist half empty; an engineer twice as big as need be!

14th Nov 2018, 8:32 pm	#4
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,199	Re: Panasonic AN7220A IC. First, check the soldering and traces around the ferrite antenna. At the very least you will probably find a loose connection that will affect the MW reception, but maybe you can solve both problems at once.

15th Nov 2018, 2:23 pm	#5
pantherslover Retired Dormant Member Join Date: Nov 2018 Location: Orgiva, Granada, Spain Posts: 2	Re: Panasonic AN7220A IC. On 17 I get 3V on LW, MW and SW 0.5V on FM and dropping On 1 I get 3V from SW and nothing else. I checked the antenna coils first, I can't see any problem. It's only 2 years old.