FM problem on Braun radio

11/12/2009 9:36:05 PMRon

When it is working , it sounds great

Problems:

1. FM stations drifts
2. FM will turn motorboating every once in a while or when 1st power up , can usually be fixed by switching back & forth with AM
3. AM doesn't ave motorboating nor drift problem.

I thought about cleaning the matrix for band select, but there is no easy access without taking the whole thing apart. it is embedded between the chasis & a board for most of the tuning ckt.

I assume drift and motorboating are 2 seperate problems. Any suggestions ?

Thanks.

if schematic doesn't show up , please use below link:
http://picasaweb.google.com/lh/photo/9xq5nqmvyesDU2QhmG-Qbg?authkey=Gv1sRgCLO7ivzvvMCHvgE&feat=directlink

11/12/2009 9:38:27 PMRon

one more try to attached schematic..
:

:
:
:When it is working , it sounds great
:
:Problems:
:
:1. FM stations drifts
:2. FM will turn motorboating every once in a while or when 1st power up , can usually be fixed by switching back & forth with AM
:3. AM doesn't ave motorboating nor drift problem.
:
:
:I thought about cleaning the matrix for band select, but there is no easy access without taking the whole thing apart. it is embedded between the chasis & a board for most of the tuning ckt.
:
:I assume drift and motorboating are 2 seperate problems. Any suggestions ?
:
:Thanks.
:
:if schematic doesn't show up , please use below link:
:http://picasaweb.google.com/lh/photo/9xq5nqmvyesDU2QhmG-Qbg?authkey=Gv1sRgCLO7ivzvvMCHvgE&feat=directlink
:

11/14/2009 6:50:12 PMBill G.

Hi Ron,
Before you go through the trouble of dismantling the radio to get at the band switch try two things. First, try switching back and forth between the bands several times (~20 times) fast. This can clean the band switch contacts.
Second, look for bad connection between tube and socket. Spraying your contact cleaner there may be helpful.

If that doesn't do it you may need to do the long dismantle.

Best Regards,

Bill Grimm

11/15/2009 4:13:22 AMRon

Hi Bill,

Thanks for the suggestions. I will give it a try. In a way, I have been kind of doing the band switching over times without even noticing it. This is a radio I just bought and the previous owner said it did nothing but motorboating in FM and all other bands didn't work. I was fully planning on at least changing the power supply caps. After I cleaned up the circuit , dust everthing off, FM was actually working on the fist powered up. AM is ok too. So I am putting the recap off. Sound is not bad but bass control has little to no effect. I will change one or 2 cap to see if it makes any difference. Any suggestion ?

Can I use tuner cleaner for contact cleaning, just spay it ? I use tuner cleaner for sticky potentiometers.

Again , once power up for a while( maybe 1/2 hr), motorboating won't happen. it continues to drift though but only once in a long while. I might just live with these issues for the time being.

:Hi Ron,
: Before you go through the trouble of dismantling the radio to get at the band switch try two things. First, try switching back and forth between the bands several times (~20 times) fast. This can clean the band switch contacts.
: Second, look for bad connection between tube and socket. Spraying your contact cleaner there may be helpful.
:
: If that doesn't do it you may need to do the long dismantle.
:
:Best Regards,
:
:Bill Grimm
:

11/15/2009 9:05:33 PMBill G.

Hi Ron,
Tuner cleaner is the same stuff. That is what to use on your band switch.
A re-cap may do the trick on getting this working reliably. I had thought you had already done it.

Best Regards,

Bill