Beomaster 6500 tuner issue

3 replies
J(
Offline
judgefilip (archived2)
Bronze
Posted October 31, 2014 at 21:35 GMT
#2201455

Hello everyone,

My BM6500 has developed an issue with its tuner. A while ago I replaced old caps in audio signal path, power supply, CPU board and front PCB (to improve two-way ir communication). Unit works really well, I was astonished by its sound quality to be honest... Remote range has improved greatly. The only problem that has developed since recapping the BM is a strange issue with its tuner.

When recalling memorised stations by pressing a number on a remote directly everything works fine, but using 'step < >' buttons, or 'program step' button on the front panel causes some king of audible discharge. Then the station tunes correctly and everything works ok.

I haven't been using it a lot since i thought it has been misaligned or something, because it required really strong signal and even when using external powered antenna the reception was bad. Opposed to my BM7000 which easily locks on correct frequency just with simple 0,5 m of wire attached as antenna. A friend of mine told me not to touch anything on the tuner board, as replacing electrolytic caps may totally misalign the tuner. I decided not to listen to him and replaced all caps on the tuner board, also, I desoldered a wire connecting the tuner board with the antenna socket.

Sound quality has improved A LOT, as FM reception did. Now BM6500 locks to a frequency (with stereo) just as easily as my BM7000, but the strange issue with irritating discharge remains...

Could anybody possibly tell me how to fix this, please?

I recorded a video showing mentioned issue. In the beginning I recall memorised station directly with numbers, later on, I use Step < > buttons.

[View:http://www.youtube.com/watch?v=Bs79wrTPmrE:800:0]

Thanks in advance!

Filip

DI
Offline
Die_Bogener
Bronze
Posted November 5, 2014 at 15:20 GMT
#2201456

It could be a crack in the connectors of the cpu board. It looks like the "mute" command/signal is missing and the the Sound is not switched off... then you can hear distortions during the small time the tuner changes the frequency.

Very often there are cracks in the solder of the cpu board where the black cables are connected.

The same happens sometimes to the same connectors of the tuner board, the pins break out of the board. 

J(
Offline
judgefilip (archived2)
Bronze
Posted November 19, 2014 at 14:54 GMT
#2201457

Thanks for your response Die_Bogener!

Desoldering all connection sockets both on CPU board, tuner pcb and preamplifier boards didn't help, but I've found the problem! It was caused by bad C66 cap. Although I've replaced it recently using only HQ components, it measured way out of specs. After replacing it the problem is solved.

But...

A week ago I was listening to some CDs and was on my way out, so I used the standby switch in front of Beomaster to turn off the system. Suddenly I've heard a series of strange relay clicks, then 3 seconds of buzzing from inside of the BM and the standby light went off... I've found out that main fuse, before power transformer is burned. After replacing it with 2A one. System returned to standby. Right speaker worked correctly, but the left one was silent... After some time I've found burned trace on the amplifier section, near the power output transistor IC1. After resoldering it the system works as it should, apart from the FM tuner which is now dead :( AM section works as it should, but when switching to FM all I hear is static. Recalling memorised stations works, the frequency is displayed correctly on the MCP6500, but still all I hear is static. I guess there must have been some kind of power surge caused by malfunctioning relay on the power supply board. After replacing the tuner board with one from BM7000 the radio works correctly, again no problem with the lack of muting when changing stations. At least one problem is solved, but now I have a damaged FM section of the tuner.

Does anybody know where should I start diagnosing the board? I've already checked most resistors and diodes and they are ok. TP16 on the tuner board shows a range of voltage when tuning stations. 1-28V as I remember correctly. To be honest now I have two broken tuner boards from two different BM6500s. On was after a power surge failure and the tuner is behaving exactly the same. I suspect damaged ICs. Possibly the SP8629 prescaler chip.

Could anyone help me to solve this riddle?

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