ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hello to b&O lover , I’ve read a lot on this site like voyeur but never write .Some week ago a friend of mine give me three B&O center .A BeoMaster 4400 , BeoMaster 901 and beocenter 2100 .I use to fix amp and old hifi most from 60&70 and help some HiFi entusiastic to play their stereo system at best I can .Restoring old HiFi is my hobby . I try to resume the beomaster 901 , this receiver is in good condiction , were some issue with slider and bias due scrapped trimmer .I cleaned and replaced the 500 ohm trimmer The 901 has the right size for a place in my little house and like the look .I want to refurbish the whole thing and change all elko . The amp section works fine , control for balance , treb& bass now run with no scratch sound .I've connect a cd player , sound good
But the tuner does not works properly ; on FM only few station can be hear ; these are weak with lot noise and no one has the strenght to light the stereo decoder .I've check solder point and correct but don't need it ; just to see if will do better ..but nothing Then I've "hammer"PCB with screwdriver to look for bad contact ... no way .So , with schematic I've read DC voltage on front end side : they are correct .I've experienced with AF but never "tuned" a tuner . I've scope , thd multimeter but no HF generator / analyzer Do someone did a repair on this 901 ? could give me some advice please?
Was the problem present before you started work?They usually dont go out of alignment by themselves.Either someone messed with the alignment or something has gone wrong in the tuner frontend or IF stages.You could check the voltages and signals around IC TBA460 - though this IC rarely fails.It's less unusual to see the frontend FET go weak. Tim wrote about it at some point on Beocentral and suggesteda replacement FET and some modifications, but it may be a lot easier to simply replace the complete frontend module with aknown good used original module than attempting repairs and aligninment to the defective module.
Martin
Thanks for reply Martin ,yes the unit was stocked for years and I lit a week ago .Just noise and very far station .Alignment is still original , no one seem mess with adjustment but some trimmer are very scrapped .Voltage around the tba460 are around 20% lower than on schematic (fm mode no bracket value ) but no fm signal on input , just dipole .Today I spent some time and start replacement with new pot for R9 (I've read the value on PCB for near value position)And some elko around front end / decoder ; the orange caps .They seem fine and esr & cap are ok.turn on , now I've tuned some station , great improvement .I don't think that the replacement all tant caps around will go better . Anyway the fault seem caused from component deterioration .In green part replaced for tuner ; in red still in progress AF pcb
Play a cd from input sound fine .
system down ,, I can post picture ..will try later
many thanks
I suggest you replace those Ducati capacitors. Ten in total.They may not be the reason for the fault in question, but they will cause problems - sooner rather than later.
The three large electrolytic cans are not original but may be fine.
Check the power supply voltage adjustment. It can cause strange problems if far off.
The not original parts (in red on picture ) has been changed by me few hours ago .
But now It's frozeen in garage
The unit was original ; go for ducati .
I can not find replica of antenna wire connector , with 2 spade . I have lot a receiver but got only one .
When will change all others parts will be check bias again I give feedback
Gabriele
ciao ,
After a healthy recap things get better station are stronger but no way to light stereo lamp .
Great improvement has been reached when test some resistor in fm path .
Some resistor measure 50% off value , they are most 1/2W carbon ; now the receiver get FM STEREO station
Now I'm getting into restore a BM4400 !
some resistor :
https
https://imgur.com/a/jd89mLt
Hi ,
Thanks for your thread who helps me, i have similar problem, (weak FM) and for me it's the TR1 in FM section (MPF120) who is dead
you can see my topic https://archivedforum2.beoworld.org/forums/p/50192/352469.aspx