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Hi all can anyone with knowledge of these items advise on a fault i have withe the phono section, ive done extensive repairs to it including tape section repair and radio, output amplifier repair but i can only get quiet output on both channels even on max volume from what i can fathom out i am getting a muted RIAA preamp issue . i can be more specific to anyone who replies.
Regards Maurice
The RIAA pre-amp is sited on the board beneath the turntable toward the front of the unit,you'll need to remove the plastic moulding to access it.It's supply is shared with the tuner,so the fact that your radio section is functional,seems to exonerate that.Check the supply at the board,it comes in on P2-pin 1@42v.
On the board there is a regulator and decoupling cap that may need investigating(TR40,C41)The emitter of the regulator should be at 35v.
It may be a silly question,but are you confident that the pick-up cartridge is ok?
You should be able to "blip" the inputs to the RIAA pre-amp at P1 pin 5 and pin 3 to see if you get a corresponding buzz from each channel?
If you do,it definitely points to the pu or perhaps sheared connecting leads to the pu arm,they are rather thin and vulnerable.
I like these little units,they work well.
Nick
Hi Nick
thanks for you informative reply, i can confirm the cartridge is ok its new from soundsmith. I've checked the voltages on PCB 19 you mentioned i have 42v P2-pin 1 and 35v on TR40 as on diagram , also have checked the 35v on the L/R channels of the preamp at R104-204 thats ok too. what i did find was a resistor R36 (10k) which had a burn hole in it (although out of circuit it measured ok) this esistor is tied to pins 5&6 of IC 3 HEF4001 NOR gate ic . pins 5&6 are controlling tonearm lift-mute function via S3 would it be possible that IC3 has failed there is 11.4v on pin 14 of IC3 as per diagram. note i do get very quiet output on P2 pins 3-6. Also on PCB3 IC5 audio in and out is present ( very quiet ) as i mentioned on first post i can get feint audio reproduction at the speakers when on full volume. tape and radio output are normal. like you i enjoy these units i love the styling perhaps autoreverse on the tape would of been a better choice but seeing how much pcb wise is crammed into a beocenter 4000 i understand why b&o opted for a single side tape mech, Any pointers or help very greatfully received
Yes indeed,it could be IC3 as it seems to be dedicated to the arm raise/lower muting function.Before condemning the chip though,it's well worth checking the microswitches S1 and S3 for oxidised contacts.
These are the "mech sensor" switches that indicate where the mech is at any given time,and may not in fact be working properly,leaving the amplifier permanently muted in phono mode?
You could check the action of the switches too,to make sure that they engage at the correct point.
If you have a logic probe or oscilloscope,you could check the activity at P3 pin 8 and 9 when the arm raises and lowers.
Its a good 'un sir,be interesting to sort it out
checked the switches as you advised and cleaned with thin strips of 600 grit ive ordered the logic chip and i will keep you updated when ive received it and fitted it. Fingers VERY crossed.
Any progress with the whispering yet Maurice?
as promised heres the update on the phono issue, I replaced the logic ic which didnt cure the problem (after waiting 5 days for one that didnt arive from ebay and re-ordered another one) so after carfully checking the and resoldering the fine wires to the first pcb from tonearm and got eventually rh channel working normally but no left channel then i got lh channel working but no rh i even fitted a riaa preamp directly to tone arm and that produced the same intermittent results so the tone arm wiring has been damaged internally. today i won on ebay another 2200 with a working phono ive tested it , so i will swap it over then hopefully all will be resolved this one has been a pain to fix. fortunatly the owner is prepared to cover the costs. so thats about it on this saga. thanks so very much for the information and advice.
now to finally wrap up my beomaster 1900 it sounds great after dillens cap kit has been installed and ive replaced 2tr300 to get a full range of tuning on the fm scale. its a great feeling getting stuff up and running.
regards Maurice