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
I sent my daughter a perfectly good RX2 turntable and mmc4 cart but for some reason it's now back with Dad and not working. Symptom is silence.. neither channel produces any music and I've changed carts to a known mmc2 an still no sound output. It's a beautiful piece. Mechanicals are solid but I'm wondering where I might start my troubleshooting? I have the service manual and am fairly competent to trace simple things but don't have an O'scope or signal generator.
I've got it hooked up directly to my Pioneer A-27 (Series 20) Amp/Pre-Amp on Moving Magnet with cartridge load 150 pF and 50K ohms input. I've seen posts elsewhere on B&O TTs where the mute relay rusted or fouled and sanding the contacts was successful but I haven't cracked it open yet. Just tested the RX2 side by side my TX2 TT and swapped the mmc2 cart so I know the cartridge is working properly.
The mute actually shorts the leads of the cartridge so the test is to use a simple VOM to measure the resistance of each channel which should be ~1000 ohms when sitting on the record.
So measure between pins 3 and 2 (gnd) for Left channel and 5 and 2 for Right and should be ~1K Ohms? That's a DIN connector pictured here but the unit has RCA plugs so measure between center pin and ground at the output?
Yes, between pin and shield of each RCA.
Does it make a difference if the cartridge is installed when I test? I assume so...
Yes it needs to be installed and lowered to play a record.
Connected the Simpson Meter and measured 0 Ohms before the record is played. As soon as the record plays the resistance goes to infinity... happens on both channels at any R setting (x1, x100, x10,000). I can hear the relay apparently operating at the correct time. If I'm looking for 1K ohms something isn't right.
I tried both mmc4 and mmc2 which both produce sound properly on my Beogram 3000.
The fact that both channels are open (infinite resistance) is point to your tonearm wiring. That wiring is most vulnerable in the area of the tonearm bearing assuming no one has been inside. I’m afraid you will need to physically inspect along its path and will likely need to repair as I have only ever retired their linear tracking models which is easier. This is job for a qualified tech as trying to rewire the entire arm without damage requires removing the glued cartridge mount. Given the age of the table if the break is not in an area that can be spliced, I would recommend finding a replacement tonearm from a parts unit. Once again this requires an experienced tech.
That is not a desirable result! Thanks for this. Maybe I'll sell for parts or see if as you suggest there's a dumpster dive for me on eBay.
Not knowing how this player is build... If you already know that cartridge is ok and you have multimeter to measure resistance. Just take the cartridge out and I assume you see connectors. Then in the other end of arm must be wires coming out. Are they visible ? Might be 4 of them. Measure resistance of all of them, the correct wire shows 0 oHms if it is ok. Check those wires like that, you shoud get 4 results with 0 oHms. Do also crosscheck that the wires are not short circuited.
Ismo
I disassembled the top and took a look at the tonearm. The wires from the arm to the 8005073 Board (Muting PCB4) are solidly connected. Upon further look it seems the break(s) are likely at the head, where the black plastic cartridge receptacle meets the metal tonearm tube. When I touch it there's a gap that easily forms so my guess is the wires are severed at the head.
Pictures attached.
Pic of wires attached to pcb
Tonearm receptacle "gap" where wires likely broken??
How do I remove this from the metal tonearm? Heat gun and slight tug??
It is possible that someone may have tried to remove the cartridge by “unscrewing” it thereby stressing and breaking the connections at its socket. This would be evident if the junction of the black holder and arm tube were loose. Assuming one can remove the holder, I am not familiar with how the wires were attached as I’ve never attempted this type of repair. B&0 only offered the arm complete as a part.
Don’t bother trying to repair vs, replace. Note the sonic weld along the sides. Likely the connector was first wired and then the halves welded. Unless the break occurred downstream from the connector you are out of luck. The only safe way to check is to totally free up the other wiring end giving it a few inches of slack before attempting to remove the mount making sure you label the wires. Heat is a problem as you can easily melt the plastic. Careful rotation may be the better choice to break the glue seal but it’s hard to prevent torquing the arm bearings and holding such a thin-walled tube without damage is no easier. While you technically have “nothing to lose”, unless it is already free to rotate, I don’t see a path to success. Perhaps there is someone who has done this, but I would not have attempted it when I was a tech.