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BRONZE MemberThose do not look right. Measure the cartridge pins when it’s not installed. The pins are looking from the back: L+. R+ L- R- The 740 ohms should exist between L+ to L- and R+ to R-. There should be no resistance between R+ and L+.
Unmuted; When the cartridge is fitted to the arm, the two coils have their respective negative ends connected to signal ground. This means that if you measure from L+ to R+, you measure the two coils in series (2x 740 = 1480). All fine. Muted; All cartridge pins are connected to signal ground. All fine. Martin
Martin, I agree but the diagram is still wrong as a single pin cannot have 1480 and .2 ohms. It would be 1480 and 740 ohms.
Those do not look right. Measure the cartridge pins when it’s not installed. The pins are looking from the back:
L+. R+
L- R-
The 740 ohms should exist between L+ to L- and R+ to R-. There should be no resistance between R+ and L+.
BRONZE MemberThe muting switch shorts the signal to so your ohm readings are correct. What you need to measure is when the cartridge is plugged into the arm and the switch unmuted you should see around 800 ohms on both channels.
I’ve not worked on one but I believe from the manual that there is a snap on LED cover that you remove to release it and the wire stays attached to the LED.
To narrow down where the fault lies try all sources to see if the channel is missing from all or just one or more. If all, then I would look at the preamp area prior to the mono switch and check for bad solder joints especially a the board connectors.
I addition to Guy’s excellent tips, if you have a multimeter you can measure the resistance between the top and bottom pins of each side of the cartridge. The readings should be a within 2% of each.
The section hcraig244 posted is correct.
Check the link in my first reply to you for the relay.
As long as the cartridge body (coils) is fine you can simply replace the stylus. The SP-9 was the elliptical version of your SP-7 and is available on the web such as https://www.lpgear.com/product/BOSSP09.html.
The ring is just an indicator. You rotate the weight which is the cylinder behind.
That appears to be Figure 142 and part 257022 Arm, Speed in the manual.
You need one which is “NO” for Normally Open and is DPST with the correct pin-out.
If they spliced the cable, then you can connect the ground wire to the braided shield of the DIN cable. As to replacement cartridges, your SP-6 has a conical stylus. An SP-12 would be better; however, I do not know why you’d have an issue with the tracking weight of an SP-10. Do you have a stylus gauge? What range are you able to set?
Looks like a nice find! If you take the bottom off you will find where the RCA cables were attached as well as the terminal that is grounded to the chassis where you can simply solder a stranded single wire for your ground. As for belts, check out https://www.beoparts-shop.com.
It most definitely can blow as those contacts conduct when you plug it in.
Before attempting to disassemble the transformer, I would measure the primary and secondary windings with an ohmmeter. This will let you know whether it has opened. If there is resistance on both sides then you can simply hook up the primary to a raw power cord and measure the secondary voltages. If they are fine I would look deeper into the power supply.
I would check whether there is a short instead of a 4ohm measurement. You would need a multimeter.
B&O made the switch of sides in all of their turntables in the mid 1980’s. They still perform the same record detection function. They became wider to display the speed while the cartridge carrier became narrower to support the smaller cartridges. The older service manuals for the 400x series provide the most detail on the tracking system.
By muting the unit I meant going into standby. The relay does not switch all the power off.
First you need to confirm that your standby voltages are fine. TP9 should read 6.5v DC. You should also have 5V DC at pin 5 of the P11 connector. If those are fine, then you likely have a fault in the power amp section that is muting the unit. There is no need to replace the relay as what you have observed is its normal operation.
Finding a fault in the power amp circuit is more difficult since the +/-30v supplies share the same board and there is no easy way to disconnect the power from one channel without pulling the output transistors. Since you are able to get it on for a time, I would try looking for a DC voltage on each channel w/o speakers connected while the relay is engaged and figure out which one is tripping the fault circuit as a start. This all assumes the 6.5 and 5v supplies are fine.
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