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BRONZE MemberALF, those jumpers most definitely need to be removed as they are shorting the inputs to the outputs which will cause oscillation. Glad to see you got it working, Enjoy!
It’s not really a mystery as a short will not take out your cartridge coils since they are not conducting current. If you are reading 6V DC on each of the + and – inputs then the passive components are likely fine, and your issue is the ICs. You should use hot air and flux to replace the ICs. There are plenty of YT videos showing how.
Actually, pins 2 and 6 are the feedback loop inputs and not the signal inputs. Pins 3 and 5 are the inputs and 1 and 7 the outputs. I don’t know what you mean by “checking the inputs” because putting a probe on an input of a high-gain stage will produce an audible side effect. Given how inexpensive these opamps are, unless you find a burned part, it is easier simply to replace them as long as all the voltages check out.
There are 2 voltages going to the board – 22v and 12v. First, I would unplug the board and check that the power supply is outputting the correct voltages. Then after removing the power cord, I would reinsert the RIAA card and check the voltages on it per the service manual. Make sure you check for 12v on each IC. Since each IC is amplifying both channels, a bad one can impact both. If you have an oscilloscope, you can check the nature of the noise and the point in the curcuit that it is originating from.
Assuming it does not have a phono preamp board, it depends on what input you are connecting to. If you are going to a DIN Phone input, you need a 5-pin DIN cable. If you are connecting to an RCA phono L/R jacks, you need a shielded pair plus a separate chassis ground wire.
In the US there were no finish choices. The base was a dark gray matte plastic.
If you do not have continuity between the cartridge body clip, board ground, chassis ground and external ground wire you will get hum.
Across the many 40xx turntables I have serviced, I have never replaced the pulley of a working motor. You’ll be fine with the proper belt and shaft pulley.
There is no need to replace the motor pulley if it is not cracked or deformed.
It looks like your tonearm’s azimith adjustment is way off with the left side too low as viewed from the front. There is a separate adjustment in the manual for that.
The motor circuit requires the 15v supply to operate. The TURN button is used to rotate the record for cleaning, not the 33 speed button as was the case on the older models. The 45 button never turned the platter.
Are you getting a voltage change when you press start on pin 38? Do you have 5v on the collector of TR21? I would also double check your replaced cap polarities against the schematic (not the board).
I can’t tell from your third cropped picture, is the rear of the tonearm even with the detector arm and its only the rear of the arm that cannot go done enough to raise it?
The fact that it is silent when the mute switch is engaged is indicative of an improper ground configuration. This can happen when cables are replaced. With the table unmuted and the RCA cables disconnected, take the following measurements with an ohm meter:
- Measure between the ground wire and shield of each RCA and you should see an open connection >1Mohm.
- Measure between the ground wire and the ground of the circuit board and should read 0 ohms.
- Remove the cartridge and measure between the ground wire and the copper tang at the end of the tonearm – should read 0 ohms.
If any of the above are not correct, you can get a hum.
I would first check the cartridge coils which can be done by measuring between the R & GR and the L & LG pins. Depending on which cartridge you have they should measure between 800-1K ohms for each channel. I would then check that the RIAA board is getting 12v especially the collector of TR2 which is a quad bilateral switch IC that also acts as a mute. If the 12v is not on available from TR2 to pins 5, 6, 12, & 13, then you will not get sound even with a good cartridge. You should also have 12 on pin 8 of IC2 and IC3.
I don’t believe you are measuring the correct contacts with those results. The muting switch is different depending on whether you have the version with the built-in RIAA preamp. In either case, when the tonearm is up, you should get 0 ohms or .1. This is a two pole switch meaning there are two sets of contacts. With it down, you should get 800-1K ohms w/o the module and around 5K-7.3K ohms with it depending on the input impedance of your amp..
Your hum issue is likely an improper ground between your turntable and amp. Does your 2400 have a DIN cable or RCA Phone cable. If the former are you using a proper Phono DIN to RCA adapter with a ground wire or are you connecting to a phono DIN input?
I have not observed your problem, but would approach troubleshooting to understand which circuit is at fault as it could also be the record detection section. TR4 and 5 are simply switches so they do not need to be matched. Check the action of the mute switch and check whether it is unmuting or staying muted as it transitions from lowering to raising. I would also check how it behaves with a 45 and without a record at all. Finally, I would monitor the base of TR% to see whether it is causing the arm to raise immediately. Report back with these results and I may be able to recommend either a fix or further testing.
I too have that set and do not experience any problem. If you do not switch the speed and treat is as a 33 record, does it set down correctly? If it does, then I believe it’s a power supply issue with the higher current or faster rotation causing the detection circuit to malfunction. You can confirm this by using your 185 gr 33 record and switching the speed in the same way you did with the 45.
It can be several items, depending on what you are specifically observing. Most of the time, if you hear the muting relay immediately but not the normal solenoid sound, it can be the horizontal or vertical pivots for the cueing mechanism gumming up and not moving easily. It can also be a residual magnetic buildup in the solenoid. This can be handled with a tapehead demagnetizer. If you hear the solenoid but the arm is lagging, this can be because the return spring has weakened, the damper cylinder is not moving smoothly or adjusted properly, or the vertical pivot is gummed up.
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