[Mark-sf]

If you do not have continuity between the cartridge body clip, board ground, chassis ground and external ground wire you will get hum.

• This reply was modified 1 week, 2 days ago by Mark-sf.

[Mark-sf]

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.

[Mark-sf]

There is no need to replace the motor pulley if it is not cracked or deformed.

[Mark-sf]

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.

[Mark-sf]

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.

 

[Mark-sf]

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).

• This reply was modified 3 weeks, 4 days ago by Mark-sf.

[Mark-sf]

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?

[Mark-sf]

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:

1. Measure between the ground wire and shield of each RCA and you should see an open connection >1Mohm.
2. Measure between the ground wire and the ground of the circuit board and should read 0 ohms.
3. 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.

[Mark-sf]

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.

[Mark-sf]

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..

• This reply was modified 1 month ago by Mark-sf.

[Mark-sf]

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?

[Mark-sf]

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.

• This reply was modified 1 month ago by Mark-sf.

[Mark-sf]

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.

[Mark-sf]

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.

[Mark-sf]

The arm does not “see” the record when it gets to the drop point. This is controled by a black line on clear plastic guide attached to the arm transport. This guide can be adjested left and right to correct the set-down point for 12″ records though you need to remove the top plates. As to why it works on 33s bot not that 45, have you seen this occur on any other records? How does its thickness compare to your 33s? There is something about it that is causing the  light bouncing from the record to pulse telling the arm that there is no record there.  It is possible that the sensor circuit is mis-adjusted and the service manual describes the procedure but you do need test equiopment. One final possiblity is that your power supply has bad electrolytic capacitors that is causing a ripple in the voltage feeding the lamp and so the lamp is pulsing. If the 45 record is of different thickness or reflectivity, this could explain why it only happens on that one.

[Mark-sf]

I’m not sure what behavior you are describing. The turntable only detects a 45 record by virtue of it “seeing” the smaller diameter by receiving optical pulses from the ribs until the edge of the 45 is reached. Just prior to that a black line on the clear plastic mounted to the arm transport causes the speed to switch to 45. If you put a 45 12” record on the turntable should behave as if it’s a 33  LP and simply set down on the edge. You have to manually switch to 45 speed. Please describe what happens if you simply put the 45 LP on as if its is a 33 and change the speed right when or shortly after it lowers. If it is not lowering but continuing on, is your LP a colored vinyl that is partially transparent. This can cause it to not drop but is normal. Simply stop the arm with the > control and use the cuing to manually lower.

[Mark-sf]

You can get an extractor tool cheaply. – i.e. https://a.co/d/j3yLCnU. If you are trying to terminate the wires with new pins, that requires a special crimp tool and new pins and housings are available in kits.

 

[Mark-sf]

Yes you do unless the powered speakers have a dedicated phono input.

[Mark-sf]

This depends on your version. If it has the RIAA preamp, then it is pin 7. If not and you plug in into the Phono input of your receiver, it is pin 6.

[Mark-sf]

filip_kbh wrote:

Yes, I have all 7 pins. The switch under the front panel PLAY button was very corroded. I cleaned it but it is falling apart, and I can’t seem to position it correctly for it to work when I press the PLAY front. After fiddling with it for hours, I have decided to accept that it doesn’t work. Can I replace it with another type of tactile switch? It seems to be a rather cheaply made board where a piece of tape was holding the metal plate in place. Any suggestions?

It is simply a piece of conductive spring metal that should be able to be cleaned if desoldered. You could switch it with for example the 45-speed one if its damaged. A pushbutton microswitch such as one of these should be able to be retrofitted with minor board modifications, though I have not personally tried it.

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