This thread covers the complete restoration process of the SONY TC-K411 deck including both the mechanical side and calibration of the electronics (which is needed, despite the external cal feature). Parts you will need: 1. New belts: https://webspareparts.com/products/sony-tc-k411-belt-kit-for-cassette-deck 2. New pinch roller (uses the standard 13x8x2mm one): https://fixyouraudio.com/product/pinch-roller-13x8x2mm/ 3. New gear for the secondary motor: https://fixyouraudio.com/product/sony-tc-k411-motor-gear/ Oil used should be watch oil. The belt kit from webspareparts is the one I used and was very happy with it: wow&flutter obtained was 0.062% WRMS (lower than the 0.07% WRMS spec). MECHANICAL SIDE: 1. Start by removing the top cover held on by 4 screws; 2. Remove all the cables going from the front panel to the PCB (marked in red on picture); 3. Remove the screws holding the front panel on; 4. Remove the front panel; 5. Remove the deck itself from the front panel (it's held by 4 screws + the cassette door cover); 6. Remove the top PCB from the deck; 7. Remove the motors assy from the deck; 8. Clean all the old belts residue and the pulleys; 9. Lubricate the capstan bearing (pay attention there is a plastic washer on the opposite side); 10. Lubricate the motors top bushings; 11. Take the PCB with switches out, remove the plastic covers on leaf switches and clean them with contact cleaner and cotton swab; 12. Replace the gear on the secondary motor (should be replaced even if not fully broken); 13. Put the new belts as indicated on pictures; 14. Reassembly the motors assy and slip the new belts back onto their respective pulleys; 15. Replace the pinch roller as indicated in pictures; 16. Clean any oil residue on the capstan remained from lubricating the capstan bearing; 17. Reassembly the deck onto the front panel; 18. Remove the potentiometeres board from the front panel and clean all the pots with contact cleaner; rotate them 20-30 times full rotation to make sure any oxidation is removed; 19. Reassembly the front panel back onto the deck and re-connect all the wires;
On the electronics side, it important to ajust the following: 1. Playback level (this is usually the most off and very uneven between channels); 2. Record level 3. Bias Record level and bias should be ajusted because the external adjustment is one for both channels, so if there is any channel imbalance, you cannot compensate for that using the external pots. What tape you use for this adjustment is oviously not critical (as you will adjust futher using external pots), so use a tape of your own choosing, but prefferably one that has not been recorded before for best results. ELECTRONICS SIDE (note adjustments should be made in the order presented): 1. Playback level SONY specifies the playback level on the LINE OUT (loaded with 47k) should be 320mV RMS with P-4-L300 tape (160nWb/m DIN). This translates into a 437mV RMS when using a Dolby level tape (200nWb/m ANSI), which is what I recommend using. Note it is very important to load the LINE OUT with 47k, otherwise your levels will be incorrect. TRIMPOTS: RV121 (left channel) and RV221 (right channel). EDIT: Due to inconclusive results regarding posts below, I recommend adjusting levels at the Dolby IC instead. With 200nWb/m ANSI tape, levels should be 388mV RMS at RECORD OUT pins (no load). 2. Record level With both external calibration pots put on center point (where they click), feed the device with a 315/330Hz test signal. Adjust it to -10dB on the VU-meter. Monitor the line out using a TrueRMS multimeter or digital oscilloscope (remember to load the output with 47k). Note the voltage when unit is set to SOURCE. Adjsut the internal trimpots so the TAPE has the same level as the source on both channels. TRIMPOTS: RV101 (left channel) and RV201 (right channel) 3. Bias With both external calibration pots put on center point, feed the device with a 10kHz test singal. Adjust it to -10dB on the VU-meter. Monitor the line out using a TrueRMS multimeter or digital oscilloscope (remember to load the output with 47k). Note the voltage when unit is set to SOURCE. Adjust the internal trimpots so the TAPE has the same level as the source on both channels. TRIMPOTS: RV103 (left-channel) and RV203 (right channel). The tape speed should also be check and adjusted if necessary with the trimpot located on the deck itself (not the trimpot on the motor). The one I repaired was pretty close at 2995Hz and I adjusted it to 3000Hz, despite it would have been perfectly fine without adjustment.
Valentin, very nice tutorial: I'm amazed you find the time between many Walkman tutorials and this cassette deck tutorial, excellent work! And I truly appreciate the technical guidance: I found this tutorial while looking for information on a problem I'm having with my Sony TC-K71:
Hallo Valentin. Is it possible to adjust the speed without any precise measure instrument? If yes, where are the speed adjustment tripods?
It's always possible to adjust by ear, but it's something I don't recommend doing as it's not an accurate method of adjusting it. Adjustment trimpot is on the back of the motor.
Hey Valentin, I have been following this excellent tutorial in order to tune up a Sony KA1ESA deck, which has a similar mechanism and electronics to the K411. To set the playback levels, I'm using a Dolby level tape (see image) that I believe you had recommended in another thread. Loaded with a 47k resistor, I was able to get .42V on the digital oscilloscope, but the left tuning pot on the deck was at the very limit of its range in order to reach that. The resulting sound is good, but I am noticing that the level meters on the deck show the signal to be several dB hotter than they appear on my D6 (which I recorded the music on). The service manual for the KA1ESA states a Line Out level of -7.7dB for Level Adjustment. Is that essentially 0dB with the 47k load? And the 0dB 315hz tone on the Dolby tape should translate to 421mV, same as your K411 example?
Fact you need to turn the trimpots close to the max setting to get the desired value indicates something is wrong. There are a couple of things that can be wrong including: line amp level dropping too much when loaded, incorrect line amp gain or even an error in the service manual (which seems unlikely in this case, but possible). As far as that WLA-PBD1 tape goes, would no longer recommend it since the one I used had some imbalance between the L and R levels. Besides, this tape is no longer made. HPR tapes are a better choice, the 218nWb/m (position 5 on the list): https://www.ebay.com/itm/176013927759 These tapes are DIN, so the 218nWb/m DIN corresponds with 200nWb/m ANSI. What I would do in this case is measure the level at the output of Dolby IC to eliminate some of the potential problems mentioned. Levels at the IC should be 388mV RMS at RECORD OUT pins. Level calculated for 200nWb/m was wrong (added only 2.4dB instead of 2.7dB), correct level is even higher at 437mV RMS. Edited post #2 as well.
Thank you Valentin, I have ordered the HPR test tapes and will try again with those. The 30 pin chips on these boards (marked as Dolby PB on the board, and Dolby-S in the service manual): are they the ICs to measure?
Also, unfortunately I found a small plastic washer (clear, slightly pink color) after I had reassembled the tape mechanism and have no idea where it came from. It is not the capstan washer (which is installed) and the only other washer on the mechanism is indicated as Part 121, the same in the TC-K411. I can't quite make out where the SM is indicating that this washer goes - have you any idea?
Part 121 looks like a shim to adjust erase head height or a cable holder. Would assume you didn't remove the erase head, so your washer is likely coming from somewhere else. As far as the adjustment goes, measurement is done at pins 22 and 7 of IC341, which I realise in on back of the board SMD. However the output of this goes to pin4 of the Dolby S daugter boards, so you can measure there instead. See pictures attached.
No, didn’t touch the erase head, so quite confused about where this washer came from. I did pull out a bag of spare parts I have from an old disassembled deck to replace one of the leaf switches on the KA1ESA - right before I found the washer - so there’s a chance it came from there. I still don’t see what Part 121 is meant to be though. Thank you for the detailed indication on taking the reading from the Dolby chip. My service manual is a black and white copy, so hard to read what is top and underside of board! I will check that with the Dolby tape.
Ok, i see this now. Rather hard to photograph, but the washer behind the erase head is clearly in place.
Hey Valentin, so, as you kindly advised, I tried measuring off pin 4 on the Dolby S daughter boards while playing the WLA-PBD1 Dolby cassette. I was getting crazy VRMS readings on the little digital oscilloscope I have: like 7.4V RMS on each of the channels. I adjusted the Playback pots and got that down to around 3.24V, before realizing that was still x10 times too high for the target of 324mV! I have a Fluke multimeter that is non-RMS, but that has a mV range, so thought I would try that: it actually gave readings close to 324mV directly off the Dolby chips with nothing plugged in to the line out on the cassette deck. And interestingly, the meters on the front of the deck showed the channels right at the Dolby mark on the VU when I had this 324mV reading with the multimeter. But when I play back a known good tape, the volume (and dB on the VU) are noticeably too low! I can wait to troubleshoot further when I get the HPR calibration tapes. And in the meantime, I'll take a look at the oscilloscope and double check it is calibrated correctly. Thank you again.
Something seems off. Assuming the same WLA-PBD1 tape was used to calibrate both the known-good recorder and this deck, the tape itself shouldn't be the problem. As even if the tape had the levels off, it would be off by the same amount on both, so you shouldn't notice any difference (on VU-meter or audible volume). At least not with unloaded line out, assuming it would be a loading problem. On the other hand, VU-meters and headphone amp are fed from the line amp, so any incorrect (lower) levels on the line out will be reflected in a lower VU-meter reading and lower volume. For Dolby decoding it's important what comes out of the Dolby amp, the rest isn't important to the decoding process.
Just to clarify: the known good recorder is a Deb64 refurbished D6, and the tape a recording made on the D6 with a NOS chrome tape. It displays peak audio levels around +4 to +6 on the D6. This is my first attempt to calibrate the KA1ESA. I bought it used, but there was never any electrical issue that I noticed with levels until recently when it developed a channel imbalance - hence my attempts to calibrate following your tutorial. On the measurement off the Dolby chip: I did notice a slight difference in levels depending on whether there was a cable attached to the RCA outs (regular phono cable, no load) and when there was no cable attached. What is considered best practice for setting levels? As, in use, there will always be a phono cable attached, I assume levels should be set with one attached?
This wasn't a good idea in my opinion. Unless the unit was dropped, there's little reason to suspect the trimpots moved by themselves causing the imbalance. Usually when the calibration is off, it's like that from factory. Wear and tear + drift usually cause only minimal deviations. In regard to the slight drop when connecting a cable to the output there shouldn't be any significant drop (variations of 2-3mV should be ignored) at the input of line amp when connecting a load (resistive or capacitive - cable has parasitic capacitance) at output. That line amp is there to isolate the output of the Dolby one (as it probably doesn't have enough drive capability) by connecting it to a high impedance load (input of line amp). If you have a singificant drop at the input of line amp while connecting a load (being it cable - capacitive or the input of another equipment) and assuming the Vcc is fine and feedback resistors are fine, would change the op-amp. Something seems off by a lot given you need to make the output 2.28x (7.4V/3.24V) higher to sound right and display right on the VU-meters. This factor is way too high to account for any normal loading effects.
Just posting a belated follow up on the calibration of my KA1ESA (cousin of the K411). Starting over with the Hans Peter Roth Dolby Level tape and a remade 47k load cable, I have been able to achieve the target 437mV RMS on line out. Checking voltage on pin 4 of the Dolby S daughter boards (which receive the output of the main Dolby IC), I am getting readings of around 392mVRMS at the same adjustment settings. That’s higher than the 324mV that you had said to adjust for @Valentin , but looking at the data sheet for Dolby IC CXA1563M, which the KA1ESA uses, the test voltage is stated as 388mV (at the REC Out pins)*. The unit's VU meter now shows peaks much closer to those on my D6 for known good tapes, both chrome and normal tapes. Am I good with these levels, then, before proceeding to check bias and record settings? *(Note, the CXA1331S Dolby IC chip that the K411 uses also states to test for 388mV at REC Out pins.)
One slight anomaly remaining on the Playback Level settings: when I set the voltages as described above, the VU meter on the deck displays a stronger left channel when playing back the Dolby Level tape, despite mV readings at line out and Dolby chip being equal left and right, see pic 1. That is when working with the deck disconnected from my receiver and speakers, and with no load at line out. However, when I reconnect the deck to the tape loop on my receiver and switch it on, the VU meter drops down in the left channel to read as balanced, left and right, as in the second image. Switch the receiver off again (or just turn off Tape-Monitor), and the VU channel imbalance returns. Voltage from Dolby chip remains the same, whether the deck is connected to the receiver or not. (Note, my receiver is a modern one: tape loop is not in-circuit when the receiver is switched off.)
As long as the voltages at the Dolby chip don't change, you're fine as far as the Dolby decoding goes. Read the Dolby IC datasheet myself, will correct the values stated at post #7. There are likely errors in the manual. It's the datasheet IC that is the most reliable source of information. As for line out, the M5218 op-amp has a pretty high output drive capability (can supply up to 50mA and has a slew rate of 3V/μs), so driving a 10kΩ line in shouldn't be a problem. As stated previously it's possible there's something wrong in the line amp circuit.
Thank you Valentin. So that op-amp is IC395, is that correct, close to the line outs? It's a M5218AFP, and seems to be plentiful available online. But again, it is surface mounted on the underside of the main board on the KA1ESA, so getting at that to change it will be a challenge.
