High frequency probe, high frequency line can be customized with other specifications

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Changhong Color TV Repair: Common Faults and Solutions
1. For the LA7688N decoding block in Changhong series TVs that shut down, try removing the Y board (viewing board) VD611 and VD612, then back-weld a 4148 diode, connecting the positive end of VD613 to the B pole of VD617.
2. In the case of Changhong 29A18, if the line size is not full and the main power supply only reads 75–85V, check the power supply part and replace RU2 if VD520 is faulty.
3. For Changhong CK56B2–22", if the field vibration occurs and TA7698 has only 4V at pin 33, it might be due to an open circuit in the push tube or transformer.
4. On Changhong 2939FD, the upper back sweep appears, and entering the "S" bus returns to ABK--ENABLE. When the fault occurs, brightness increases. Check the comb filter for faults and re-solder if necessary. Note: Removing the button socket may cause automatic channel flipping.
5. For Changhong N2918, if there's only a blue background and no picture when AV input is used, but sound is present, adjust the AV fine-tuning. After repeated checks, the comb filter is likely faulty. Re-soldering resolved the issue. It’s estimated that leakage capacitance was involved.
6. For Changhong C2589, black lines appear in the upper part of the screen. After checking, replace the C329–471K polyester capacitor to restore normal operation.
7. Changhong C2191 produces a "zhi" sound and doesn't work. Unplugging the deflection coil shows normal C voltage. Upon investigation, C428–1UF/250V is shorted and needs replacement.
8. Changhong C2992 has jagged images on the top. The field supply capacitor C825 (35V/1000UF) is normal, so no action is needed.
9. For Changhong G2125, the upper half of the image is distorted. Checking R402 (120K) reveals it's open, and replacing it fixes the issue.
10. On Changhong 2118FA (A6 movement), VD514 (4148) is open. With a dummy load, the main power supply is normal, but the tube burns after 2 seconds when the load is applied.
11. For Changhong C2919PK, the TV has power indication and standby 50V, but fails during second boot. Checking the line output load (pin 7) reveals VD408 (RU4Z) is shorted. Replacing it restores normal function.
12. Changhong G2132 (K) shows power but no secondary boot. The line isn’t heated, and with a dummy load, the main voltage is 130V. After repeated checks, the deflection coil is found to be shorted. This is a common failure for this model.
13. For Changhong R2916N (R2518N same), the line center shifts right by 3cm, and no characters are visible. Checking D403 and D404 (pins 9) shows they are shorted. Replacing D404 (5.1V) resolves the issue. The negative end of D403 should normally read 0.7V.
14. On Changhong 25K18 using LA7841 field block, the upper part of the image compresses, while the lower part is thin. Checking C301 (1000P) reveals it's faulty. Replacing it fixes the problem.
15. For Changhong G29K36, a bright line appears at the top. Check N30 (LA7841) and VD302 (1Z75). If VD302 is shorted, it could damage LA7841.
16. Changhong 25N16 has a 10cm compression and rolling. Replace C302 and 10N capacitors to fix the issue.
17. For Changhong C2919PK, two types of retrace lines occur. For one, replace C318 (35V/220UF). For the other, change C305 (50V/1UF).
18. Changhong C2919PS has stripes and a black screen. This indicates a faulty comb circuit.
19. For Changhong C2588A, a rare compression failure is resolved by replacing C317 (2.2UF).
20. Changhong C2169 displays a red “M” character. This means it entered debug mode. If remote control cannot exit, press an unused button between “SYS1/SRC” and “AN-SEL” on K1L remote to turn the red character green. If the issue persists, replace the remote.
21. Changhong C2169 and similar models enter AV mode. This usually indicates a memory or external circuit failure. Replacing the affected components typically resolves the issue.
22. For Changhong R2518AE (D), the TV has instructions but won't boot twice, and the tube burns. Checking the line frequency 15625 reveals it's causing the tube to burn. Replacing VD431 (1N4148) fixes the problem.
23. Changhong C2588PS has small retrace lines in the upper part. After checking, the field blanking is bad. Replace R321 (2.2K) and related resistors.
24. For Changhong C3419PS, a 5cm retrace line appears at the top. Check and replace C318 to resolve the issue.
25. Changhong R2518AE constantly burns the tube. Check C436 and C435RO. If they are blue CBB81 type, replace them. After replacing the capacitor and tube, everything works normally.
26. Changhong 2938FD has no sound. Check resistor 872 (0.27/0.5W) and replace it with a 1W/0.33 version to restore functionality.
27. Changhong R2519N automatically shuts down and sometimes won't boot. R820 (0.15 ohm) has deteriorated to 0.5 ohms or more. Replacing it fixes the issue.
28. For Changhong 2518FN series, the upper length is long, and the lower side is compressed. A 3–4 cm area has no light due to a faulty C306 (4700/25V).
29. Changhong R2519N (using TDA6103Q for viewing) has slightly brighter brightness due to R421 (100K) increasing. If the boot is too bright, open RX19 (220K).
30. Changhong D2962A has three no issues. The line has been worn, and C461 (7200P/1500V) is deteriorated. Replace it to restore normal operation.
31. Changhong G2536 fails to save the table and has a blue background. Fine-tuning allows saving. Check CPU pin 36 for C022–(101N). Normally, it should read 3.5–4.5V.
32. For Changhong T2981 and T2982, the map difference is caused by a faulty antenna input amplifier. Try swapping the tuner and antenna input box.
33. Changhong SF2915 has power indication but won't boot. Check CPU (N100) 3.3V voltage, which is only 2V. Replace V871 (C2688L) in the power supply to fix the issue.
34. Changhong 2588K burns the line. The new line-changing tube has low pressure. Check C472 (7200P/1600V) on the pillow board and replace it.
35. Changhong C2919PK runs some channels after a few minutes but fails to complete auto-search. Check the middle of the main box for a bad component.
36. Changhong C2919PS runs irregularly. Cracks on the main high-frequency head pin need re-soldering.
37. Changhong 2118FA burns V432 (D1651). After checking the power supply and capacitors, VD441 (RM11C) is found to be shorted in the deflection circuit.
38. Changhong G2125 has instructions but won't boot. Check for a short in the 18V power supply. V832 (D400-E) is faulty, causing D834, D835, and R824 to burn. Replace them to restore normal operation.
39. Changhong SF2551 has three no issues. Replace N801 (STR-F6454), VD830, VD808, and V801 (C2655) to resolve the issue.
40. Changhong C3419PD lacks Y signal. Check the clarity enhancement box and short-circuit pins 1–3 for emergency troubleshooting.
41. Changhong H29D80 has poor sound and only "black" sound. Z608 (L6.5C) is faulty. Replace it to fix the issue.
42. Changhong G2985 (B) has line distortion, with a 1CM difference left and right. Increase R931 (0.5W15 Europe) to 150 ohms and replace it.
43. Changhong C2152 (KV) uses LA7680 for small signals. It turns on after a few minutes. Replace C563 (35V/330UF) to fix the issue. If there's wood grain interference, check C562.
44. Changhong T2982 has power but won't boot. VD408 (RU4Z) is faulty. Replace it to restore normal operation.
45. Changhong C3419PD has normal standby but burns C4706 adjustment tube. The 400V/560UF capacitor is faulty. A "beep" sound accompanies the boot.
46. For Changhong C3419PK, the main power supply is 115V but only reads 100V. R868 (270K/1W) is open. Replace it to fix the issue.
47. For Changhong HP series rear projection power supply improvement, change R888/270K/1W to 470K/1W. Add a 0.22UF/250V capacitor between VC801 (2)-(3) feet to eliminate "zhi" sounds and interference.

Additional Notes:
1. When repairing A6 movement color TVs or fixing TDA7496 without sound, connect CRT, main speaker nets, and main board ground via screen wire.
2. For some models with snowflake points and noise, reduce the resistance of R115 (0.01UF) at the E pole of V101 in the front IF amplifier circuit.
3. For A6 movement color TVs with green screen after color saturation, check LA7688 (1) external components and LC89950. Measure the voltage of pin 1. If it's within 1.7–2.6V for TV-PAL/NTSC or 2.9–3.8V for AV-PAL/NTSC, the fault lies in LC89950 and surrounding circuits.
4. For A6 movement 21-inch TVs with frequency drift under program number "1", replace the original CPU with CHT0408-5L21. It can also replace CHT0405-5J77 and CH0403-5H61.
5. LA7688A can be replaced with LA7688B. To prevent multiple damage, add a soldered capacitor between R362 and VD622 on the Y board (board number JU7.820.1534/1360). On another Y board (JU7.820.1535/1462), add a capacitor between V617 "C" pole and the display tube base ground. Use CT-500V-100P.

Changhong 2
6. For CN-5 movement, if a map appears and there's a horizontal bright line, check AN5095 (20) foot for automatic brightness control circuit components. If the voltage is below 0.7V, the maintenance switch circuit is activated.
7. Use specified components for CN-5 switching power supply. For example, use THD215 for the switch.
8. Enter maintenance mode on CN-5 by shorting CPU (36) or (9) to ground. Press the background button on the remote to set machine parameters. FF-FF will appear on screen. Press repeatedly to select two parameters and adjust with volume button. See table for parameter values for various models.

Changhong 3
1. When replacing TEA2261 with BL8701 on NC-5 movement power supply, change from 1.5K to 6.8K and R818 from 680 ohm to 1.5k.
2. Later CN-5 products had power supply component changes: C821 changed from 0.68U to CD11-50V-1UF; C825 from 50V/1UF to 50V/2.2UF.
3. L801 without 1uH inductance can be replaced with 2.2uH.
4. Some CN-5 color TVs have a "wengweng" field. Change C675 from CD11-16V-470uf to CD288H-16V-2200uF.
5. Improve stability of CN-5 movement: Change R819 to RT13-0.166W-330 ohm; R822 to RT13-0.166W-1.3K; C821 to CD11-50V-1UF; C825 to CD11-50V-2.2UF; C824 to CL21X-50V-1000PF.

Changhong 4
1. CH-10 movement power supply C-MOS tube V840 can be replaced with STW10NB60, BUZZ334, IRFIB5N65A. Only shift VD840 and R821.
2. Four CPUs for CH-10 movement: CHT0808, CHT0818, CHT1201, CHT1202. CHT0808 and CHT0818 use 8MHZ crystals; others use 6MHZ. Don’t mix.
3. For CH-10 movement, boot time issues with flashing black screen and noise: Change R061 from 470 to 100 ohm; W076 from 2CK75D to hanging needle. For TDA6108 damage, increase RY04A, cut XPY03, and adjust VDY01A, VDY02A, VDY03A.
4. For character jitter, change BE pole of V438A to 5MM hanging needle; change R120 to CL21X-50V-6800PF.
5. For local station black screen, try changing CHT0808 to CHT0818 or adjust signal modulation to 87.5% and video sync amplitude to 30%. If not working, reduce R206.
6. BSC68H2 and BSC70E2 used in G2985 are interchangeable.
7. For V840 (W10NB60) and VD840 (WOSZ15B) damage, replace VD873 (RG2) with BYM26D to eliminate the issue.

Changhong 5
1. For karaoke signal issues on CN-12 movement TVs, connect two sets of diodes (each with three 2CK75D in series) to C523A "+" and R501. One set connects to C523A positive, the other to R501 ground. See diagram.
2. G2502 and G2911B color TVs with karaoke sound use method (3).

Changhong 6
1. For NC-6 movement, change R123 to 1K and C125 to 0.1UF.
2. For G2966B color TV data disorder and VGA loss, adjust OPT0 to 81 and OPT1 to 87.
3. For NC-6 movement power supply repair, discharge C810 with 10K resistors. If STR-S6709 is damaged, replace D809 and D815 (even if measurements are normal).
4. For G2967A with three faults due to sound amplifier block damage, replace the block and Z889, and check the clamp diode and speaker wires.
5. For sawtooth interference on NC-6 movement screen, replace L442 (TLN3063) due to poor performance.