1. For the Changhong LA7688N decoding block shutdown issue, remove VD611 and VD612 from the Y board, and solder a 4148 diode in place. Connect VD613's positive to VD617-B pole.
2. Changhong 29A18 has incomplete line size. The main power supply is only 75–85V. After checking, VD520 is faulty. Replace RU2.
3. In the Changhong CK56B2 22-inch TV, the field vibration is abnormal. The TA7698 integrated circuit at pin 33 shows VCC + 8.6V, but it drops to around 4V. Check the line path, including the push tube and transformer.
4. In the Changhong 2939FD, the upper retrace line appears on some channels. Enter the "S" bus and return to ABK--ENABLE. When the fault occurs, brightness increases.
5. Changhong N2918 has a blue screen with no image when AV input is used. AV output has sound but no picture. Adjusting the AV fine-tuning brings sound, but the TV sometimes has sound with poor image quality. The Y signal seems lost. After repeated checks, the comb filter is faulty. Re-soldering fixes the issue. Note: Removing the button socket causes channel flipping.
6. Changhong C2589 has black lines on the upper part of the screen. Linearity is poor. After heating, C329 (471K polyester capacitor) is found bad and replaced.
7. Changhong C2191 makes a "zi" noise and doesn't work. Unplugging the deflection coil shows normal line voltage. C428 (1UF/250V) is shorted. Replacement fixes the problem.
8. Changhong C2992 has jagged upper image. C825 (field supply capacitor) is checked and found to be normal.
9. Changhong G2125 has an upper half length issue. R402 (120K resistor) is open. Replacing it restores normal operation.
10. Changhong 2118FA (A6 movement): VD514 (4148) is open. Main power is normal with a dummy load. The tube burns after 2 seconds when a load is applied.
11. Changhong C2919PK color TV has power indication and standby 50V, but fails during second boot. Line output load (pin 7) VD408 (RU4Z) is shorted. Replacement resolves the issue.
12. Changhong G2132 (K) has power indication but no secondary boot. No heating on the second boot. With a dummy load, 130V is normal. Investigation reveals a shorted deflection coil. This model is prone to this failure.
13. Changhong R2916N (R2518N same) has line center shift right by 3cm, no characters, AV also no picture. D403 and D404 (line pulse high voltage package pins 9) are shorted. Replacing D404 (5.1V) fixes the issue. D403's negative end should read 0.7V.
14. Changhong 25K18 (LA7841 field block) has upper image compression, lower thin. C301 (1000P) is bad. Replacement solves the problem.
15. Changhong G29K36 has bright horizontal line. N30 (LA7841) is faulty. Also check VD302 (1Z75) voltage regulator. If shorted, it may burn LA7841.
16. Changhong 25N16 has 10cm map compression and rolling. C302 and 10N capacitors are bad.
17. Changhong C2919PK (1) upper retrace line (no dark), replace C318 (35V/220UF). (2) Upper retrace line, no under field, replace C305 (50V/1UF).
18. Changhong C2919PS has stripes (not synchronized), black background, and sound issues. Comb circuit is faulty.
19. Changhong C2588A has rare compression failure. Replace C317 (2.2UF).
20. Changhong C2169 has red "M" character. This indicates entering debug mode. If remote control cannot turn off, press an unused button between “SYS1/SRC†and “AN-SEL†on K1L remote to make the red character turn green. If not resolved, replace the remote.
21. Changhong C2169 and similar models start in "AV" state. Indicates program change. Usually memory or external circuit failure. Replacing components resolves the issue.
22. Changhong R2518AE (D) has instructions but won’t boot twice. Tube burns. Check line frequency 15625, sometimes turns on but with left raster compression. After investigation, VD431 (1N4148) diode is faulty.
23. Changhong C2588PS has small retrace line. Not C320. Field blanking is bad (visual release). Check R321 (2.2K).
24. Changhong C3419PS has 5cm retrace line. Check C318, replace if faulty.
25. Changhong R2518AE constantly burns tube. Check C436, C435RO. If CBB81 type, replace. After replacing capacitor and tube, everything works.
26. Changhong 2938FD has no sound. No 16V. Check 872 (0.27/0.5W) resistor is open. Replace with 1W/0.33.
27. Changhong R2519N auto-shutdown. R820 (0.15 ohm) degrades to 0.5 ohms or more. Replace.
28. Changhong 2518FN series has upper length, lower compression, bottom 3–4cm no light. Caused by C306 (4700/25V).
29. Changhong R2519N (TDA6103Q) has slightly brighter brightness. ABL circuit R421 (100K) becomes larger. If boot is bright, open RX19 (220K).
30. Changhong D2962A has three no issues. Line worn, C461 (7200P/1500V) deteriorated (including 5100P). Replace.
31. Changhong G2536 search does not save table. Close blue background, fine-tune saves. AV map flips. Check CPU 36th foot C022 (101N). Normally 3.5–4.5V.
32. Changhong T2981, T2982 has picture difference. Check antenna input amplifier box. Cross-line tuner and antenna input box.
33. Changhong SF2915 has power indication but no boot. Check CPU (N100) 3.3V only 2V. Replace power supply V871 (C2688L).
34. Changhong 2588K burning line. New line has small line-changing tube (high pressure high). Check C472 (7200P/1600V) on pillow board. Replace.
35. Changhong C2919PK after a few minutes, some channels run, automatic search may not complete. Check main box middle week 1160 bad.
36. Changhong C2919PS irregular running (normal PIP). Crack weld at main high-frequency head pin.
37. Changhong 2118FA burning tube V432 (D1651). Power supply and capacitance normal. Check VD441 (RM11C) diode in deflection circuit.
38. Changhong G2125 has instructions, no boot. Check 18V power supply has short circuit. V832 (D400-E) bad, burn D834, D835, R824. Replace.
39. Changhong SF2551 three no. Replace N801 (STR-F6454), VD830, VD808, V801 (C2655).
40. Changhong C3419PD lacks Y signal. Check clarity enhancement box. Short 1–3 feet for emergency fix.
41. Changhong H29D80 has bad sound, only "black" sound. Z608 {L6.5C} bad. Replace.
42. Changhong G2985 (B), line width distortion, left/right difference 1CM. R931 (0.5W 15 ohms) increased to 150 ohms. Replace.
43. Changhong C2152 (KV): LA7680 small signal, with instructions, automatically turns on after several minutes. Replace C563 (35V/330UF). Wood grain interference with C562.
44. Changhong T2982 has power indication, no boot. VD408 (RU4Z) bad. Replace.
45. Changhong C3419PD has normal standby, starts burning C4706 adjustment tube. 400V/560UF capacitor bad. Boot accompanied by "click" sound.
46. Changhong C3419PK main power supply 115V only 100V. R868 270K/1W open.
47. Changhong HP series rear projection power supply improvement: R888/270K/1W changed to 470K/1W; VC801 (2)-(3) feet connected to 0.22UF/250V capacitor (power "zi" sound, interference (1) channel).
Other information: Changhong 1
1. During maintenance of A6 movement 21" color TV failures, especially after TDA7496 damage, connect CRT, left and right speakers of main channel and main board to screen.
2. Some color TVs have snowflake points in signal areas. Connect 0.01 UF capacitor across R115 (E pole) of front intermediate frequency amplifier V101.
3. A6 movement color TVs display normal black and white, but after color saturation opens, full screen green. Check LA7688 (1) off-circuit and baseband delay LC89950. Measure LA7688 (1) pin voltage. When TV receives TV-PAL/NTSC, it should be 1.7–2.6V. When AV-PAL/NTSC, 2.9–3.8V. If (1) pin is normal, fault is on LC89950 and surrounding circuits.
4. A6 movement 21" color TV has frequency drift under program number "1", no issue under others. Replace original CPU with CHT0408-5L21. CHT0408-5L21 replaces CHT0405-5J77 and CH0403-5H61.
5. LA7688A can be replaced with LA7688B. To avoid multiple damage, back-solder a capacitor between R362 left end and VD622 positive on Y board JU7.820.1534/1360. On JU7.820.1535/1462 Y board, back-solder between V617 "C" pole and display tube base ground. Capacitor size: CT-500V-100P.
Changhong 2
6. CN-5 movement has map then horizontal bright line. Check AN5095 (20) foot external automatic brightness control components. Voltage below 0.7V activates maintenance switch circuit.
7. CN-5 switching power supply components must use specified models. Example: switch must use THD215.
8. CN-5 movement enters maintenance by shorting CPU (36) or (9) to ground. Press background button on remote to set function status. FF-FF displayed. Press repeatedly to select two parameters, volume button changes parameter size. Table lists values for some models:
Item N2918 2916FN 2518FN 25N1, 29N16, 25N18, 29N18, 25N19 21〃 R2518N 2919FN Mode 1 27 07 07 04 C1 07 24 Mode 2 47 47 03 03 04 03 47
Changhong 3
1. When TEA2261 of NC-5 power supply block is replaced with BL8701, circuit changes from 1.5K to 6.8K. R818 changes 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 changed from 50V/1UF to 50V/2.2UF.
3. CN-5 movement L801 without 1uH inductance, can be replaced with 2.2uH.
4. Individual CN-5 color TVs have subwoofer "å—¡å—¡" field: change C675 from CD11-16V-470uf to CD288H-16V-2200uF.
5. Improve stability and adaptability of CN-5 movement: 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.
1. CPU: When CHT0807 replaced with CHT0819, disconnect D301.
2. Improve G2510B, G2529, G2532, G2536, G2538, G2539 color TVs: process following circuits to solve issues. (1) Change flying wire (AWM1007-11/0.16 black 120MM) to AWM1007-11/0.16 black 70MM. Back-weld between W028 hole and W410. Ground between original hole and W412 and R048. (2) Increase jumper W412 10mm. Keep short wiring away from high frequency tuner and secure with tape.
Changhong 4
1. CH-10 movement power supply C-MOS tube V840 can be replaced with STW10NB60, BUZZ334, IRFIB5N65A. Only need to shift VD840 and R821.
2. Four CPUs for CH-10 movement: CHT0808, CHT0818, CHT1201, CHT1202. CH0808 and CH0818 use 8MHZ crystals; latter two use 6MHZ. Cannot mix, otherwise remote control doesn’t receive, local buttons work.
3. CH-10 individual fault repair: (1) boot for period, screen appears gap black (flashing), noise, sometimes after flashes, auto shut down. (2) Solution: Change R061 from 470 ohms to 100 ohms; W076 from 2CK75D to hang needles. (3) Some color TVs TDA6108 damaged several times. Full screen return line: A. Increase RY04A (0.5W/470 ohms), disconnect CY01-CY02 printing line, install RY04A between CY01 end and CY02 positive. B. Cut XPY03 (1) pin cable plug. C. VDY01A, VDY02A, VDY03A assembly: positive ends unchanged, negative ends removed and connected to CY01 positive. D. Increase CY88 hanging line.
4. Some color TVs have character jitter. After time, (1) change V438A BE pole to 5MM hanging needle; (2) change R120 to CL21X-50V-6800PF.
5. Some areas have instant black screen when receiving local station programs, sometimes blue background. Try changing CHT0808 to CHT0818 or coordinate local TV station to adjust signal, reach 87.5% modulation, video sync head amplitude 30%. If not working, reduce R206.
6. Line change BSC68H2 and BSC70E2 used in G2985 are interchangeable.
7. When V840 (W10NB60), VD840 (WOSZ15B), VD873 (RG2), F801 (4A/250v) damaged, replace VD873 (RG2) with BYM26D.
Changhong 5
1. When karaoke signals played in CN-12 movement color TVs, sound abnormal. Use grounding at C523A and R501, connect two groups of diodes. Each set made of three 2CK75D in series. One set connected to C523A positive, other to R501 ground. See picture (2).
2. G2502 and G2911B color TVs have karaoke sounds processed according to method (3).
Changhong 6
1. For individual channel in NC-6 movement, change R123 to 1K and C125 to 0.1UF.
2. When G2966B color TV data disordered and VGA function disappears, set OPT0 to 81, OPT1 to 87.
3. When repairing NC-6 movement power supply, discharge C810 with 10K resistor. If STR-S6709 damaged, replace D809 and D815 (even if measurements normal).
4. When G2967A has three faults due to sound amplifier block damage, replace sound amplifier block and Z889, also check clamp diode of power amplifier output and speaker wire.
5. Sawtooth interference in lower part of NC-6 movement screen: due to poor L442 performance. Replace L442 (TLN3063).
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