1. For the Changhong LA7688N decoding block shutdown issue: remove VD611 and VD612 from the Y board, solder a 4148 diode back, connect VD613's positive to VD617-B pole.
2. The Changhong 29A18 model has incomplete line size; the main power supply is only 75–85V. After checking, VD520 is faulty, replace RU2.
3. For the Changhong CK56B2 (22") model, the field vibration occurs due to TA7698 integrated block 33 pin VCC + 8.6V dropping to about 4V. Check for open circuits in the push tube or transformer.
4. On the Changhong 2939FD, some stations show retrace lines entering the "S" bus and returning to ABK--ENABLE. Brightness increases during faults.
5. The Changhong N2918 TV shows a blue background with no picture on AV input. Adjusting AV fine-tuning brings sound, but the picture is unstable. Re-welding the comb circuit fixes the problem, likely due to leakage in capacitors. Note: Removing the button socket causes channel flipping.
6. On the Changhong C2589, black lines appear in the upper part. Linearity is poor. Replacing C329 (471K polyester) restores normal operation.
7. The Changhong C2191 emits a "zzz" sound and doesn't work. Unplugging the deflection coil shows normal line C voltage. C428 (1UF/250V) is shorted, so replacing it resolves the issue.
8. On the Changhong C2992, the upper image is jagged. Checking C825 (field supply capacitor, 35V/1000UF) shows it is normal.
9. The Changhong G2125 TV shows an upper half length issue. R402 (120K) is open, and replacing it fixes the problem.
10. The Changhong 2118FA (A6 movement) has VD514 (4148) open circuit. Main power is normal with a dummy load, but the tube burns after 2 seconds under load.
11. The Changhong C2919PK color TV has power indication, standby 50V is normal, but it protects immediately upon second boot. VD408 (RU4Z) is shorted, and replacement fixes the issue.
12. The Changhong G2132 (K) model has power indication but no secondary boot. No heating at the second boot. With a dummy load, the main voltage is 130V, but the deflection coil is shorted. This is a common failure.
13. The Changhong R2916N (R2518N same) shows line center shift right by 3 cm, no characters, AV also no picture. D403 and D404 (shorted) are replaced, with D404 (5.1V) restoring function. D403’s negative end should read 0.7V normally.
14. The Changhong 25K18 (LA7841 field block) shows upper compression, lower thinness. C301 (1000P) is bad, and replacing it fixes the issue.
15. The Changhong G29K36 shows bright horizontal line. N30 (LA7841) is faulty, and VD302 (1Z75) must be checked to avoid burning LA7841.
16. The Changhong 25N16 map shows 10cm compression and rolling. C302 and 10N capacitors are faulty.
17. The Changhong C2919PK (1) has upper retrace line, C318 (35V/220UF) is bad. (2) Upper retrace line without field, replace C305 (50V/1UF).
18. The Changhong C2919PS has stripes (not synchronized), and "black" sound (blue background off). Comb circuit is faulty.
19. The Changhong C2588A rare compression fault is resolved by replacing C317 (2.2UF).
20. The Changhong C2169 red "M" character fault indicates debug mode. If remote control cannot turn it off, press unused buttons between “SYS1/SRC†and “AN-SEL†to change color. If not fixed, replace the remote.
21. The Changhong C2169 and similar models start in AV state. This indicates program change, usually due to memory or external circuit issues. Replacement is needed.
22. The Changhong R2518AE (D) model has instructions but cannot turn on twice, with a "support" sound and burned tube. After checking, VD431 (1N4148) is defective in the push section.
23. The Changhong C2588PS has small upper retrace line. After checking, C320 is not faulty, but field blanking is bad. Replace R321 (2.2K) for troubleshooting.
24. The Changhong C3419PS has 5cm upper retrace line (normal amplitude). C318 is faulty, and replacement fixes the issue.
25. The Changhong R2518AE constantly burns tube. Check C436 and C435RO. If they are blue CBB81 type, replace them. After replacement, everything works normally.
26. The Changhong 2938FD has no sound. Check 872 (0.27/0.5W) resistor, which is open. Replace with 1W/0.33 to fix.
27. The Changhong R2519N automatically shuts down sometimes. R820 (0.15 ohm) deteriorated to 0.5 ohms, so replace it.
28. The Changhong 2518FN series shows upper length and lower compression, bottom 3–4 cm no light. Faulty C306 (4700/25V) is the cause.
29. The Changhong R2519N (TDA6103Q) has slightly brighter brightness due to R421 (100K) increasing. If boot is bright, open RX19 (220K).
30. The Changhong D2962A has three no-faults. The line is worn, and C461 (7200P/1500V) is deteriorated (including 5100P). Replace to fix.
31. The Changhong G2536 cannot save the table, and the blue background is off. Fine-tuning saves the channel. AV map flips. Check CPU 36th pin C022 (101N). Normally, 36th pin is 3.5–4.5V.
32. The Changhong T2981, T2982 has picture difference. Check the antenna input amplifier box and cross-line tuner and antenna input box.
33. The Changhong SF2915 has power indication but cannot boot. Check CPU (N100) 3.3V is only 2V. After replacing V871 (C2688L), everything is normal.
34. The Changhong 2588K burns line. New line has low pressure. Check C472 (7200P/1600V) on pillow board. Replace to fix.
35. The Changhong C2919PK starts after a few minutes, some channels run, but automatic search fails. Check middle of main box 1160 is bad.
36. The Changhong C2919PS runs irregularly (normal PIP). Cracks in the main high-frequency head pin need welding.
37. The Changhong 2118FA burns tube V432 (D1651). Power supply and capacitance are normal. Check VD441 (RM11C) in deflection circuit is shorted.
38. The Changhong G2125 has instructions but does not boot. Check 18V power supply has a short circuit. V832 (D400-E) is faulty, burn D834, D835, R824. Replace to fix.
39. The Changhong SF2551 has three no-faults. After replacing N801 (STR-F6454), VD830, VD808, V801 (C2655), everything is normal.
40. The Changhong C3419PD lacks Y signal. Check clarity enhancement box is faulty. Short-circuit 1–3 pins for emergency repair.
41. The Changhong H29D80 has poor sound, only "black" sound. Z608 (L6.5C) is faulty. Replace to fix.
42. The Changhong G2985 (B) has line width distortion, left and right difference 1CM. Change R931 (0.5W 15 ohms) to 150 ohms to fix.
43. The Changhong C2152 (KV): LA7680 small signal, has instructions, turns on after a few minutes. Replace C563 (35V/330UF) to fix. Wood grain interference can be solved with C562.
44. The Changhong T2982 has power indication but does not boot. VD408 (RU4Z) is faulty. Replace to fix.
45. The Changhong C3419PD has normal standby but burns C4706 adjustment tube. 400V/560UF capacitor is faulty. Booting produces a "click" sound.
46. The Changhong C3419PK has main power supply 115V only 100V. R868 270K/1W is open, causing volume issues.
47. The Changhong HP series rear projection power supply improvement: change R888/270K/1W to 470K/1W. Connect 0.22UF/250V capacitor between VC801 (2)(3) feet to reduce "zzz" sound and interference.
Other information: Changhong 1
1. When overhauling A6 movement 21" color TV failures, or when damaged due to TDA7496 failure, connect CRT, left and right speakers of main channel and main board to screen.
2. Some color TVs have more snowflake points in signal areas. Connect 0.01 UF capacitor across both ends of front intermediate frequency amplifier V101 E pole resistor R115.
3. A6 movement color TV displays black and white image normally, but after opening color saturation, full green screen failure. Check LA7688 (1) off-circuit circuit and LC89950 baseband delay processing block. Measure LA7688 (1) pin voltage. When TV receives TV-PAL/NTSC, this pin should be 1.7–2.6V. When operating AV-PAL/NTSC, this pin should be 2.9–3.8V. If (1) pin voltage is normal, fault is on LC89950 and surrounding circuits.
4. A6 movement 21" color TV has frequency drift under program number "1", but not under others. Solution: replace original CPU with CHT0408-5L21. CHT0408-5L21 can replace CHT0405-5J77 and CH0403-5H61.
5. LA7688A can be replaced by LA7688B. To avoid multiple damage to LA7688A, solder a capacitor between the left end of R362 and the positive end of VD622 on Y board JU7.820.1534/1360. On Y board JU7.820.1535/1462, solder a capacitor between V617 C pole and display tube base ground pin. Capacitor size: CT-500V-100P.
Changhong 2
6. CN-5 movement has map and horizontal bright line fault. Check AN5095 (20) foot external automatic brightness control circuit components. If (20) foot voltage is below 0.7V, maintenance switch circuit is activated.
7. Components used in CN-5 switching power supply must use machine-specified models. For example, switch must use THD215.
8. CN-5 movement enters maintenance method by short-circuiting CPU (36) to ground or CPU (9) to ground. After entering maintenance state, press background button on remote control to set whole machine function status. FF-FF will be displayed on screen. Press repeatedly to select two parameters, press volume button to adjust parameter size. Below is a list of parameter 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 movement power supply block is replaced by BL8701, the circuit changes from 1.5K to 6.8K; R818 changes from 680 ohm to 1.5k.
2. Later CN-5 movement products have changed power supply components: C821 changed from 0.68U to CD11-50V-1UF; C825 changed from 50V/1UF to 50V/2.2UF.
3. CN-5 movement power inductor L801 without 1uH inductance can be replaced with 2.2uH.
4. Some CN-5 movement color TVs have subwoofer "buzz": change C675 from CD11-16V-470uf to CD288H-16V-2200uF.
5. To improve stability and adaptability of CN-5 movement, the following improvements are suggested: R819 changed to RT13-0.166W-330 ohm; R822 changed to RT13-0.166W-1.3K; C821 changed to CD11-50V-1UF; C825 changed to CD11-50V-2.2UF; C824 changed to CL21X-50V-1000PF.
1. CPU: When CHT0807 is replaced with CHT0819, please disconnect D301.
2. To improve G2510B, G2529, G2532, G2536, G2538, G2539 and other color TVs, when receiving TV and AV signals, process the following circuits to solve problems. (1) Change flying wire (AWM1007-11/0.16 black 120MM) from W028 hole to W410 to AWM1007-11/0.16 black 70MM. Back weld to ground hole between original hole and W412 and R048. (2) Increase jumper W412 10mm. Note: Keep short wiring away from high frequency tuner and secure with tape.
Changhong 4
1. CH-10 movement power supply part C-MOS tube V840 can be replaced by STW10NB60, BUZZ334, IRFIB5N65A. Installation position only needs to shift VD840 and R821.
2. There are currently four CPUs for CH-10 movement: CHT0808, CHT0818, CHT1201, CHT1202. CH0808 and CH0818 use 8MHZ crystals; latter two use 6MHZ. Crystals must not be mixed, otherwise remote control won’t receive, but local buttons work normally.
3. CH-10 movement individual fault repair methods: (1) boot for period of time, screen appears gap black screen (flashing), accompanied by noise; sometimes after several flashes, automatically shut down (no B/B background), repeat above fault after booting. (2) Solution: Change R061 from 470 ohms to 100 ohms; W076 from 2CK75D to hang needles. (3) For some color TVs, TDA6108 is damaged multiple times. When full screen return line appears: A. Increase RY04A (0.5W/470 ohms), disconnect CY01 and CY02 printing line, install RY04A between CY01 end and CY02 positive end. B. Cut XPY03 (1) pin cable plug. C. VDY01A, VDY02A, VDY03A assembly method: keep three diodes’ positive ends unchanged, remove negative ends and connect to CY01 positive terminal. D. Increase hanging line at CY88.
4. Some color TVs have character jitter. When character shakes up and down for a while, (1) change BE pole of V438A to 5MM hanging needle; (2) change R120 to CL21X-50V-6800PF.
5. When receiving local station programs in some areas, instant black screen appears, sometimes blue background. Try changing CHT0808 to CHT0818 or coordinate local TV station to adjust signal to reach 87.5% national standard modulation, video signal sync head amplitude reaches 30% of signal amplitude. If above method doesn’t work, reduce R206 resistance.
6. Line change BSC68H2 and BSC70E2 used in G2985 are interchangeable.
7. When individual signal color TVs damage V840 (W10NB60), VD840 (WOSZ15B), VD873 (RG2), F801 (4A/250v), replace VD873 (RG2) with BYM26D to eliminate this phenomenon.
Changhong 5
1. When some karaoke signals are played in some types of color TVs produced by CN-12 movement, if sound is abnormal, connect grounding at C523A and R501, and connect two groups of diodes. Each set consists of three 2CK75D diodes in series. One set connects positive end of C523A to R501 ground, other set connects negative end of C523A to R501. See picture (2).
2. G2502 and G2911B color TVs produced by CN-12 movements have karaoke sounds, processed according to method (3).
Changhong 6
1. For individual channel in NC-6 movement, change R123 in main assembly to 1K and C125 to 0.1UF.
2. When G2966B color TV data is disordered and VGA function disappears, adjust OPT0 to 81 and OPT1 to 87.
3. When repairing NC-6 movement power supply, discharge C810 with 10K resistor. When STR-S6709 is damaged, replace D809 and D815 (note: replace even if measurements are normal).
4. When G2967A has three faults due to sound amplifier block damage, besides replacing sound amplifier block and Z889, check if clamp diode of power amplifier output block and speaker welding wire are too close.
5. Sawtooth interference in lower part of NC-6 movement screen: due to poor performance of L442, replace L442 (TLN3063) to fix.
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