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Marca del monitor	Modelo	Sintoma	Que hacer?
ACORN	28-AKF17 and 28-AKF30 14"	No display and whistling noise from PSU	Check Horz O/P transistor for S/C. If OK suspect EHT/LOPTX assembly. Test by substitution. A less common fault is a problem with the over voltage protection circuit. This is a crowbar type across the 28V supply and diodes 6452/6454 type PHF15 (15V 300mW Zeners) and thyristor 7452 type BT151 can fail causing a short circuit. These can fail for no apparent reason or a fault in the regulator circuit causing excessive voltage. If these have failed remove them from the circuit and disconnect the following. Collector of the horizontal output transistor to avoid the possibility of excessive EHT, R3563 feed to frame O/P and R3512 feed to horizontal drive circuits. Connect a meter across the 128V rail and switch on the unit. If the voltage is excessive and does not respond to adjustments with R3414 switch off immediately and examine the regulator circuitry. Transistor 3470 BC558B can also fail and is best tested out of circuit using a transistor tester. If in doubt replace it.
		No Horz drive but PSU working normally	Check R3512 28V feed to Horz drive circuit for O/C. (locate by following track from R3563 near front of board)
		Frame collapse just visible at max Brill	Check R3563 28V feed to Frame output circuit. (near front of PCB)
	AKF50 and Microvitec 1438	Dead	The following components can cause problems. IC1 = UC3844 8 pin PWM controller. TR1 FET BUZ80AFI. C8, D2 and D3, R20 2.2 Ohm and IC2 12V regulator. Another common failure is R6 15K going O/C. This is in series with R3 and appears to be mains sync feed to PWM chip IC1.
	AKF52 Microvitec Chassis	Intermittent tearing of vertical lines on screen	Several examples have had this fault. It is normally caused by poor joints on C18 in the PSU.
	AKF60 Microvitec Chassis	Power light comes on with no video input. If video is connected the power light flashes.	The video signal is switching the monitor out of power save mode and the flashing power light is caused by the PSU starting and shutting down due to an overload usually caused by a fault in the Horz O/P stage. Check the Horz output transistor BUH515D. If faulty and a replacement is not available a BU508DFI has been successfully used. NOTE:- On some examples of AKF60 substituting a BU508DFI can cause horizontal tearing for approximately 2 minutes after switch on. It is therefore recommended that a BUH515D is used. If this proves difficult to obtain it may be ordered from TANDY mail order department, or through a local store.
ARCH	514AS 14"	Very poor height and buzzing noise	The buzzing was coming from the scan assembly and L402 near the LOPTX was overheating. Cause was C406 0.68J capacitor O/C.
COMMODORE	1084 and 1084S	No display and faint whining noise	This problem is normally caused by the failure of the EHT/LOPTX unit. This is best confirmed by substitution.
	1084S-D1	No display and faint whining noise	Check D224 ERC06-15 flyback damper diode for S/C. If it has failed and this type is not available it may be substituted with a BY228 which is common in TV chassis.
	1084ST	No display and noise from PSU	Disconnect the collector of the line output transistor and check PSU voltages. If OK check the line O/P transistor for S/C. If transistor is OK suspect the LOPTX. This is normally a Sampo FEA188 which can be substituted with a HR transformer type number TFHR7495.
COMPAQ	460-P	Power light comes on then goes out	When power is applied the PSU starts up and then shuts down. Check the Horz output transistor for S/C. This example used a 2SC3482. This was replaced with a BU2508F and gave no problem during long soak test.
DAEWOO	Crystal 14S	No display or power light	If PSU appears to be working OK check Horz driver transistor 2SC3502-E for S/C. If this device is difficult to locate it can be replaced with 2SC2271 which is popular in many Televisions. After several minutes the display starts to jitter and the height and width reduces eventually resulting in complete loss of display. Suspect STR59041 IC in PSU circuit. This can often be confirmed by cooling the component with freezer to see if the fault clears for a few minutes.
ELONEX	CD1442VGA	Dead	Check voltage across smoother. If OK check R2 120K resistor on PSU board for high resistance or O/C.
	SV14LR 14"	PSU and EHT start up OK but no display	Check CRT heater supply circuit from PSU TX D818 cathode for +7.5 Volts. If voltage is low check C823 for low value/leakage. Should be 470uF but faulty unit measured 340uF on C tester.
		E.H.T fires up then shuts down and power light remains on	Common component failures on this chassis are C818, C820, C821, C424, C817, Q403 and R807. This particular symptom was caused by C424 33uF 160V capacitor located near the LOPTX.
	MN009/1 14"	No display or power light	If frame output and EHT appears to be working check for failure of the 7808 regulator mounted on the plate at the rear of the main PCB.
EMC	EF836 14"	Screen at Max Brill and displaying flyback lines	Check for approx. 90V across C230 47uF 160V on tube base PCB. If very low or 0V check R530 4R7 fusible resistor toward rear of main PCB for O/C.
ESCOM	ESCOM / HIT KT81-144C/8M	Low height and poor or no Horz sync	Using a CRO and X10 probe check for strong oscillation on 3.58MHz ceramic resonator X201 connected to IC201 near front of board. Approx. 40mV PtoP on one leg and 10mV PtoP on the other. If signal is missing or amplitude is poor replace the resonator.
GOLDSTAR	1460 14"	No Display	PSU was working but no EHT. No line drive due to no voltage on IC701. Fault D701 1N4001 diode near D711 high resistance.
HANTEREX	F1428SE 14" Could be TATUNG Chassis	Dead	Check voltage across smoother. If OK check R104 120K Resistor near the smoother for O/C.
ICPI	72G9140 14"	Dead	PSU not working but voltage across smoother OK. Check R603 and R604 33K 3W resistors in PSU for O/C.
MICROVITEC	Microvitec / Link / Commodore / Wyse LN15E 15" OSD	No Display or Power light	Check for faint ticking from PSU circuit. If so check Horz O/P transistor BU2520AF for leakage or S/C. If suspect replace with correct type. If after switching off the ticking noise gradually gets slower and dies away check Q603 2SC2655 in cold side of PSU circuit.
		Excessive width and pin cushion adjustment not working	Check D212 UF5408 soldered on heatsink near LOPTX.
	CUB (Metal Case)	Dead	If the mains input fuses are blown check the bridge recy for S/C and smoother C11 100uF or 220uF for leak or S/C. Failure of the PTC feeding the degauss coils can also cause the fuses to blow. A quick check can be made by simply disconnecting the degauss coil assembly. If the DC fuse F3 has failed check the chopper transistor for S/C.
		No display and the PSU can be heard tripping	The most common cause is excessive current being drawn by the Horz output stage. Check the EHT tripler/recy assembly by disconnecting it from the secondary of the Horz output TX. If the PSU runs normally replace the tripler assembly. Also check the Horz output transistor TR202 BU500 for S/C.
		Poor width and height or no display	Check HT rail on secondary of chopper TX i.e. across C26. If this voltage is low and the Horz output stage checks OK suspect one or more of the following in the PSU circuit. D18 BZX79 C7V5, D20 BZX79 C33V, TR1 BC307, C23 and C12 4u7 35V.
		Poor height or frame collapse	Most symptoms of this type are normally caused by the output chip IC301 TDA1170S.
MITAC	L1766PD 17" PC Monitor With OSD	Red Green or Blue video missing but colours OK while displaying built in menu screen.	Check the transistors type number 2SC945 on CRT PCB. Each transistor has a 68 Ohm resistor feeding the top leg. Check for approx. 1 volt at this junction of each device. If this voltage is incorrect suspect the relevant transistor.
		Intermittent loss of display and mode relay constantly switches on and off.	This was caused by a poor joint on inductor L906 in the PSU where the copper wire from the coil was wound round and soldered to the pin of the component not the PCB.
		Power and Aux. lights on EHT and PSU OK but no display	Increase A1 voltage to see if a display appears. If so try adjusting the Brill control. If this has no effect on Brill level check the following. Negative supply from anode of D509 near LOPTX. approx. -200V Voltages on Brill control connector J502 with control central. Black = 32V, RED = 43V, Yellow = 55V. All negative values. Check voltage swing on Brill control Red lead with control on Min (-55V) and Max (-32V) settings. If errors are found check the semiconductors in the ABL and associated circuits paying particular attention to Q525 2SC945 which can go leaky. This will normally only show if tested out of circuit.
	T1770HD 17" With OSD	Power light on but no display	The power light confirms voltage across the smoothers but check for expected voltage with a meter. If the voltage is OK check the feed resistors to the startup circuit R903 and R943 38K for O/C.
	1450PD 14" PC Monitor With OSD	1450PD 14" PC Monitor With OSD	Change Q201 2SC945 this should cure the problem. For improved reliability it is recommended that this device is substituted for 2SD669AC.
		Lack of width on early examples.	Change R907 1Meg for 1.5Meg 2W and R912 550 Ohm for 1K. Replace links JP950 and JP931 for 10 Ohm 0.25W resistors and remove C949. Check +B for 87Volts on loop near LOPTX. If necessary adjust with VR601 under CRT. Check for +145Volts on R924. If necessary adjust with ?
		No Display, but power and Aux. LEDs on and EHT OK	Slowly increase A1 control on EHT assembly and see if a display appears. If so adjust the Brill control. If it does not function check R507 56K resistor located near the Brill control connector for O/C. Adjust A1 back to correct level. Note: In some examples R507 is 33K. This will reduce the voltages on the Brill control by approx. 20V.
		Brill at Max and flyback lines are visible. Brill or Contrast have little effect	Check R505 100K near Brill control connector for O/C. Below are typical voltages on Brill and Contrast control connectors on a working chassis with controls at center. The feed to the Brill circuit is derived from the Horz output TX via D504 and smoothed by C511 10uF 250V. The voltage across C511 is normally 150V. Brill connector. Black = -50V, Orange = -65V, Yellow = -75V (see note above) Contrast connector. Yellow = +9V, White = +6V, Black = +2V
		Power light on but no display and AUX light not working	With video input signal connected check if a faint ticking noise can be heard from the PSU approx. twice a second. If so disconnect video signal and check if ticking stops. If it does check Q501 Horz O/P transistor on heat sink type BU2508DF for collector to emitter short. If this device is not available then use a substitute to verify fault cure. Types tested include BU2508D (not recommended as a permanent substitute as it will require an insulating kit) and 2SD1877. Both are popular in Televisions. When fault is confirmed it is recommended that the correct device is fitted.
		Power light on but no display	Check PSU, if it is not running check voltage across smoother. If OK check resistors R904 and R905 47K 2W for O/C.
	AM4050PD, similar to chassis 1450	Various	As this chassis is similar to the model 1450 many of the faults are common. The following is data that may be useful during fault finding. Any voltages were measured with a standard 20K OPV multimeter. Junction of D501 and D502 from pin 10 of LOPTX. 1000V AC or +50V DC. Anode of D502 65V AC or +9.4V DC. Anode of D504 from pin 4 of LOPTX neg 180V. Cathode of zener diode ZD502 to ground 25V. ZD601 160V, D609 90V, D914 95V, D915 160V, D918 95V, D919 25V, D920 7.2V U501 LM1391N Horz Osc Chip. Pin 1 = 0.75V 30uSec square wave 1to2 ratio 2V P to P. Pin 2 = 0V Pin 3 = 2V Inverse of 1 3.5V P to P. Pin 4 = 2V Poor sawtooth 1V P to P. Pin 5 = 3.2V Pin 6 = 9V Pin 7 = 4V Sawtooth 3.5V P to P. Pin 8 = 3.4V Clipped sawtooth 1.5V P to P. Q511 Line driver transistor Base 0.75V P to P Collector Square wave 30V P to P with 20V overshoot.
	L1564PDM 15" WITH OSD	Intermittent loss of picture and picture sometimes fades slowly.	This is typical of an intermittent heater supply fault. It is normally caused by poor soldered joints in the heater supply circuit. The supply is derived from D811 from the secondary of the chopper transformer and is supplied to the CRT base via an orange lead on a mutiway connector.
		Power light on but AUX light not working	Power light on but AUX light not working
MTC	EM1427 14"	Frame collapse and partial Horz scan	Check for supply voltage on frame chip IC301 TDA1170N. If OK in most cases the fault will be caused by failure of the IC. Note: If you have no data on this chip the schematics of early Microvitec monitors may aid fault diagnosis as they used the same device.
PEACOCK	PM14P48LR	Dead no display or power light	Check voltage on smoother. If OK PSU is probably not attempting to start. Check 27K resistors R603 and R604 for high resistance or O/C.
PHILIPS	4CM 4770/25T	Intermittent Horz Sync problems	May be connected with power save circuits. Try replacing link 3804 with a 100R resistor and changing transistors 7317 and 7320. All on tube base PCB.
	CM11342/CM11362/C M8832/33/52	No display and faint wining noise	Very common problem on these models see COMMODORE 1084 for details.
		Power light on but no display	Check 125V rail from PSU board. If this is low disconnect output power connector and check if voltage is OK. If so it is likely that the line O/P stage is drawing to much current. Check the output transistor for leaks, if all checks out disconnect the EHT cap from the CRT. If this results in a substantial increase in supply voltage suspect the Recy in the LOPTX assembly.
	7CM5279/20T	Power light on but no display	If PSU is working check for voltage on transistor 7512 (BC640). If voltages are missing suspect the transistor and resistor 3512 47R. Approximate voltages on a working unit are as follows. Base 90V, Collector 90V, Emitter 95V. In several units a 2N5401 has been used as a substitute but note the leadout is different.
SAMSUNG	CVM 4967T or Wearnes XGM-1415W 14"	No display but power light comes on	Check for 135V at adjust point near LOPTX. If voltage OK check L605 next to C614 for O/C. Should have approx. 25V on both ends. Colours on inductor RED, RED, BROWN, SILVER.
SAMTRON	SC-428PSL	Pale white background and text is green or other primary colour. A slight burning smell may also be noted	Check the 70V supply to CRT base PCB. If this is low it normally indicates that excessive current is being drawn by the video driver circuits. Any smell is usually caused by R600 70V feed resistor overheating on the main PCB and/or diodes overheating on the CRT base PCB. Check all the diodes on the tube base PCB they often suffer a high resistance reverse leakage, which does not always show on an ohm meter. If any diodes are suspect it is best to substitute them, or remove them and test for reverse leakage with a bench PSU set to around 30V. Connect the diode under test in series with a 1K resistor across the supply with the cathode to positive. If there is a voltage drop across the resistor, this indicates a reverse leakage and the diode should be replaced. The 1N4148 diode faults normally show on an ohm meter but the BAV21 diodes at locations D104R, D104B and D104G can have a reverse leak which will only show on a PSU test. These diodes have a 250V reverse voltage rating and must be replaced by a similar type. Voltages on the video output chip IC102 type LM2406T while displaying a DOS screen, starting from the top pin, are as follows. 72.2V, 2.7V, 72.2V, 2.9V, 71.8V, 74.4V, 0V, 1.4V, 1.4V, 11.6V, 1.4V. Also check for 72V across each BAV21 diode. We have had a few examples like this, the last had 6 duff diodes and a duff chip, this may have been caused by a flash over in the CRT.
TATUNG	3401 and AMSTRAD PC14M28LR/PC14M39	Works OK for a few minutes then shuts off	These symptoms are normally caused by the +B voltage rail drifting causing the EHT to increase and the overvoltage circuit to trip. Check resistor R504 220K in series with the +B adjust pot RV503. If the value is not correct replace with close tolerance high stab component.
		Powers up then the PSU shuts down and the power light goes out. EHT build up and collapse can also be heard which would normally indicate that the line output stage and EHT circuit main components are OK.	This symptom is common on this chassis and can be caused by a number of problems. If you have no service information then the following details should be useful. The shutdown of the PSU is often caused by triggering of the crowbar thyristor D418 across the 21V supply. This crowbar circuit monitors several conditions including EHT voltage. Excessive EHT is normally caused by a fault in the B+ voltage regulator circuit consisting of TR501 to TR505 and associated components. If the supply voltage is to high the EHT rises and trips the crowbar. EHT is monitored by a pulse taken from pin 3 of the LOPTX and is virtually instantaneous making diagnostics difficult. If the B+ regulator circuit is suspect a quick test can be carried out by disconnecting the emitter of TR504. As the circuit is a shunt regulator a supply voltage will be maintained Via the 150Ohm resistor R509. If the monitor runs check the following. The output/source voltage of the PSU which should measure 110V across C819 of the PSU circuit. The voltage drop across R509 which should be approx. 30V indicating that the Horz output stage is drawing the correct current. If all is well then it is most likely that the fault is in the regulator circuit. If the unit still shuts down, then as in most Horz output stages, failure of the tuning or damping components can also result in excessive EHT. Check D402, D403, C420 and C421. A problem with C420 is most common. When the unit is repaired adjust the B+ voltage at the emitter of TR504 to 84V with a Horz scan freq. of 31.5KHz using RV503. Some revisions of this unit incorporate a power saving circuit which removes power from the Horz output stage during the absence of video sync pulses. Failure of this circuit can result in similar symptoms to the above or no EHT at all due to no supply to the Horz output stage, but the power light remains on and the PSU runs normally. If fitted the circuit board is located on the heatsink near the LOPTX and is mounted with two screws. The circuit contains two distinct parts one incorporating IC701 74LS123 and the other transistors TR701/2 and Q701/2. If the circuit is suspect the fault can be quickly isolated to either section by moving the jumper PL704. If the monitor works then suspect IC701 and associated components or the wiring to the module resulting in the absence of sync pulses. If it does not work then suspect the section containing the transistors. It is unusual for a semiconductor to fail on this module and most faults are caused by faulty resistors particularly the higher values.
	TM5501	Power light on but no display	IF EHT etcetera are OK, check if CRT heaters are working. If not check supply (6.4V) from PSU board to power save control module. Two white wires from SK401 on PSU board Via ferrite ring to PL709. If voltage is missing suspect D828 on PSU board. If voltage OK check for broken joints on Q702 and PL908 on power save control PCB. If voltage is present on PL908 check for broken joints on tube base PCB.
TAXAN	SU775EV 14"	Intermittent loss of picture. Sometimes slowly fades while working	This is normally caused by broken soldered joints in the CRT heater circuit. Check Q906 and associated components (near front of main PCB). Also check C913 for intermittent O/C. If in doubt replace.
		No display and strange noises from area of PSU circuits	Many PSU problems are caused by the main input smoothers failing, causing excessive ripple. Remove them and test with a capacitance meter before proceeding with lengthy fault finding. Occasionally visible signs of leakage are apparent after they have been removed.
	SV787LR	Dead. Input fuse blown.	Before replacing the fuse check the following. The four diodes that form the input bridge and the chopper FET 2SK727. If the FET is S/C also check R825 0R39 ohm and D806 18V 500mW Zener diode. The failure of the FET can sometimes be cause by arking joints on the smoothing capacitor. Resolder these in all examples.
TRUST	CM2231 14"	Dead	Check fuse for O/C. If so make the usual basic cold checks for switch mode supply problems, but pay special attention to C821 560pF and D814 1N4936. In several examples of this model both these components have been S/C. Note: 1N4936 is a 1Amp fast recovery device.
TRUST		No display but power light showing green	PSU running OK. Poor line drive due to short circuit C415 104Z. This causes a high voltage drop across R431 resulting in low voltage to line driver stage. Voltage across C415 should be approx. 26V. Drive waveform to base of LOP transistor (across secondary of drive TX) should be approx. 2V PtoP.
TYSTAR	TY1415	No display and a whistling noise which dies away when switched off.	Check the Horz output transistor BU508A
WESCOM	GW500-E	Dead	This chassis has a separate power PCB which is often problematic. If the fuse is blown check the following. Bridge recy and Q3 2SC3460. If Q3 is S/C it may have also damaged the following. Q4 2SC1384, Q5 and Q6 2N2907A or 2N5401, IC3 4N35 Opto isolator and resistor R14 0.68 Ohm 3W. When this resistor was out of stock a 1 Ohm was used and operation appeared normal.</p> <p>Positive output voltage to Horz output stage is marked on PCB as 45-135V. During correct operation in a DOS screen +V = approx. 80V and +B = approx. 27V. With no video signal +V drops to approx. 53V.
WESCOM		Brill control not working	No negative voltage to Brill control due to R449 56K O/C. Also check negative voltage across C425 should be approx. 175V. The Brill and Contrast controls connect in a group of six wires near the edge of the PCB. The typical voltages on these wires are listed below working from left to right looking from the edge of the PCB. 1 = Min Contrast 2.5V, Max Contrast 10.3V 2 = 11V Small changes with Contrast & Brill 3 = Min Brill -14.3V, Max Brill +11.9V 4 = 12V 5 = 5V 6 = 0V Brill voltage on R450 Min -42V, Max -20.8V
UNBRANDED	15" Model SRC1502L	No display but power light shows orange and faint whine from PSU	Check Horz output transistor Q802 2SC3886A for short circuit. May be substituted with BU2508AF. If after replacing the PSU functions OK but the Horz output stage is dead check R422 1R5 resistor for O/C.
UNBRANDED		Display rotate intermittent	Check the trace rotate POT on the front panel. This should be a 1K high quality preset POT. On some examples this is 2K2 and the track suffers damage at the point where the wiper makes contact. The problem usually occurs the first time the pot is adjusted.