Saturday, 15 January 2022

Sony KV-XA34M30A-RM-952 – South Africa – How to enter the service mode, service mode adjustments, LED blinking error codes, and schematic

 

SELF DIAGNOSTIC FUNCTION (LED blinking error codes)

The units in this manual contain a self-diagnostic function. If an error occurs, the STANDBY/TIMER lamp will automatically begin to flash.
The number of times the lamp flashes translates to a probable source of the problem. A definition of the STANDBY/ TIMER lamp flash indicators is listed in the instruction manual for the user’s knowledge and reference. If an error symptom cannot be reproduced, the remote commander can be used to review the failure occurrence data stored in memory to reveal past problems and how often these problems occur.
DIAGNOSTIC TEST INDICATORS
When an errors occurs, the STANDBY/TIMER lamp will flash a set number of times to indicate the possible cause of the problem. If there is more than one error, the lamp will identify the first of the problem areas.
Result for all of the following diagnostic items are displayed on screen. No error has occurred if the screen displays a “0”.

Note 1: If a + B over current is detected, stoppage of the vertical deflection is detected simultaneously.  The symptom that is diagnosed first by the microcontroller is displayed on the screen.
Note 2: Refer to screen (G2) Adjustment in section.

DISPLAY OF STANDBY/TIMER LIGHT FLASH COUNT

STOPPING THE STANDBY/TIMER FLASH
Turn off the power switch on the TV main unit or unplug the power cord from the outlet to stop the STANDBY/TIMER lamp from flashing.
SELF-DIAGNOSTIC SCREEN DISPLAY
For errors with symptoms such as “power sometimes shuts off” or “screen sometimes goes out” that cannot be confirmed, it is possible to bring up past occurances of failure for confirmation on the screen:
[To Bring Up Screen Test]
In standby mode, press buttons on the remote commander sequentially in rapid succession as shown below:
[Screen display] / channel [5] / Sound volume [-] / Power ON
˘
Note that this differs from entering the service mode (mode volume [+])

Self-Diagnosis screen display

HANDLING OF SELF-DIAGNOSTIC SCREEN DISPLAY
Since the diagnostic results displayed on the screen are not automatically cleared, always check the self-diagnostic screen during repairs. When you have completed the repairs, clear the result display to “0”.
Unless the result display is cleared to “0”, the self-diagnostic function will not be able to detect subsequent faults after completion of the repairs.
[Clearing the result display]
To clear the result display to “0”, press buttons on the remote commander sequentially as shown below when the diagnostic screen is being displayed.  Channel [8] / 0
[Quitting Self-diagnostic screen]
To quit the entire self-diagnostic screen, turn off the power switch on the remote commander or the main unit.

SELF-DIAGNOSTIC CIRCUIT

[+B over current OCP] Occurs when an over current on the +B(135) line is detected by Q604. If Q604 go to ON and the voltage to pin 18 of IC301 should go down when V.SYNC is more than seven verticals in a period, the unit will automatically turn off.

Vertical deflection stopped] Occurs when an absence of the vertical deflection pulse is detected by Q509 and IC001 shut down the power supply.
Vertical deflection over current] Occurs when an over current on V drive line is detected by Q507. Power supply will be shut down when detect this by IC001.
White balance failure] If the RGB levels* do not balance or become low level within 5 seconds, this error will be detected by IC301. TV will stay on, but there will be no picture.
* (Refers to the RGB levels of the AKB detection Ref pulse that detects IK.)

"RESET" FUNCTION
1. Purpose
If a customer faces some setting problem that cannot be solved, using the "RESET" function some items will be reset to its original setting (shipment condition)
2. How to Operate
The way to access to the "RESET" Function:-
a) By pressing "MENU" button or "SELECT" button (for non-menu models) on the Front Key Input and hold it down for 5 seconds.
3. Subsequent of Operation
Sequential to the resetting operation (either methods being used in No. 2), TV set would shut down once and automatically turn on again. The power-off duration is expected to be about 500msec. An OSD message, "RESET" tentatively will be displayed for 10 sec after IK status gets stable.
As a result, some items will be reset to an initial condition (shipment condition) whereas some other remains at the last selection by user.
Items that remains at the last selection by user
Reset Items
Program No., Favorite CH Setup, PIC rotation, OSD Language, Fine tuning, TV System, Skip.

FOCUS ADJUSTMENT
1) Receive digital monoscope pattern.
2) Set "AV CONTROL" to "DYNAMIC"
3) a) Adjust FOCUS VR so that centre of the screen becomes just focus.
4) Change the receiving signal to white pattern and blue back.
5) Confirm MAGENTA RING is not noticeable, Incase magenta is very obvious, adjust a FOCUS VR to take balance between MAGENTA RING and FOCUS.
FLYBACK TRANSFORMER (T503)
Screen
Focus
WHITE BALANCE ADJUSTMENT
1) Set to Service Mode. ADJUSTMENTS WITH COMMANDER
2) Input white raster signal.
3) Set the PICTURE to minimum.
4) Select GCT (WHB 4) and BCT (WHB 5) with [1] and [4], and adjust the level with [3] and [6] for the best white balance.
5) Set the PICTURE to maximum.
6) Select GDR (WHB 1) and BDR (WHB 2) with [1] and [4], and adjust the level with [3] and [6] for the best white balance.
7) Write into the memory by pressing [MUTING] then [0].
SUB BRIGHT ADJUSTMENT
1) Set to service mode.
2) Input a staircase signal of black to white from the pattern generator.
3) BRIGHTNESS .... 50%.
PICTURE ............MINIMUM
4) Select SBR (WHB7) with [1]and [4], and adjust SBR (WHB7) level with [3] and [6] so that the second stripe from the right is dimly lit.
G2 (SCREEN) AND WHITE BALANCE ADJUSTMENTS
G2 (SCREEN) ADJUSTMENT
1) Set the PICTURE to normal.
2) Put to VIDEO input mode without signals.
3) Connect R, G and B of the C6 board cathode to the oscilloscope.
4) Adjust BRIGHTNESS to obtain the cathode voltage to the value below.
5) Adjust G2 (screen) on the FBT until picture shows the point before cut off.

Service mode

ADJUSTMENTS WITH COMMANDER
Service adjustments to this model can be performed using the supplied Remote Commander RM-952.
a. ENTERING SERVICE MODE
With the unit on standby  press  Display > 5 > Volume (+) > Power.  This operation sequence puts the unit into service mode.

Service mode screen display

METHOD OF CANCELLATION FROM SERVICE MODE
Set the standby condition (Press [POWER] button on the commander), then press [POWER] button again, hereupon it becomes TV mode.
METHOD OF WRITE INTO MEMORY
1) Set to Service Mode.
2) Press [1] (UP) and [4] (DOWN), to select the adjustment.
4) Press [MUTING] button to indicate WRITE on the screen.
5) Press [0] button to write into memory.
MEMORY WRITE CONFIRMATION METHOD
1) After adjustment, pull out the plug from AC outlet, and then plug into AC outlet again.
2) Turn the power switch ON and set to Service Mode.
3) Call the adjusted items again to confirm adjustments were made.

ADJUSTMENT METHOD
Item Number 00 of device GEO
This explanation uses H-Position as an example.
1. Select “GEO 00 HPS” with the 1 and 4 buttons.
2. Raise/lower the data with the 3 and 6 buttons.
3. Select the optimum state. (The standard is 1F for PAL reception.)
4. Write with the [MUTING] button. (The display changes to WRITE.)
5. Execute the writing with the - button. (The WRITE display will be changed to red color while executing, and back to SERVICE.)



Use the same method for all Items. Use 1 and 4 to select the adjustment item, use 3 and 6 to adjust, write with [MUTING], then execute the write with -.
Note : 1. In [WRITE], the data for all items are written into memory together.
2. For adjustment items that have different standard data between 50Hz or 60Hz, be sure to use the respective input signal after adjustment.

PICTURE QUALITY ADJUSTMENTS - SUB COLOR ADJUSTMENT
1. Input a PAL color-bar.
2. Set to the following condition:
PICTURE 100%, BRIGHTNESS 50%, COLOR 50%
3. Connect an oscilloscope to pin1(B OUT) of CN305, A board.
4. Set to Service Mode and select SAJ 3 ‘SCL’ with 1 and 4 of the commander then adjust to VB2=VB3=VB4 with 3 and 6.
5. Press [MUTING] → - of the commander to write the data.
6. Adjust SAJ 3 ‘SCL’ as step 2 to 5 when receiving NTSC color-bar.

SUB HUE ADJUSTMENT
1. Select Video.
2. Input a NTSC, color-bar, into Video.
3. Set the following condition:
PICTURE 100%, BRIGHTNESS 50%, COLOR 50%
4. Connect an oscilloscope to pin 1 (B OUT) of CN305, A board.
5. Select SAJ 1 ‘SHU’ with 1 and 4 of the commander by setting to Service Mode and adjust to VB1=VB2=VB3=VB4 with 3 and 6.  The highest level of VB1,VB2,VB3,VB4 must be aligned at the same line. Ideal difference level between VB2 and VB3 should be within ± 110mV. 

6. Press [MUTING] → - of the commander to write the data.

DEFLECTION ADJUSTMENT
1. Set to Service Mode.
2. Input PAL color bar.
3. Using the 1 and 4 button, select category GEO (Service Mode).
4. Raise/lower the data using the 3 and 6 buttons.
Select and adjust the following items to obtain optimum image

5. Input 525/60Hz signal.
6. Using the 1 and 4 button select category GEO (Service Mode).
7. Select and adjust the following items to obtain optimum image. Raise/lower the data with the 3 and 6 buttons.


H-TRAPEZOID ADJUSTMENT
1. Receive cross hatch/dot signal.
2. Adjust RV1801 on C6 board to make H-trapezoid distortion best.

A BOARD ADJUSTMENT AFTER IC003
(MEMORY) REPLACEMENT
1. Enter to Service Mode.
2. Press commander buttons 5 and - (Data Initialize), and 2 and - (Data Copy) to initialize the data.
3. Call each item number and check if the respective screen shows the normal picture.
In cases where items are not well adjusted, rectify the items with fine adjustment.
Write the data per each item number ([MUTING] +-).
4. Select item numbers “OPB0” (OP1), “OPB1” (OP2), “OPB2” (OP3), “OPB3” (OP4) and respectively set the bit per model with command buttons 3 and 6.
5. Press commander buttons 8 and - (Test Normal) to return to the data that was set on the shipment from the factory.
(This will also cancel Service Mode.)

PICTURE DISTORTION ADJUSTMENT


Schematic diagram








Voltage list





Tuesday, 30 November 2021

Haier 40DR3505 LED TV-MSD3393LU Chassis – how to enter the service mode, how to disassemble, amplifier schematic

 

How to disassemble the TV

Remove the Stand

Remove the Back Cabinet

Remove the power-main board.

Remove the Speaker

How to remove the stand

1. Lay down the TV set .
2. Remove the four screws from the stand which in the picture.
3. Remove the stand.

Remove the Remote Control Board And the Key Board



How to remove the back cabinet.

1. Remove the fifteen screws indicated with red circles.
2. Flip machine, panel side up.
3.Carefully raise the Front shell from bottom.


How to remove the power-main board.

1. Remove the six screws indicated with red circles.
2. Then remove the side metal board and down metal board.
3. Remove the four screws indicated with red circles.
4. Remove the power-main board.

How to remove the speaker

Remove the speaker directly

How to remove the remote control board and the key board

Connectors definition

LVDS Interface connector

Amplifier schematic

How to enter into Service Mode
The way to the factory mode menu:
Step 1: Press Menu,
Step 2: Press “8893”,
System will be into the factory mode menu when 2 steps above are done.
At the end of the main factory menu, you can see the edition of the software, like this" BUILD TIME 2014-01-21 23:17:21 VERSION v1.0 ”.

How to exit
If you want to exit this factory menu, please press the button ”Exit” on the remote.
System will be out the factory mode menu.

In factory mode menu, press up/down button to choose the up/down item, press right or OK button to the submenu. Press MENU button to go back.

GENERAL SETTING
1)Init Flash;
2)Uart Enable: Choose on or off in Uart Enable;
3)Dbg Message Enable: Choose on or off in Dbg Message Enable;
4)Test Pattern: Choose the Pattern picture;
5)Dynamic Contrast: Choose on or off in Dynamic Contrast;
6)Power On Mode: Choose on or off in Power On Mode;
7)Mirror Control: Choose on or off in Mirror Control;
8)Front End Status
9)Timer Test
10)SSC
11)Erase Flash
12)PQ Advance Debug: Choose on or off in PQ Advance Debug;
13)Factory remote:
Open or close the
Factory remote;

Panel Setting
1)LVDS Bit Mode: choose the Bit;
2)LVDS MAP: choose the MAP;
3)LVDS ODD/Even: choose ODD or Even;
4)Bcaklight:Adiust the
value of backlight;
5)Reset Panel Setting Date
6)6MX0 LVDS Map:
choose the 6MX0 LVDS MAP;
7)
6MX0 Channel: choose the 6MX0 Channel;
8)6MX0 Mirror:
choose the 6MX0 Mirror;
9)6MX0 Demo:
choose the 6MX0 Demo;
10)6MX0 Update.

Main board

1. Mainchip—MSD3393LU(U1)
2. Audio Amplifier
—TPA3110D2PWPR (UA1)
3.Main Flash Memory—
GD25Q32BSIG (UF1)
4.DC/DC convertor 5V-1.8V for MSD3393LU (U1)—
LC1117CLTRAD (UL2)
5.voltage convertor 5V to 3.3V_STB —
LC1117CLTR33 (UL1)
6.voltage convertor 5V to 1.15V_STB —
LC3406CB5TR (UD1)
7.voltage convertor 5V to 3V for tuner—
LC1117CLTR33 (UT1)
8.Tuner —
SDCL1005CR33JTDF (RFT1)


Saturday, 9 October 2021

Akai 21CT32FSR CRT TV – service mode, adjustments, circuit diagram - TDA9381 and KASQ1265 as Power switching

 

Adjustment method

Main power +B setting
Receive standard color pattern RF signal, set picture to “ Standard Mode” . Adjust VR501. to get +B (VD631 -) voltage =110 V
I2C bus control adjustment method:
enter and exit factory mode
For remote controller of factory

Continuous push [test] key on  the remote controller, the TV mode will change as: Normal  è  M  è BUS OPEN

 You can select “M” ( factory mode ) or “normal” mode.

For remote controller of user
Push [menu] key,
→ display picture manual → push digital key 8500 → display M. Push [standby] key, exit factory mode and TV will be standby.

MENU 8 Geometrical adjustments.
Receive standard Crosshatch pattern signal for PAL system .
Horizontal line
Shadow
1) Adjust VSLOPE value
, to the horizontal line just appear from half bottom shadow.
2) Adjust VSHIFT value
, the centre horizontal line correspond to CRT vertical centre.
3) Adjust Vamp value
, to get 90% of vertical picture contents would be displayed on CRT.
4) Adjust HSHIFT value
, to get the picture horizontal centre correspond to CRT horizontal centre.
5) Receive standard Crosshatch pattern signal for NTSC system, and again adjust.

MENU 7 AGC-TOP adjustment
Receive 60dBu (1mv)VH colour bar signal, adjust AGC value(voltage from high to low), to picture noise reduce gradually to be just disappeared.

MENU 9 CRT cut-off and white balance and sub-brightness adjustment.
Receive gray and white 2 steps signal.
a) CRT cut off adjustment.
1. push [▲P+][▼P-] key to select “SC”, push [►V+][◄V-] key then automatically vertical scan will be stopped.
2. Adjust SCREEN control on Flyback transformer to get the darkest single horizontal line (red
、green, or blue, sometimes shows more yellow、more purple or more white).
3. Push [V+][V-] key again, vertical scan work repeat.

b) White balance adjustment.

1. Select RD/BD menu.
2. Adjustment RD/BD to get color temperature as x=281, y=311.
c) sub-brightness adjustment (use stair case signal)
1. Select SB MENU.
2. Adjust SB to get the darkest step being on or off.

MENU 6 Set SHIP MODE
Select “SHIPMODE”, push [V+][V-]key may be shipped.
Note:: may increase the screen of FBT current, the darkling single ought no fly back line, AV state.

I2C bus control adjustment item default setting (21 inch)


Note1:
TEXT DEF : TXT_def = 0: Pan_Euro + Cyrillic
= 1: Farsi English + French + Turkish
= 2: Arabic + English + French + Turkish
= 3: UKRAINIAN
Attention:
When TXT_def=0, will appear" the TXT LANGUAGE" in the customer Setup menu, press V+/ V- key," the TXT LANGUAGE" will appear the following circulation: W- TR-> EAST1-> EAST2-> W- TR
The W- TR diagram text includes the following language:
English German Swedish/Fin/Dan/Hungarian Italian French Spanish/Portuguese Turkish The EAST1 diagram text includes the following language:
Polish German Estonian Slovenian Czech/Slovak Rumanian
The EAST2 diagram text includes the following language:
Polish German Swedish/Fin/Dan/Hungarian Lettish Russian Slovenian Czech/Slovak Estonian
Note 2:
Make use of 4 color keys of the remote control, browse 4 pages of the enactment quickly, namely index function.
The TV/ AV sets the saving key for the index.
While using this function," the TXT LIST" establishes for" ON" in the customer menu.
Example: if want to use the color key of the red quickly 230 pages of enter the diagram text
The sequence press" TEXT"," red key","2","3","0" on the remote control," TV/ AV"
Note 3:
Switch on the hour appearance constitution
0: connect the AC power, enter to need the machine appearance automatically
1: connect the AC power, automatically switch on appearance
2: connect the AC power, if shut down the appearance as the diagram text appearance, enter the diagram text appearance automatically.

SCHEMATIC DIAGRAM

The main chips instruction. TDA93X1
The UOC (“Ultimate One Chip”) TDA93X1 is adopted in this chassis. This IC is the first available component that contains the complete control and small signal functionality needed for a TV application in one device.
The UOC TDA93X1 pins function description
:(total 64 pins)
Pin1: Standby control,“ 1” is on,“ 0” is off.
Pin2: SCL.
Pin3: SDA.
Pin4: Tuning PWM output.
Pin5: Auto AV control SW/NTSC SW,
Pin6: Key board input.
Pin7: Volume
Pin8: Mute control,
“ 1” is mute,“ 0” is off.
Pin9: Pin12
, Pin18, Pin30, Pin35, Pin41, Pin55: GND.
Pin10: BAND1 control output.
Pin11: BAND2
Pin12: GND
Pin13: SECAM PLL, connected with a capacitance.

Pin14: +8V power source supply.
Pin15: Using a capacitor of 220n in series to GND, This pin decouples the internal digital supply voltage of the video processor and minimizes the disturbance to the sensitive analogue parts.
Pin16: PHI-2 control loop, this pin requires a capacitor at 2.2nF (C) in series to GND.
Pin17: PHI-1 control loop, the loop filter connected to pin 17 is suitable for various signal conditions  strong/weak and VCR signal. This is achieved by switching of the loop filter time constant y changing the PHI-1 output current.
Pin18: GND.
Pin19: Band gap decoupling, the band gap circuit provides a very stable and temperature independent reference voltage. This reference voltage (4.0 V) ensures optimal performance of the analogue video processor part of the N301 and is used in almost all functional circuit blocks.
Pin20: East-west pillow signal output.
Pin21: Pin22
: Vertical drive output.
Pin23: Pin24
: IF input。
Pin25: Reference current, This pin requires a resistor to ground. The optimal reference current is 100mA which is determined by this resistor. The 100mA reference current should not be changed because the geometry processor is optimised for this current. Furthermore the output current of vertical drive and EW are proportional to this current.
Pin26: Vertical saw tooth, This pin requires a capacitor to ground of 100nF
Pin27: AGC output. This output is used to control (reduce) the tuner gain for strong RF signals.
Pin28: Audio de-emphasis.
Pin29: Sound decoupling. This pin requires a capacitor connected to ground. The pin acts as a low pass filter needed for the DC feedback loop.
Pin30: GND.
Pin31: Sound loop filter.
Pin32: AVL filter.
Pin33: Horizontal drive signal output, needs a resistor in series to +8V.
Pin34: Sandcastle output/fly back input,
Pin35: External audio input, this pin should be grounded in this chassis.
Pin36: EHT tracking/ overvoltage protection. If something is wrong, the anode high voltage rises, the heater voltage will rise too. When the rising voltage arrive some limit, the VD461 works, the voltage of pin 36 will exceed 3.9V, the N301will stop working.
Pin37: PLL loop filter.
Pin38: CVBS output. Monitor or RF videos can be selected.

Pin39: +8V supply source.
Pin40: CVBS input
Pin42: Y signal input.
Pin43: C signal input.
Pin44: Main audio output
Pin45: RGB signal input blanking.
Pin46, Pin47, Pin48: RGB signal input.
Pin49: ABL. It means been current limiter input. The R464 is the control resister.
Pin50: Black current input from the CRT board.
Pin51, Pin52, Pin53: RGB drive signal output to the CRT board.
Pin54: +3.3V.
Pin55: GND.
Pin56: +3.3V.
Pin57, Pin58, Pin59: 12MHz crystal
。
Pin60: Reset, NC in this chassis.
Pin61: +3.3V
Pin62: This pin is connected to the HEF4052, Functions expanding.
Pin63: This pin is connected to the HEF4052, Functions expanding.
Pin64: IR signal input.


Memory AT24C08 is an E2PROM of 8k, pins describe as follows:
Pin1, Pin2, Pin3,Pin4, Pin7: GND. Pin8: +5V supply.
Pin5: SDA. Pin6: SCL.


Wednesday, 29 September 2021

Rolsen RL 32D40D, Philips 715G6934P, GRADIENTE P1 Amp and RAG7 820.5338 Power board schematic

 

Philips 715G6934P01002002H [32 inch LCD TV SMPS] schematic



ROLSEN RL32D40D, RL32D40D, RL32D50D, RL32D60D - SMPS (Power board) schematic



RSAG7 820.5338 Power board schematic


Gradiente P1  Amp schematic



Monday, 20 September 2021

Toshiba 32A36C-service mode- full schematic diagram and waveforms

 

After turning the power off there might still be a potential voltage that is very dangerous. When removing the Anode Cap, make sure to discharge the Anode Cap's potential voltage.
Do not use pliers to loosen or tighten the Anode Cap terminal, this may cause the spring to be damaged.

Removal procedure of anode cap

Connect one end of an Alligator Clip to the metal part of a flat-blade screwdriver and the other end to ground.
While holding the plastic part of the insulated Screwdriver, touch the support of the Anode with the tip of the Screwdriver.
A cracking noise will be heard as the voltage is discharged.



SERVICE MODE – How to enter

This unit provided with the following SERVICE MODES so you can repair, examine and adjust easily.
To enter the Service Mode, press both set key and remote control key for more than 1 second.

CONFIRMATION OF HOURS USED
POWER ON total hours can be checked on the screen. Total hours are displayed in 16 system of notation.
NOTE: If you set a factory initialization, the total hours is reset to "0".

Set the VOLUME to minimum.
Press both VOL. DOWN button on the set and Channel button (6) on the remote control for more than 1 second.
After the confirmation of using hours, turn off the power.


WHEN REPLACING EEPROM (MEMORY) IC

If a service repair is undertaken where it has been required to change the MEMORY IC, the following steps should be taken to ensure correct data settings while making reference to TABLE

Enter DATA SET mode by setting VOLUME to minimum.
Press both VOL. DOWN button on the set and Channel button (6) on the remote control for more than 1 second.
ADDRESS and DATA should appear as FIG 1

ADDRESS is now selected and should "blink". Using the VOL. UP/DOWN button on the remote, step through the ADDRESS until required ADDRESS to be changed is reached.
Press ENTER to select DATA. When DATA is selected, it will "blink".
Again, step through the DATA using VOL. UP/DOWN button until required DATA value has been selected.
Pressing ENTER will take you back to ADDRESS for further selection if necessary.
Repeat steps 3 to 6 until all data has been checked.
When satisfied correct DATA has been entered, turn POWER off (return to STANDBY MODE) to finish DATA input.
After the data input, set to the initializing of shipping.
Turn POWER on.

Press both VOL. DOWN button on the set and Channel button (1) on the remote control for more than 1 second.
After the finishing of the initializing of shipping, the unit will turn off automatically.

The unit will now have the correct DATA for the new MEMORY IC.


Schematic diagram and printed circuit board



Microcontroller schematic diagram


Chroma section schematic

Deflection section schematic

Power [SMPS] schematic

Sound section schematic

Tuner section schematic

Audio-Video schematic

CRT socket section schematic

Comb filter schematic

AV jack schematic

Waveforms


Saturday, 18 September 2021

LG 52LG50FD, 52LG50FD-SA-Service adjustments-service mode entry-white balance adjustment-ADC component 1 RGB adjustment and more

  These adjustments are similar to 42LB7DF Because this is not a hot chassis, it is not necessary to use an isolation transformer. However...