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Reparing dead Sansui TDC2075A

Harald Kapp

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Nov 17, 2011
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Welcome to EP.
These images are not much help. What we need to see are clear images of the power supply pcb - both top and bottom side.
Have you checked any fuses? Have you visually checked for suspicious components (burnt, swollen, leaked, exploded, ...) and for any visible bad solder joints?
Do you have a multimeter to measure resistance, voltages, currents?
 

MobiusOne

Jun 8, 2022
17
Joined
Jun 8, 2022
Messages
17
Welcome to EP.
These images are not much help. What we need to see are clear images of the power supply pcb - both top and bottom side.
Have you checked any fuses? Have you visually checked for suspicious components (burnt, swollen, leaked, exploded, ...) and for any visible bad solder joints?
Do you have a multimeter to measure resistance, voltages, currents?

I own a digital meter but I'm not 100% sure how I should be testing the caps resistors
I included more detailed images of the PCB of the main board with power cable and the flyback and that I know of there's only one glass fuse which I checked to be fine
https://imgur.com/gallery/CI1QHTp
 

73's de Edd

Aug 21, 2015
3,658
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Aug 21, 2015
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3,658
Sir MobiusOne . . . . .
( Now . . . . let's just see if we can get you all caught up in a Mobius Loop. )
With what I can JUST see / fathom from that supplied photo.
The NON blowing of that fuse is GOOD.
Its power supply circuitry may have just got "weak and lazy" from time of use.
If being yours from day one . . . and not a curb find ! ! ! . . . .how old is it being now ?
I am finding minus ZERO, freebie . . . . . schematic / tech svc manuals on this Sansui.

CIRCUIT ANALYSIS . . . .

AC Power comes in as the GREEN line and passes thru glass fuse and then into a few EMI filtering components and then into 4 power diodes which then have DC voltage coming out as the now RED line and it goes into a WHITE BLOCK 1.2 ohm line surge resistor.
That resistors other end goes into the MAIN filter cap as its + lead as the large black cylinder at far corner end chassis.
And then that voltage might ? pass to the RED STAR resistor and then out of it, YOU can confirm by examining its connecting foil path .
Then that supply voltage passes into a primary winding of the power transformer . . . at the end of that RED line.
The end of that primary winding comes out as the ORANGE line and then goes to a power switching transistor / or / FET at the end of the ORANGE line.
Pulses of variable frequency / and / or / widths drive that power transistor and it in turn drives the power transformer primary . . . . the sampling of one winding of the transformer secondary, feedback, and how it relates to power consumption changes, such that pulse changes fed to that power device . . . . . will hold all to an appropriate, regulated level.
The YELLOW ARROW output arrow is for the power transformers multiple secondary windings which will be rectified by the RED DOT diodes to then feed lower voltage DC to their companion filter caps . . as they, being the ones RED STARRED in the YELLOW BOXED area.

Sound KLAXXON horn . . . three LONG and LOUD bursts . . . . to alert for testing . . . . .


MARK UP . . . . . . . of . . . . . . TECHNO REFERENCING . . . . .
Sansui-20-in-TV-VCR-Combo-Board.png




HOWTOMAKEEANDDOTESTEE-TESTEE

First lets just see if that just described power supply is working . . . . since its tasked / committed for 24 hrs a day operation.
If the AC line plug is plugged in, its supposed to be working.
Take meter in hand and set up to read DC voltage, and I would expect the anticipated voltage range to be at a max of 50 VDC. .
If yours is being auto ranging . . .it does that adjustment aspect for you.

TESTING POINTS . . . .

Note the tuner housing that my BLACK . . . . . CIRCLE-STAR is identifying.
That would be a good COLD ground reference to stab your BLACK lead meter probe into / or a clip lead into.
Extreme top left corner, inside of the YELLOW rectangle, is a hefty diode . .RED dotted . . . and I expect its SILVER band end is
being one hefty current supply of voltage output .
Actually, it may have a like companion diode assisting it, as the diode being just below it.
Possibly, with that supply then feeding to the largest E-Caps located over to the right .
Alternate OTHER derived supply's could be the silver band end of the bottom left bottom corners diode.
Also the encircled by capacitors diode, located at the 2 o clock position from the MISSING E-capacitor on the board.
(Matter of fact, I believe that I can also see a SECOND like diode, being just above that one, include the testing of its silver band also.)
Probe those silver banded diode ends for any voltage presence / output.

S O O O O O . . . . . if you can get that all harnessed and plugged into its original operational condition, you can use those test points referenced , to see if you are getting any power supply activity after AC power plug insertion..
If not, we then see if the PRINCIPAL LARGE BLACK E-capacitor in the extreme top corner is getting its 160-170 'ish volts of DC power . . . . .( I sort of expect so)

Standing by . . . and jes' doin' my thang . . . . . .
EatingPopcorn.jpg


73's de Edd . . . . . .

Now, I may not be totally perfect . . . . . but, there are certain parts of me that are being absolutely superb.


.


.
 
Last edited:

MobiusOne

Jun 8, 2022
17
Joined
Jun 8, 2022
Messages
17
Sir MobiusOne . . . . .
( Now . . . . let's just see if we can get you all caught up in a Mobius Loop. )
With what I can JUST see / fathom from that supplied photo.
The NON blowing of that fuse is GOOD.
Its power supply circuitry may have just got "weak and lazy" from time of use.
If being yours from day one . . . and not a curb find ! ! ! . . . .how old is it being now ?
I am finding minus ZERO, freebie . . . . . schematic / tech svc manuals on this Sansui.

CIRCUIT ANALYSIS . . . .

AC Power comes in as the GREEN line and passes thru glass fuse and then into a few EMI filtering components and then into 4 power diodes which then have DC voltage coming out as the now RED line and it goes into a WHITE BLOCK 1.2 ohm line surge resistor.
That resistors other end goes into the MAIN filter cap as its + lead as the large black cylinder at far corner end chassis.
And then that voltage might ? pass to the RED STAR resistor and then out of it, YOU can confirm by examining its connecting foil path .
Then that supply voltage passes into a primary winding of the power transformer . . . at the end of that RED line.
The end of that primary winding comes out as the ORANGE line and then goes to a power switching transistor / or / FET at the end of the ORANGE line.
Pulses of variable frequency / and / or / widths drive that power transistor and it in turn drives the power transformer primary . . . . the sampling of one winding of the transformer secondary, feedback, and how it relates to power consumption changes, such that pulse changes fed to that power device . . . . . will hold all to an appropriate, regulated level.
The YELLOW ARROW output arrow is for the power transformers multiple secondary windings which will be rectified by the RED DOT diodes to then feed lower voltage DC to their companion filter caps . . as they, being the ones RED STARRED in the YELLOW BOXED area.

Sound KLAXXON horn . . . three LONG and LOUD bursts . . . . to alert for testing . . . . .


MARK UP . . . . . . . of . . . . . . TECHNO REFERENCING . . . . .
Sansui-20-in-TV-VCR-Combo-Board.png




HOWTOMAKEEANDDOTESTEE-TESTEE

First lets just see if that just described power supply is working . . . . since its tasked / committed for 24 hrs a day operation.
If the AC line plug is plugged in, its supposed to be working.
Take meter in hand and set up to read DC voltage, and I would expect the anticipated voltage range to be at a max of 50 VDC. .
If yours is being auto ranging . . .it does that adjustment aspect for you.

TESTING POINTS . . . .

Note the tuner housing that my BLACK . . . . . CIRCLE-STAR is identifying.
That would be a good COLD ground reference to stab your BLACK lead meter probe into / or a clip lead into.
Extreme top left corner, inside of the YELLOW rectangle, is a hefty diode . .RED dotted . . . and I expect its SILVER band end is
being one hefty current supply of voltage output .
Actually, it may have a like companion diode assisting it, as the diode being just below it.
Possibly, with that supply then feeding to the largest E-Caps located over to the right .
Alternate OTHER derived supply's could be the silver band end of the bottom left bottom corners diode.
Also the encircled by capacitors diode, located at the 2 o clock position from the MISSING E-capacitor on the board.
(Matter of fact, I believe that I can also see a SECOND like diode, being just above that one, include the testing of its silver band also.)
Probe those silver banded diode ends for any voltage presence / output.

S O O O O O . . . . . if you can get that all harnessed and plugged into its original operational condition, you can use those test points referenced , to see if you are getting any power supply activity after AC power plug insertion..
If not, we then see if the PRINCIPAL LARGE BLACK E-capacitor in the extreme top corner is getting its 160-170 'ish volts of DC power . . . . .( I sort of expect so)

Standing by . . . and jes' doin' my thang . . . . . .
EatingPopcorn.jpg


73's de Edd . . . . . .

Now, I may not be totally perfect . . . . . but, there are certain parts of me that are being absolutely superb.


.


.
Forgive me for being slow and having a late response but I REALLY appreciate your research into this and the detail.
I just want to be sure here... I should reassemble the TV set and test the voltage coming out of the power supply shown with the yellow arrow, and the likely culprits are the capacitors marked with a red star or the large one at the corner?

Just wanna be sure before I put stuff back together so I can go buy the correct parts I need and safely test the right thing.
While I don't know if this info help... I used an electrical tester pen (those that tell you something have live power running through it without making contact) and it DID go off past the marked areas so I do believe power is flowing that way but I did not use my multimeter at the time since I did not know what to probe and didn't want to have an accident
 

MobiusOne

Jun 8, 2022
17
Joined
Jun 8, 2022
Messages
17
Sir MobiusOne . . . . .
( Now . . . . let's just see if we can get you all caught up in a Mobius Loop. )
With what I can JUST see / fathom from that supplied photo.
The NON blowing of that fuse is GOOD.
Its power supply circuitry may have just got "weak and lazy" from time of use.
If being yours from day one . . . and not a curb find ! ! ! . . . .how old is it being now ?
I am finding minus ZERO, freebie . . . . . schematic / tech svc manuals on this Sansui.

CIRCUIT ANALYSIS . . . .

AC Power comes in as the GREEN line and passes thru glass fuse and then into a few EMI filtering components and then into 4 power diodes which then have DC voltage coming out as the now RED line and it goes into a WHITE BLOCK 1.2 ohm line surge resistor.
That resistors other end goes into the MAIN filter cap as its + lead as the large black cylinder at far corner end chassis.
And then that voltage might ? pass to the RED STAR resistor and then out of it, YOU can confirm by examining its connecting foil path .
Then that supply voltage passes into a primary winding of the power transformer . . . at the end of that RED line.
The end of that primary winding comes out as the ORANGE line and then goes to a power switching transistor / or / FET at the end of the ORANGE line.
Pulses of variable frequency / and / or / widths drive that power transistor and it in turn drives the power transformer primary . . . . the sampling of one winding of the transformer secondary, feedback, and how it relates to power consumption changes, such that pulse changes fed to that power device . . . . . will hold all to an appropriate, regulated level.
The YELLOW ARROW output arrow is for the power transformers multiple secondary windings which will be rectified by the RED DOT diodes to then feed lower voltage DC to their companion filter caps . . as they, being the ones RED STARRED in the YELLOW BOXED area.

Sound KLAXXON horn . . . three LONG and LOUD bursts . . . . to alert for testing . . . . .


MARK UP . . . . . . . of . . . . . . TECHNO REFERENCING . . . . .
Sansui-20-in-TV-VCR-Combo-Board.png




HOWTOMAKEEANDDOTESTEE-TESTEE

First lets just see if that just described power supply is working . . . . since its tasked / committed for 24 hrs a day operation.
If the AC line plug is plugged in, its supposed to be working.
Take meter in hand and set up to read DC voltage, and I would expect the anticipated voltage range to be at a max of 50 VDC. .
If yours is being auto ranging . . .it does that adjustment aspect for you.

TESTING POINTS . . . .

Note the tuner housing that my BLACK . . . . . CIRCLE-STAR is identifying.
That would be a good COLD ground reference to stab your BLACK lead meter probe into / or a clip lead into.
Extreme top left corner, inside of the YELLOW rectangle, is a hefty diode . .RED dotted . . . and I expect its SILVER band end is
being one hefty current supply of voltage output .
Actually, it may have a like companion diode assisting it, as the diode being just below it.
Possibly, with that supply then feeding to the largest E-Caps located over to the right .
Alternate OTHER derived supply's could be the silver band end of the bottom left bottom corners diode.
Also the encircled by capacitors diode, located at the 2 o clock position from the MISSING E-capacitor on the board.
(Matter of fact, I believe that I can also see a SECOND like diode, being just above that one, include the testing of its silver band also.)
Probe those silver banded diode ends for any voltage presence / output.

S O O O O O . . . . . if you can get that all harnessed and plugged into its original operational condition, you can use those test points referenced , to see if you are getting any power supply activity after AC power plug insertion..
If not, we then see if the PRINCIPAL LARGE BLACK E-capacitor in the extreme top corner is getting its 160-170 'ish volts of DC power . . . . .( I sort of expect so)

Standing by . . . and jes' doin' my thang . . . . . .
EatingPopcorn.jpg


73's de Edd . . . . . .

Now, I may not be totally perfect . . . . . but, there are certain parts of me that are being absolutely superb.


.


.
UPDATE TWO
Did the testing like you said and in the areas probed https://imgur.com/gallery/KJ8NtZO it read -62 and 62 depending on the spot and the part you marked with a yellow arrow coming out from and the box read ZERO.

Note again my hand slipped and I blew that resistor but I had done the testing before I blew it and took the images and the results were the same with it working and blown.

Also here's a better image of the caps if it helps https://imgur.com/gallery/IKBX6Um
 

MobiusOne

Jun 8, 2022
17
Joined
Jun 8, 2022
Messages
17
(bump and update)
Finally got them in and replaced the bad resistor on the Sansui board but still no power coming out of the switch-mode transformer
 
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