CRT Vertical Fault - Sansui SV2960

[burntfingers]

Sansui SV2960

Partial vertical collapse.
Naturally, I looked for dry joints and replaced caps around IC - they were slightly lower.
No results.
Replaced vert chip - STV 8172A [brand new one]
Same shit!

I imagine it is some cap or a diode.
[I fear these faults, I really do!]
Have you had this one on this particular set - I have no service diagram.

[cadillacman]

Re: CRT Vertical Fault

recheck for cold solder at damn near every large resistor diode and heatsink mounted ic.

can you wiggle or tap the chassis and make this issue come and go or at least change?

[Toasty]

Re: CRT Vertical Fault

Don't curse in titles please. Public section of forums.



Manual at: http://elektrotanya.com/

.

[Krankshaft]

Re: CRT Vertical Fault

Check the supply voltage to the vertical IC is it normal?

If you don't have a service manual check the datasheet for the vertical IC to find it's normal supply voltage operating range.

Check the diodes with the diode check function around the deflection yoke connector as well.

[burntfingers]

Re: CRT Vertical Fault

recheck for cold solder at damn near every large resistor diode and heatsink mounted ic.

can you wiggle or tap the chassis and make this issue come and go or at least change?

I've wiggled the PCB to no effect.

Also checked other components for d/js.

[Krankshaft]

Re: CRT Vertical Fault

You're going to have to do some live measurements. Get the vertical IC datasheet to get the pinout and check the supply voltage.

[burntfingers]

Re: CRT Vertical Fault

You're going to have to do some live measurements. Get the vertical IC datasheet to get the pinout and check the supply voltage.

Just checked pin 2: reads 15 volts.
seems a bit low to me, for that big screen...?

Replaced the IC again, no luck.
Checked the supply smooth cap, it's OK.

[Krankshaft]

Re: CRT Vertical Fault

Is the pump up diode good it's the diode in circuit with the pump up capacitor? The diode is between the supply voltage and goes into pin 6 in the application circuit on the datasheet.

Do a voltage drop test on it with the diode checker function. It wouldn't hurt to heat it up or cool it down to see if it acts up either.

There is also a small cap from 47uf to 100uf which is part of the pump up circuit as well it's between pins 3 and 6.

Without this circuit functioning properly the beam can't snap back to the top of the screen. Usually issues like this result from a dried up pump up cap or bad pump up diode.

Beyond that check the vertical yoke dampening resistor it will either be on the PCB near the connector or soldered across where the wires solder onto the yoke windings. Check it for proper resistance.

I've attached the vertical IC datasheet for others interested.

Hopefully Wizard will chime in soon as well.

[burntfingers]

Re: CRT Vertical Fault

Downloaded diagram from Tanya, but it uses a different IC - TA8427K
Supply to IC is 28V.
My set reads 15.
I will check it again tomorrow.
This diagram shows a transistor Q451 in the supply.
Maybe it's the culprit - if there is one in the set.

[Krankshaft]

Re: CRT Vertical Fault

The datasheet said the IC can handle a supply voltage of up to 35 volts with a minimum being 10 volts.

C306 is the pump up cap and D301 is the pump up diode in that diagram.

[Longbow]

Re: CRT Vertical Fault

There is a cap on the cold end of the vertical yoke, typically 2200 uF or so. If that one is bad, it can cause this type of problem.

[Longbow]

Re: CRT Vertical Fault

Let me amend my previous statement. A large cap around 2200 uF couples the vertical signal to the yoke. At the cold end of the yoke there is a small value resistor used for current feedback to the vertical circuit. The coupling cap and the resistor are worth checking. The input to the vertical IC on pin 7 should be a believable linear ramp. As others have stated, a partial vertical raster is often caused by a bad pump up capacitor.

[burntfingers]

Re: CRT Vertical Fault

The datasheet said the IC can handle a supply voltage of up to 35 volts with a minimum being 10 volts.

C306 is the pump up cap and D301 is the pump up diode in that diagram.

D301 was it!

Why did I not replaced it, even though it measured ok?!...
When I gave it solder heat the picture opened up full screen.
Replaced it with a 1N4004 - it has been a while since I had trouble with such an item.

Thanks very much for the hint, Ks!
Much appreciated!

[Krankshaft]

Re: CRT Vertical Fault

Glad to help.

If the diode checker on the meter said it was ok it was probably failing under load.

The only way to make an intermittent semiconductor like this act up is with heat, cold, or by measuring the voltage drop with the circuit energized.

Congratulations you've fixed your first intermittent!

[burntfingers]

Re: CRT Vertical Fault

Glad to help.

If the diode checker on the meter said it was ok it was probably failing under load.

The only way to make an intermittent semiconductor like this act up is with heat, cold, or by measuring the voltage drop with the circuit energized.

Congratulations you've fixed your first intermittent!

Thanks.
Over the years - more than 30 - I've repaired MANY intermittent faults - and I still don't like them, the bastards! lol

[Krankshaft]

Re: CRT Vertical Fault

I've found it really tests your knowledge of the specific circuit failing. After you've isolated it to a certain circuit that is .

[lti]

Re: CRT Vertical Fault

Sansui CRTs seem to have lots if problems with the vertical deflection circuit. I have had two (one 27" and one 13") with bad pump-up caps.

[jacquesdejager]

Re: CRT Vertical Fault - Sansui SV2960

Hello --

I have a SV2960 that just switch on, and after +/- 3 seconds its switch off again - I assume this is the overvoltage protection circuit that get triggered.

I removed the 140V line from the HT side and connected a bulb to check the PSU, the PSU is stable and stayed on.

I assume it is some CAP / DIODE that is faulty in the HT side, any suggestions ?

Thank you