Sansui g-5700 tuner bad

[ghazzer]

Here are some quick photos I took from my original SM. Bad lighting, but it reinforces what John said about the Sansui manuals being confusing when compared to actual PCA in hand.




This is the F-2980 (Left Drivers) from the G-6700 that may help. Ignore the F-3058 bd on the right. I have added in some of the numbered jumper pin holes. Some component values and components used may differ from the G-5700.

 

[Tomcow]

Anyone have an idea why I might be getting a high reading on one of the pre-drivers on a Sansui g-5700 receiver?Shouldnt the 4 pre-drivers be reading the same,.48-.51 diode setting as the 4 output transistors?

 

[Tomcow]

Now all is okay.Have to look elsewhere for the problem.

 

[Tomcow]

Well,I’ve checked about everything I can think of on this Sansui g-5700 board from hell F-2980.Im missing something somewhere but damn if I can find it.It powers on and dims my bulb dimmer right down but no relay on.Just sits there looking at me lit up but nothing!If anyone can give me some key points or things to recheck,I would appreciate any help to try and figure out what the problem might be.Thankyou!Tom.

 

[Hyperion]

What are the DC voltages like on pin 85 ------> to ground, and same for pin 86 ------> to ground (same pins you used for bias setting) - these are your DC offset readings - if either are above about 0.5V (or 500mV) the unit won't come out of protection.
Set your meter to say the '20V range' - and adjust down to get a reading if you can.

Obviously see if you can adjust the voltage found by adjusting the DC offset trimmers - one for each channel, adjust each trimmer to have the lowest possible voltage at those points - you are looking for 'mV' only.

Come back to us with voltage readings, or if you can't adjust.

 

[Tomcow]

Ok.So I got .56 volts(560mv) for pin 85 to ground and 4.5volts!!! For pin 86 to ground.Should I try adjusting the new Bourne trim pots I have in or is the problem way bigger than that?????

 

[Hyperion]

Ok.So I got .56 volts(560mv) for pin 85 to ground and 4.5volts!!! For pin 86 to ground.Should I try adjusting the new Bourne trim pots I have in or is the problem way bigger than that?????

No, go for it - just make sure your meter is 'looking' at the channel you are adjusting....

 

[Tomcow]

Ok.I got pin 85 to ground down to 0.0mv.pin 86 to ground I can’t get below 2 volts.

 

[Tomcow]

Any suggestions on where to look next?

 

[Hyperion]

Any suggestions on where to look next?

First try re-adjusting the bias.

 

[Tomcow]

The dc adjustment did bring it down from 4 volts to 2 volts but even a trimmer can only do so much.I have to keep hunting for a problem on that F-3980 board.Any more suggestions on test points would be greatly appreciated!!!

 

[Hyperion]

First try re-adjusting the bias.

The settings can and do interact - and as the DC offset was quite high on the side you had problems with, you should try re-adjusting the bias - and then try adjusting the DC offset on the 2 volt channel again. - it is a fairly slim chance but needs trying before proceeding.

 

[Tomcow]

Ok.Ill try that and get back to you.Thanks.

 

[Tomcow]

On the emitters of Tr05 and Tr07,I’m reading 35V on the bulb dimmer.On Tr06 and Tr08(high dc side)I’m only getting about 9V off the emitters.

 

[Hyperion]

On Tr06 and Tr08(high dc side)I’m only getting about 9V off the emitters.

Check R44 33Ω - might be damaged.

 

[Tomcow]

R44 measures 7.8K ohms

 

[Tomcow]

Tr15,pre-driver measures1.1V,emitter Tr17 measures .53mv,Tr-18 measures 1.8V,and Tr-16 measures2.1V .Only one of the 4 pre-drivers measures what I assume is the correct voltage from emitter to ground??

 

[Hyperion]

Tr15,pre-driver measures1.1V,emitter Tr17 measures .53mv,Tr-18 measures 1.8V,and Tr-16 measures2.1V .Only one of the 4 pre-drivers measures what I assume is the correct voltage from emitter to ground??

Don't worry too much with more voltage measurements for the time being that resistor should be 33Ω - and is actually 7.8KΩ ! - put that right and we'll see what happens.

 

[Tomcow]

Can’t believe I overlooked that I could hardly tell what color bands it had.Probably should replace with at least a 2 watt resistor?I appreciate the help you’re giving me,hope I can get it running!

 

[Hyperion]

Probably should replace with at least a 2 watt resistor?

No need to do that - ½ watt is fine, or even 1 watt.