DAC90a - Not working??

[Shaman]

Hi Rob, looks as if you MAY have a faulty output transformer, to earth, this would cause the resistor across the cap,s Smoothing, to overheat and eventually burn. A replacement loud speaker transformer will eliminate this, it was fine till you put the feed from the transformer onto the capacitor, also check the tone cap across the transformer i think its C19 THIS SHEET 0.01uf....regards....Alan.

[Bushbaby]

Hi Alan,
I've a spare chassis from another DAC90a with a badly damaged ivory case. I am tempted to transplant the transformer from this to my other chassis.

Am I correct that i can test the 'faulty' transformer by passing a small current through the input side and connect the output side to a scope?

Regards

Rob

[Shaman]

Rob will ring you later....regards....Alan.

[Bushbaby]

Hi All,
After a few rechecks and amendments!! (one the things I discovered that the lead from R16 was attached to the 250v side of R17 - I changed this to the 230v side) the radio is working.

Lots of smoke from the mains dropper (R17) as this does appear to be quite new (thanks Rob T).

However, I noted that the dial lights were not working yet the set was?? These were 3.5v 200ma lamps instead of 150ma lamps. I swapped some lamps from another DAC90a which had 12v 0.1amp bulbs in it and these lit up albeit like cigarette ends - very dim! Is ther anything I can do to use the 3.5v 200ma lamps?

Thanks

Rob

[Joe]

Are you sure that BOTH the 3.5v ones work as if one is blown it will stop the other from lighting up.

Glad you've got it sorted at last.

Cheers

Joe

[Bushbaby]

Hi Jamie/Joe,
I'm led to beleive that its the current not the voltage that import with the dial lamps in these sets. There is not enough current to light the bulbs that I have in parallel (I've tested these seperately and they do work).
I'm not sure about changing the value of R16 as I don't how what effect this may have on the rectifier (V5)?

Regards

Rob

[tiv48]

i use 3.15 volt 200ma they work but not as bright as i would like
rob t

[Bushbaby]

Hi Rob,
If I put these in, they complete the heater chain so that the radio works but they do not light at all - any thoughts?

Regards

Rob

[Yorkie]

Hi Rob,
If I put these in, they complete the heater chain so that the radio works but they do not light at all - any thoughts?

Regards

Rob

The bulbs don't actually 'complete the heater chain', to the extent that if they fail, the shunt resistor (which takes part of the current to the heaters anyway) ensures continuity of the heater chain. One professional restorers fits a small 6V transformer just to power the bulbs. That way, you can use easily obtainable 6V bulbs which stay bright all the time the set is switched on. It can easily be removed later if desired, and I guess it depends on whther one places functionalty above originality. Others have fitted hi brightness LEDs with a series limting resistor, in old bulb bases.

Hope that helps.


David

[Aerodyne]

I've never yet seen a DAC90A with bright scale lamps. My conclusion is that the set was designed that way. 0.15A bulbs are correct, of course.
-Tony