Help please, Nsm century 21 (not prestige)

Hello my friend has a century 21 and the problem was when making a selection the carriage was just moving up and down a couple of times and not picking the record up.

So i guess the memory isn't getting written to or not been read.

So i changed all the capacitors for new ones on the main pcb, i also changed the thyristor and the bc transistor and fixed a few dry joints on the selection pcb the one with the buttons for selection.

Now what it does is it plays one record after the other, starting where the carriage is say 60 then it will play 59 then 58 and so on. it won't play the record that you select.

Anybody got any ideas? all the fuses are ok.

Thanks
Geoff



2 mal bearbeitet. Zuletzt am 19.08.13 22:14.

The pcb before i changed the capacitors.

Hello Geoff

You write that you have replaced the thyristor. Why have you changed it? Was it bad? Did you have an original thyristor or a replacement type? The BRY20 has special properties and a replacement type may not work properly.

Best regards - charly49

Hi charley it was a bry 39 that was fitted but marked on the pcb a 20 or a 39 can be fitted.
I don't know if it was bad but read a post they can fail.

I fitted a new bry 39.

Thanks
Geoff

Ps
I have schematics for the circuit boards.
And I used to work on video and tv repair 30 year ago,
But jukeboxes are new to me with all the mechanical parts of it.

So any help on where I should be looking is most welcome.

Thanks.
Geoff




2 mal bearbeitet. Zuletzt am 20.08.13 23:09.

Hello Geoff

If you have worked on TV and video equipment, you should have the necessary knowledge to find the fault.

I think the fault must be found at the thyristor or the surrounding components. The thyristor is responsible to operate the trip relay (LR) when a selection is found. In your case, the trip relay is obviously operated, even though no selection is found. A standard thyristor remains conductive after triggering as long as a holding current flows. The BRY20 is a so-called thyristor tetrode and works a little differently. It has a fourth port (anode gate) by which the thyristor can be turned off. This is done by grounding the anode-gate, as soon as the trip relay attracts. The thyristor should therefore always be just a short while conducting. You should check if the thyristor is actually switched off. It is also possible that he illegally fires when the voltage increases too quickly at the anode. This is an undesirable feature of this thyristor tetrodes.

The function of the circuit is also described in Service Manual accurately.

Best regards - charly49

Thanks again charly.

I'm abit rusty I did check all the components all the resistors where within tolerance.
Its all the relay action that's confusing.

On first selection say 50 pressing 5 I hear and see relays working then second digit 0 no relay noise.
The micro switch on the res button had dirty contacts now cleaned and working I have cleaned and checked the,
Contacts on all the other relays.

I will have another look at the pcb with the thyristor I may even put the old one back in.

Regards
Geoff

Another question is it possible all the memory could be written to without a selection been made?
If I unplug the connector from the memory the carriage moves up and down a couple of times then parks to the right.

I can't find any faults on the trip pcb.

Regards
Geoff

I even tried putting the original thyristor in.
I forgot to mention I'm getting 25v across the Zener I'm thinking that should be 27v

Geoff



1 mal bearbeitet. Zuletzt am 25.08.13 20:13.

Ok got the jukebox working duff capacitor and a couple of dry joints. Sound only coming from left side but not a problem for now but the volume controls look like they have been replaced sometime they not original. The volume is turned halfway before you get any sound.

Anybody know the ohm value of the original ?

Thanks
Geoff



1 mal bearbeitet. Zuletzt am 22.09.13 20:55.