Ampeg BA-115 HP Tweeter Issue

[exspes]

Hey Guys,

So the tweeter in my amp blew quite a long time ago, i got a new one today. While i had the amp out i took out the amplifier section and adjusted the bias trim pot so there was 17.6mV dropped across the resistors 72-75 as specified in the service manual, i did this because there was a lot of hum coming from the woofer even with the tweeter disconnected. Turned on the amp to check the hum and it was noticeably reduced (yey!). Turned off, reconnected the tweeter, turned on, i hear a slight hum coming from the tweeter and the woofer (nothing crazy, acceptable electrical noise). Plug in my bass to check...no signal coming from the tweeter, the noise which was present without a signal was still there and remained unchanged, the woofer worked fine.

I took out the crossover circuit to have a look at the components, nothing looks charred, nothing smells, fuses look fine...

I guess does anyone have any ideas about checking the crossover for issues? I've looked through all the posts on the forum related to the amp to get this far but i seem to be stuck. The crossover daughterboard doesn't seem to be on the schematic which ive been using

http://music-electronics-forum.com/a...457sch_0-1.pdf

[gbono]

see schematic - check connections and light bulbs...

[Jazz P Bass]

The bias adjust should have nothing to do with 'hum'.

I would think main filter capacitors first.

Can you post a pic of the crossover as there is very little info available about it?

[exspes]

There we go. The PCB seems to exactly as the BA115HA that you posted gbono, minus some of the parts. Going through the components the bulbs had low resistance of 2ish ohms so they're working, the capacitors showed resistance of 0 initially and rising to infinite resistance over time so they're working too, all the jumper wires checked out however the inductor L1 seems to be showing infinite resistance...which i think means it's broken? is it even possible to break an inductor :\

[gbono]

Check the solder joints on the other side of the PCB.................

[exspes]

Check the solder joints on the other side of the PCB.................

Solder joints are fine, shiny, non-oxidized. I clipped the multimeter onto the initial windings of the inductor and not the solder joints just to make sure it wasn't a connectivity issue and the resistance was still infinite.

Edit: Attached image of underside of the the board

[gbono]

You could try shorting out the inductor and playing a high frequency signal (>3KHz) to see if the piezo tweeter now works. If that is successful then the inductor is open circuit and would need to be repaired or replaced.

[exspes]

I did just that and it turns out you were right gbono i jumped the inductor and it came out just fine. i replaced the inductor with something i had laying about from an old TV and it worked perfectly Thanks so much for your help both of you, now my amp has the ping it's been sorely missing.