Will do. I'm not for giving up. Thanks for getting back to me.

Replaced the chip - still the same. 

I have ordered two.  I'll let you know how I get on. Thanks for everyone's help. Could be a week or so before I know but I will be back.

Showing 18V at power supply.
1  17.8
4  17.8
8  0
12 0.22

collector - 9.9V I think this is correct very hard to see. The two other legs had about 0.2v. The transistor is a PN930.

Pins 1/4 showing 17.8V is a change though. Before I couldn't get anything I did have a look at the batt\mains switch as it was loose.

 Checks out as 100ohms between pin 1 and 4.  :dbtu:

I think I have manged to work out which pins are which. There is no voltage on pin 1 or 4. i.e.no supply voltage to the chip. From the bridge rectifier (18Vdc) it goes to a 1000uF 25v capacitor. I get 18v on one leg and 0V on the other leg.  That's how far I have got....                                                                                                                                                                                                                                 

No problem. Hopefully I can have a go at this come the weekend.

"If I am not mistaken, the heatspreader has tabs that solder to the ground tabs." - Correct. Hopefully I'll be able to have a good look soon as I'm a bit busy at the moment.
Thanks for all your input.
Steve

Yes, I know that.  I just can't see it because of the heat sink (?) or grounding arrangement on top of it. 

Hi Jazz, I understand all that so I will check it out in the next few days. I did have a quick look but it's hard to see the orientation of the op amp in relation to the pins. I might make a drawing to help with that and also rig up some sort of constant source input signal to aid troubleshooting.
Thanks again,
Steve

Hey Jazz, no problem at all. I should have posted the schematic on the opening post.
Steve.

Quote from: solderer25 on May 25, 2018, 03:04:30 PM
Hi. I am following this thread with interest as I too have a mains/battery Escort amp. I dont recognise the schematic posted previously though. The Vox Escort circuit I know uses a single transistor preamp and an old school TBA810 power amp chip. If the TBA810 is found to be duff it can be replaced (still available mail order I think) but is tricky to desolder/solder as the pins are staggered.

The chip is as cheap as chips on flea bay.

This is the schematic....

Thanks for getting back to me with you suggestion which I hadn't tried. I did what you said but still no sound. I also tested the continuity from the PCB to the speaker and that was good. For good measure I fed the external output into another amp and still nothing.

Hi Everyone,

New to the forum as I need some help..... 
Manufactured in the 1970's I have had this little Vox amp a long time. Saying that for a number of years it has sat in the corner in the room and the last time it was switched on it worked. Of course it doesn't now.  I can a hear very faint hum from it. And I mean really faint. I have to put my ear against the speaker cloth to hear it. Other than that there is no sound at all. I have done some basic troubleshooting using a DVM.

Checked input jacks - ok
Checked speaker - ok
Checked voltage output from transformer - ok
Checked PCB fuse ok.
Checked output from bridge rectifier - ok I think. Getting to the limit of my knowledge.

So, I think the problem is on the PCB. I have inspected it and I can't see anything obvious i.e. Component damage, dry joints etc.
I could take it to some repairer but I don't think it would be cost effective.

Anyway, here is the question -

For the components on the PCB which ones are the most liable to fail to end up with no output all?
I'm just thinking of replacing some of the components as they will be cheap and I'm not too bad with a soldering iron.
It's old school electronics so it shouldn't be too difficult to solder in new components.

I did manage to find a schematic of the PCB but I haven't done much troubleshooting of PCB's before.

Anyway, If anyone has any ideas how I can bring this little old amp back to life I would appreciate it.
Thanks,
Steve