Amp

[Deigh]

I have gained an amp made by HBA Electronics of Napier New Zealand and they seem to have gone out of business. The make of the amp is STINGA and it is a 50 watt guitar amp.It should (and did) work on 240v AC and 12v DC when I got it a month ago. There were several places where some terrible bodging had been done but because the amp is of a size and weight suitable for my use I decided to tidy it all up and add a 12v battery.

All this I did, but to my disgust and surprise the amp will not work at all now! I removed some loose wires and obviously they were more important than I expected. The speaker seems to be completely out of the circuit and despite poking around I cant find out why.

Has anyone got a circuit diagram for this device?

I am fairly capable as a solderer and have a small knowledge of electronics. This has been enough in the past to get me out of trouble but now I'm floundering!

 

[GreenGiant]

I removed some loose wires and obviously they were more important than I expected. The speaker seems to be completely out of the circuit and despite poking around I cant find out why.

You removed some wires and now it doesn't work??
How strange...

First off we would need a model number, pictures of the internals, and the specs on the battery that you used

Guitar amps take a lot of current (50W @ 12V = 4.2A) so your battery may not be able to handle the current needs and therefor nothing will work, especially if the battery has overcurrent protection.

 

[Deigh]

amp 2

I can just imagine the disdain on your face when you read my query! I should have guessed that would happen and thought out my question a bit better! Here is a bit of background about me. I'm 83 years of age and have earned my keep as a fireman, wireless operater, musician, pilot, painter and fitter-turner. My wife and I live in a bus I converted to a motorhome twelve years ago. We lost our house and savings a few years ago when the markets crashed. In my life I have repaired hydraulics, pneumatics, electronics, electrics and even computers Most things rely on logic to fix! At the moment am doing panel beating rust repairs on the roof of my 'bus.

As a jazz guitarist I needed a lightweight amp running 240v and 12v just for off the cuff sessions at campervan rallies and picked this one cheap off the internet. It worked well on mains (no battery supplied) and I decided to tidy it up for keeping. The jack plug sockets for headphones and line out were hanging loose and the nuts retaining them were missing. Couldn't replace them and I don't need what they do so I removed them. I said in my first mail that I'd cut them, This was not true, I actually unsoldered them. If I had cut them I would have been able to see where they came from and replaced them when I found the amp not working! Now I'm not sure and need a circuit diagram to guide me. The speakers seem to have got isolated and I need to know what part of the circuit is usually connected to them. I am mainly trying to get it back to working on 240v and will play around with battery when it works again.

Serial number S20-0076 is scratched by hand on the chassis but there is no model number except for the identification 220-249v ac 50watts STINGA. The speaker connections are numbered 7 and 8 The black wire is attached to 7 (unaltered) and I have re-soldered the white to 8, this I am not positive was the way it was before.

Where to now?
Deigh

 

[(*steve*)]

The headphone jacks may include a switch that turns off the speakers when the headphones are inserted.

If this is/was the case, then the signal flows through the wires connected to the headphone socket. Removing them will effectively break the signal path.

If those jacks are mono, and have three wires attached, then this is almost certainly the case.

One of the connections will be to ground, the other will be the output from the preamp stage and the input to the main amp for that channel. Connecting those together would be the right thing to do.

If you are not sure of which connection is which, DON'T connect anything straight away as you might cause damage.

 

[Deigh]

Thanks for that info, will start poking around shortly.

On of the back of the chassis is a socket labelled DC12v. (bottom right hand side of the picture) I presumed from the start that this was a means of running the amp off 12v. Now the penny has dropped that since there was no switch alongside it then it must be a source of 12v for running accessories!

What do you think?

 

[duke37]

I would not think that the 12V socket is a source.

There is an integrated circuit with about 5 legs shown in the photo. this is likely to be the audio amplifier. If you get the details of this, you can check whether there is the correct voltage on each pin (do not short pins together) and you can find the output. This will go through a large electrolytic capacitor to the speaker. Thus you can find the output connection.

 

[(*steve*)]

Pin 1 of that IC looks a little dodgy to me.

 

[Deigh]

There is an integrated circuit with about 5 legs shown in the photo. this is likely to be the audio amplifier. If you get the details of this, you can check whether there is the correct voltage on each pin (do not short pins together) and you can find the output. This will go through a large electrolytic capacitor to the speaker. Thus you can find the output connection.[/QUOTE]

Yes, it looks rather dodgy as though someone has done some awful soldering on it. Tried to purchase a new one yesterday but my local supplier has nothing with 5 legs on it. The whole kit looks as though it is about 10 to 15 years old so that unit is probably no longer on the market. Will do a re-solder job on it and hope for the best.

 

[CocaCola]

Tried to purchase a new one yesterday but my local supplier has nothing with 5 legs on it.

You don't chose parts by leg count alone, that only identifies the package not what is inside the chip What are the numbers on the the chip, that will identify the chip...

 

[Deigh]

[QUOTE=CocaCola;1516064]You don't chose parts by leg count alone, that only identifies the package not what is inside the chip What are the numbers on the the chip, that will identify the chip...[/QUOTE]

Yeah, I know that but the identification letters of TDA 2030A and SCS 88640 meant nothing to the supplier and she added "We aint got anything with five legs anyhow"

Truth is that I have no idea on how to replace the unit with a four legged piece, so I just gotta have a leg for every hole in the board.

 

[CocaCola]

Yeah, I know that but the identification letters of TDA 2030A and SCS 88640 meant nothing to the supplier and she added "We aint got anything with five legs anyhow"

Wow, you need a new supplier... TDA 2030A is a dead giveaway, that is a common chip and just about any well stocked supplier should have it on hand or be able to get it and should have immediately recognized what it was...

http://www.mouser.com/Search/Refine.aspx?Keyword=TDA+2030A

http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=tda2030a

 

[duke37]

Lokking up the data from ST gives the following information.

Counting from the RIGHT.
1. Audio input at half of supply voltage.
2. Feedback, same as output voltage.
3 and TAB. Ground
4. Output, should be half supply voltage.
5. Supply

Measure the voltages with a sensitive meter.
Trace through from pin 4, through a big capacitor to output connection.
Touching pin 1 should give a hum.

 

[quantumtangles]

Do capacitors self harm?

Two very suspicious looking holes in the circuit board can be seen beside the marking "13", ...one of which is accompanied by a "+" sign.

Has an electrolytic capacitor committed suicide by falling off the circuit board?

In fact it is unlikely to have been an electrolytic (cylindrical) capacitor as there is no white circle around the component as with the other caps (if there ever was a component there). My guess, assuming there really are two ominous holes in the printed circuit board, is that a carbon film resistor has fallen off and the "+" sign relates to another component.

 

[Deigh]

Two very suspicious looking holes in the circuit board can be seen beside the marking "13", ...one of which is accompanied by a "+" sign.

Has an electrolytic capacitor committed suicide by falling off the circuit board?

Behind the hole is a blob of solder the residue of whatever had been there. Cant find any other unused hole so it is difficult to explain away. It is connected to the 13 lug.
mystery!

 

[Deigh]

Wow, you need a new supplier... TDA 2030A is a dead giveaway, that is a common chip and just about any well stocked supplier should have it on hand or be able to get it and should have immediately recognized what it was...

http://www.mouser.com/Search/Refine.aspx?Keyword=TDA+2030A

http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=tda2030a

Now, be realistic. New Zealand has only four million inhabitants so there aint a lot of electronic suppliers. My local one is 15 miles away, the next one is 40 miles away. If the local one hasn't got it then I'm plumb out of luck!

 

[Deigh]

Lokking up the data from ST gives the following information.

Counting from the RIGHT.
1. Audio input at half of supply voltage.
2. Feedback, same as output voltage.
3 and TAB. Ground
4. Output, should be half supply voltage.
5. Supply

Measure the voltages with a sensitive meter.
Trace through from pin 4, through a big capacitor to output connection.
Touching pin 1 should give a hum.

Thanks, will do some testing shortly.

 

[Jeffpepin]

You removed some wires and now it doesn't work??
How strange...

 

[Jeffpepin]

TDA2030A are know to Blow ! . same problem on a rebel K20G guitar amp . get it blow . tried to get a replacement ic . ebay look around 25bucks

 

[Jeffpepin]

wow now 1.27$ just here on ebay

 

[Deigh]

test shows that 2030A is not working properly, will look for a replacement, if I can only get a four pin equivalent would I presume that the earth pin would be missing?