eqt with low output voltage

marko · 31st December 2006, 03:33 PM

i have 3 eqt's but one struggles to make 5v output whilst the other 2 are well over the rates 9v. any idea why this might be? i did notice the transformer gets a little hot too...

1moreamp · 1st January 2007, 06:46 AM

Check you B+ voltages and your + - rail voltages feeding the chips in the EQT.
I have seen power transformer failure, and or OP-amp chip failure cause voltage drops like you have.

Happy New Year ! Good Luck

marko · 1st January 2007, 01:32 PM

think this may be above me! only reason i wanted to fix it is because it's from a matching pair, the 3rd one has a green board in it and most likely made in the far east....as you can tell that tranny has been replaced at some time!

marko · 1st January 2007, 01:36 PM

and the good one with the green board...

1moreamp · 1st January 2007, 07:09 PM

Nice Pics, Thx.
The LTC power device does fail from time to time, But be forewarned that this is typically a sign that the transformer is shorted on itself. The LTC is fairly cheap to come by here locally, but you will have to contact Audio Control for the transformer.

If your out to just save that board, then you could just swap parts to do the rescue/repair, or just order the LTC1070 I think it is from just about any source and try and replace it first, in hopes that will solve the issues.

try this to find your parts: http://www.findchips.com/avail

The transformers should just exchange across. It would be nice to read the rail voltages at the chips, referenced to ground of the RCA shield.
The voltage test points for those 14 pin op-amps are numbers 4 & 11.

These two pins have the rails on them. You might have a bad op-amp chip in one of the filter bands causing the excessive load on the power supply. A single blown eq band will cause this sometimes. The power supply in these EQT's were not intended for a very large load, so any chip failure would result is voltage drop.

The fact its trying to work tends to indicate that it might just be a power supply issue, possible the transformer, or the LTC1070 device, But it could be a op-amp or two that went south on you.

On another note, Audio Control might have flat rate repairs at their facility listed below:
http://www.mobileaudiocontrol.com/contact.asp

Good Luck, and Happy New Year

marko · 1st January 2007, 09:10 PM

thanks for the detailed responce as usual!! you helped me resurect my 0.5 on sb not so long ago..

as for the cost of fixing, will have to look into it but for what they go for these days on ebay it might be just as cheap to buy a single unit off ebay!

1moreamp · 2nd January 2007, 12:19 AM

Yeah I remember Marko. Hows that doing so far? Well I hope. Have you tried Phoenixphorum yet ? if not here ya go

http://phoenixphorum.com

I hang around there alot nowadays. Anyway, always glad to help

Cheers !

31st December 2006, 03:33 PM	#1
marko diyAudio Member Join Date: May 2004 Location: donnyuk	eqt with low output voltage i have 3 eqt's but one struggles to make 5v output whilst the other 2 are well over the rates 9v. any idea why this might be? i did notice the transformer gets a little hot too...

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1st January 2007, 06:46 AM	#2
1moreamp diyAudio Member Join Date: Dec 2005 Location: Northern California	Check you B+ voltages and your + - rail voltages feeding the chips in the EQT. I have seen power transformer failure, and or OP-amp chip failure cause voltage drops like you have. Happy New Year ! Good Luck

1st January 2007, 07:09 PM	#5
1moreamp diyAudio Member Join Date: Dec 2005 Location: Northern California	Nice Pics, Thx. The LTC power device does fail from time to time, But be forewarned that this is typically a sign that the transformer is shorted on itself. The LTC is fairly cheap to come by here locally, but you will have to contact Audio Control for the transformer. If your out to just save that board, then you could just swap parts to do the rescue/repair, or just order the LTC1070 I think it is from just about any source and try and replace it first, in hopes that will solve the issues. try this to find your parts: http://www.findchips.com/avail The transformers should just exchange across. It would be nice to read the rail voltages at the chips, referenced to ground of the RCA shield. The voltage test points for those 14 pin op-amps are numbers 4 & 11. These two pins have the rails on them. You might have a bad op-amp chip in one of the filter bands causing the excessive load on the power supply. A single blown eq band will cause this sometimes. The power supply in these EQT's were not intended for a very large load, so any chip failure would result is voltage drop. The fact its trying to work tends to indicate that it might just be a power supply issue, possible the transformer, or the LTC1070 device, But it could be a op-amp or two that went south on you. On another note, Audio Control might have flat rate repairs at their facility listed below: http://www.mobileaudiocontrol.com/contact.asp Good Luck, and Happy New Year

1st January 2007, 09:10 PM	#6
marko diyAudio Member Join Date: May 2004 Location: donnyuk	thanks for the detailed responce as usual!! you helped me resurect my 0.5 on sb not so long ago.. as for the cost of fixing, will have to look into it but for what they go for these days on ebay it might be just as cheap to buy a single unit off ebay!

2nd January 2007, 12:19 AM	#7
1moreamp diyAudio Member Join Date: Dec 2005 Location: Northern California	Yeah I remember Marko. Hows that doing so far? Well I hope. Have you tried Phoenixphorum yet ? if not here ya go http://phoenixphorum.com I hang around there alot nowadays. Anyway, always glad to help Cheers !