Hey all,
I'm trying to restore a technics su-v7 amp that is showing its age. It has speaker hum, a couple dodgy potentiometers and is generally not performing at its best. However, I'm really stuck.
I know basically what I want to do - give the amp a complete recap and replace the volume/balance pots. However, I'm struggling to find the correct components, there's so many numbers!
I was wondering:
does anyone know of a complete parts list for this amp?
where can I obtain these parts? (maplin don't seem to stock all of them)
has anyone successfully restored one of these and knows which exact parts I can use?
I have a schematic for the amp if it's helpful...
very confused, don't want to mess this up as it's my second best amp... but there's nobody around here who restores them!
thanks in advance for any help - sorry for so many questions!
I'm trying to restore a technics su-v7 amp that is showing its age. It has speaker hum, a couple dodgy potentiometers and is generally not performing at its best. However, I'm really stuck.
I know basically what I want to do - give the amp a complete recap and replace the volume/balance pots. However, I'm struggling to find the correct components, there's so many numbers!
I was wondering:
does anyone know of a complete parts list for this amp?
where can I obtain these parts? (maplin don't seem to stock all of them)
has anyone successfully restored one of these and knows which exact parts I can use?
I have a schematic for the amp if it's helpful...
very confused, don't want to mess this up as it's my second best amp... but there's nobody around here who restores them!
thanks in advance for any help - sorry for so many questions!
An old fashioned TV repair technician with a service manual could trouble shoot your amp. These guys really know their trade.
Hi Andrew T, sure they are...
But maybe he want to repair it your shelf 🙂
Hi ashleycox, do you measure the rail voltage & offset?
Then you can find which parts should be changed & don't change it to much 😀
Regards
But maybe he want to repair it your shelf 🙂
Hi ashleycox, do you measure the rail voltage & offset?
Then you can find which parts should be changed & don't change it to much 😀
Regards
Hi John,
this is the thing... I'm a 'noob'. How on earth do I do that? 🙂
this is my first real restoration project - truthfully I just want to get it restored. Don't have to do it myself, but I can't find anybody in my area who offers a repair service - just the typical 'just replace it' sales people.
I don't have any decent measuring tools, only a general purpose multimeter.
You might not need to replace the potentiometers. A good cleaning with contact cleaner and lube might solve some of your problems and leave you more money for your caps.
I rebuilt a PS section of a Marantz 2235 receiver. I did a visual on the board involved and ordered and replaced all the caps and semiconductors. It worked great. I got some of the caps in higher voltages than what were on the board, but going higher is fine. I went through Digi-key DigiKey Corporation - Electronic Components Distributor for my parts.
Mike
I rebuilt a PS section of a Marantz 2235 receiver. I did a visual on the board involved and ordered and replaced all the caps and semiconductors. It worked great. I got some of the caps in higher voltages than what were on the board, but going higher is fine. I went through Digi-key DigiKey Corporation - Electronic Components Distributor for my parts.
Mike
This is diyaudio.com, oddly enough. There are websites where the answer to every question is "hire a qualified technician". I don't spend much time on those.
A simple google search of your make and model got this and a couple of others if this is not free enough http://www.google.com/url?sa=t&rct=j&q=technics%20su-v7%20schematic&source=web&cd=12&cad=rja&ved=0CGsQFjAL&url=http%3A%2F%2Fwww.manualslib.com%2Fmanual%2F387810%2FTechnics-Su-V7-Service-Manual.html&ei=04SeUMqwOoaBywGO7YCQDw&usg=AFQjCNEglvi-8yeZmCmdTdMjdX6-vxo-dw
I wrote a tutorial on recapping transistor organs for this guy Could anyone please help me out with a Thomas Trianon? Same process for a transistor amp, but fewer connectors. I've got a different tutorial for tube (valve) projects, the cap installation is a bit different as are the vendors.
He never followed through, but this is a hobby, not a profession, they don't fire you for not finishing. Just your project has to go in the dumpster at some point if you don't finish. The devices in my tag line are projects that I've finished, more or less. The Wurlitzers and two Hammond organs excepted. I love not working, puzzles to solve every day, and the parts are usually under $100.
Personally I don't measure much of anything on audio devices over twenty years old that sound funny- the calender gives me measurement enough. If they sort of work, then new electrolytic caps might help- and usually do. I do a couple at a time to focus my eyes on my mistakes. Don't touch 2 things at a time with the power on, voltage over 25 crossing your heart can kill you. Don't wear jewelry at any voltage. Get a clip lead for the negative probe of your DVM, so you only have to use one hand measuring. In the UK, farnell.com operates, and mouser.com has a warehouse on the continent somewhere. I've used the US branches of both with good satisfaction. Farnell has the hours life of caps in the selector table, I don't like to install those with life <3000 hours since I've had to re-e-cap the dynakit stuff 3 times in 40 years.
Pots, you measure the shaft size, you measure or read the maximum resistance, you pull up the matching pots from the selector table and try to find something that you can make work. Jumper wires, separate mount boards, etc are tricks you can use to adapt something to the position you've got that you can't buy the exact match in quantities less than 10000 each. Usually you want audio/log taper except maybe on tone controls.
A simple google search of your make and model got this and a couple of others if this is not free enough http://www.google.com/url?sa=t&rct=j&q=technics%20su-v7%20schematic&source=web&cd=12&cad=rja&ved=0CGsQFjAL&url=http%3A%2F%2Fwww.manualslib.com%2Fmanual%2F387810%2FTechnics-Su-V7-Service-Manual.html&ei=04SeUMqwOoaBywGO7YCQDw&usg=AFQjCNEglvi-8yeZmCmdTdMjdX6-vxo-dw
I wrote a tutorial on recapping transistor organs for this guy Could anyone please help me out with a Thomas Trianon? Same process for a transistor amp, but fewer connectors. I've got a different tutorial for tube (valve) projects, the cap installation is a bit different as are the vendors.
He never followed through, but this is a hobby, not a profession, they don't fire you for not finishing. Just your project has to go in the dumpster at some point if you don't finish. The devices in my tag line are projects that I've finished, more or less. The Wurlitzers and two Hammond organs excepted. I love not working, puzzles to solve every day, and the parts are usually under $100.
Personally I don't measure much of anything on audio devices over twenty years old that sound funny- the calender gives me measurement enough. If they sort of work, then new electrolytic caps might help- and usually do. I do a couple at a time to focus my eyes on my mistakes. Don't touch 2 things at a time with the power on, voltage over 25 crossing your heart can kill you. Don't wear jewelry at any voltage. Get a clip lead for the negative probe of your DVM, so you only have to use one hand measuring. In the UK, farnell.com operates, and mouser.com has a warehouse on the continent somewhere. I've used the US branches of both with good satisfaction. Farnell has the hours life of caps in the selector table, I don't like to install those with life <3000 hours since I've had to re-e-cap the dynakit stuff 3 times in 40 years.
Pots, you measure the shaft size, you measure or read the maximum resistance, you pull up the matching pots from the selector table and try to find something that you can make work. Jumper wires, separate mount boards, etc are tricks you can use to adapt something to the position you've got that you can't buy the exact match in quantities less than 10000 each. Usually you want audio/log taper except maybe on tone controls.
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As a first project this is probably out of your depth, there are no end of places where that hum could be coming from so you could spend a lot of money and effort and just end up with a costly learning experience. Simply taking the thing to bits and cleaning the contacts, reassembling and testing is worthwhile, at least you'll find out how the bits fit together.
There is a service manual out there, just google for it and you'll find one on madambutterface site. The admins here don't like copyright protected material being posted.
There is a service manual out there, just google for it and you'll find one on madambutterface site. The admins here don't like copyright protected material being posted.
DIY?
Someone who wants to repair something themselves, needs to feel confident to proceed. This is not a simple amplifier. It uses servos and the protection, servo and current control circuitry is extensive. It's discrete plus IC and if simply doing a shotgun capacitor swap, there is going to be trouble with voltage thresholds that will be impossible to sort without good knowledge of the design and practice of sorting it. It's not a big Hybrid chip or a basic DIY circuit, this is complex.
Sure, replace the 2 big electrolytics with similar or up to 100% higher value capacitance (read it as microfarads) but never use any voltage rating less than that marked on the capacitor. You can't miss them. If all that you otherwise really need to do is wash out the pots while rotating the control to clear up the scratchiness, do so with an electrical contact cleaner but don't flood the amplifier. You wont need more than those 2 quantities to specify the caps and the pin spacing + overall dimensions so they fit on and in the board etc.
Beyond those steps, I strongly agree with AndrewT's advice to take it to a tech who will be able to avoid issues with the safety circuits. Recapping is easy to say and understand but the amplifiers are not all a piece of cake to troubleshoot, should your best laid plans come up ugly. Meantime, read the many, many recap threads that noobs start here and find out their problems before you run into them too. 🙂
Someone who wants to repair something themselves, needs to feel confident to proceed. This is not a simple amplifier. It uses servos and the protection, servo and current control circuitry is extensive. It's discrete plus IC and if simply doing a shotgun capacitor swap, there is going to be trouble with voltage thresholds that will be impossible to sort without good knowledge of the design and practice of sorting it. It's not a big Hybrid chip or a basic DIY circuit, this is complex.
Sure, replace the 2 big electrolytics with similar or up to 100% higher value capacitance (read it as microfarads) but never use any voltage rating less than that marked on the capacitor. You can't miss them. If all that you otherwise really need to do is wash out the pots while rotating the control to clear up the scratchiness, do so with an electrical contact cleaner but don't flood the amplifier. You wont need more than those 2 quantities to specify the caps and the pin spacing + overall dimensions so they fit on and in the board etc.
Beyond those steps, I strongly agree with AndrewT's advice to take it to a tech who will be able to avoid issues with the safety circuits. Recapping is easy to say and understand but the amplifiers are not all a piece of cake to troubleshoot, should your best laid plans come up ugly. Meantime, read the many, many recap threads that noobs start here and find out their problems before you run into them too. 🙂
If the OP is willing to work on this as he can afford, I say go for it. A couple of years ago I posted about an HK 330A on a different forum. It was having some issues and I was trying to trace what they might be via a schematic that was supposed to be for a 330A; however, the schematic and the receiver didn't quite agree. I posted asking for help and received advice along the lines of "if you can't read a schematic, you have no business working on this receiver!" A far cry from the DIY spirit. I can read a schematic and I still poke around with the 330A once in a while. It might be too much for me to fix, but I can still learn from it. I didn't order more than I could afford, and when I do get it working, I will be quite satisfied with my efforts.
With all that said, my advice to the OP is to start with the simple things and be patient. What looks like it might be a problem quite possible may not be. Recap the power supply and then isolate sections systematically (once you get the schematic) and see if the problem goes away. Search for and build a "dim bulb tester" and use it. Ask questions, post pictures, and share your results. Maybe another forum member has been thorugh the same issue or maybe someone has the parts you need cheaper than a vendor. Part of DIY is learning. Part of DIY is also failure. No big deal.
Be careful and take indianajo's advice about safety. When you're working with electricity, serious injury or worse is only a milliamp away.
Keep on asking for help and share your adventure! 😀
Mike
With all that said, my advice to the OP is to start with the simple things and be patient. What looks like it might be a problem quite possible may not be. Recap the power supply and then isolate sections systematically (once you get the schematic) and see if the problem goes away. Search for and build a "dim bulb tester" and use it. Ask questions, post pictures, and share your results. Maybe another forum member has been thorugh the same issue or maybe someone has the parts you need cheaper than a vendor. Part of DIY is learning. Part of DIY is also failure. No big deal.
Be careful and take indianajo's advice about safety. When you're working with electricity, serious injury or worse is only a milliamp away.
Keep on asking for help and share your adventure! 😀
Mike
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If you want to save your precious bit of trash, your complicated techniques reciever, for later when you are "qualified", you might look around for a sixties leak amp with issues. Things were simpler in 1966, a good place to start. Say a leak delta 70 or a leak 30. Broken. I lucked out my sT70 and PAS2 were pretty simple. The St120 transistor amp wasn't too bad, but took me 3 tries to get past the design issues. If I had started on this PV-1.3k amp I just spent the last 15 months repairing, I would have been very frustrated. The more complicated, the more you learn. But simple is where to start. But don't be too reverential of your Techniques, it is trash after all until after the repair is complete.
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With all due respect to the other posters, hear all the advice given and decide for yourself how far you're willing to go with this repair. If you're willing to be patient and don't mind some frustrations or failure, go for it. If you'd rather find something simpler, look for a vintage (70's) Pioneer, Sansui, or Marantz that needs work and put the Technics aside and play with it a little at a time.
Mike
Mike
Thanks for all your help. Took the lid off the amp earlier, incredibly complicated. Think I'll find something simpler to practice on, and get this one done by a professional - it's in use in a system, so it's not one i've just got lying around. It was worth a try, and will be useful for learning when I can get hold of something to practice on! 🙂
The hum you mention in post #1
Does it hum on all inputs ?
Does it hum with no inputs connected. That is just the amp and speakers and nothing else ?
Don't assume the amp is faulty... the hum could be something else.
Does it hum on all inputs ?
Does it hum with no inputs connected. That is just the amp and speakers and nothing else ?
Don't assume the amp is faulty... the hum could be something else.
it hums on all inputs with no sources connected (or near it for that matter), at low volume, even through headphones.
I would check for DC on the speaker output. Since it happens even with headphones, you might have DC getting onto the output signal before the output section to the speakers. If you have a lot of DC, that will cause a hum and it could trash your speakers. Does the amp have pre-in/out jacks? If so, disconnect them and see if it's still on your headphones. I'd be willing to bet it's in the preamp or before.
Mike
Mike
That sounds like a problem with the amp then. It may or may not be just some dried out caps but what the amp really needs is more detailed tests using a scope to see where the problem is. Without doing that its all guesswork and hoping a cap change will fix the problem.
The DC offset tests that others mention is worth doing too. There should be essentially zero volts DC across the speaker terminals. Anything over a few 10's of millivolts is a problem
The service manual specifies DC offset below 30mv when connected to an 8 ohm speaker. You need to get a service manual when dealing with anything complex.
A good way to learn is building some simple kits, get a thing working and see how chaning caps here and there effects the sound. There will be lots of help available on this board for people doing that sort of thing.
Old amps can be a good source for scrap parts: case, knobs and connectors; heatsinks for output transistor/chip, these are horribly over-priced when new; if working, the power transformer. A £20 scrap amp can have bits that from DIY specialists would cost you $200.
A good way to learn is building some simple kits, get a thing working and see how chaning caps here and there effects the sound. There will be lots of help available on this board for people doing that sort of thing.
Old amps can be a good source for scrap parts: case, knobs and connectors; heatsinks for output transistor/chip, these are horribly over-priced when new; if working, the power transformer. A £20 scrap amp can have bits that from DIY specialists would cost you $200.
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