Power Supply problem with TR-707

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JRock
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Power Supply problem with TR-707

Post by JRock » Sat Feb 06, 2010 6:28 am

Anybody opened up a TR-707? Mine won't power up at all. I replaced the jack and the +5v regulator (attached to the heatsink behind the switch) and that didn't do anything. I can't figure out which component controls the -10v. When I flip the switch the voltage drops to 2.15v so I guess that's my next move. I don't know much about electronics so I really need help with this. If any of this sounds familiar to someone who knows what they're doing I would really appreciate some input. The PSU I'm using is DC12v tip negative(not the original.) when I hit the switch nothing at all visible happens (but like I said, I can see on the multi meter that the voltage on the jack pins drops to 2.15v where without hitting the switch it reads 12v.)

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Re: Power Supply problem with TR-707

Post by Maschinengeist » Sat Feb 06, 2010 4:37 pm

I'll try to find time to look at my service documents
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Re: Power Supply problem with TR-707

Post by JRock » Sat Feb 06, 2010 5:50 pm

I really appreciate it man. Thanks

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Re: Power Supply problem with TR-707

Post by Maschinengeist » Sun Feb 07, 2010 4:27 am

In one technical newsletter I've got about the tr-707 there is a mention about a problem with the fusible resistor R49 on the voicing board. Change the 2.7 Ohm 1/4W to 1/2W.

TEST IT FIRST BEFORE CHANGING IT

Generally, the culpit in a power supply are the diodes. Have a look at them. After comes the transistors (Q1, Q2)
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Re: Power Supply problem with TR-707

Post by JRock » Mon Feb 08, 2010 4:50 pm

Thanks. I'll check that out today.

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Re: Power Supply problem with TR-707

Post by JRock » Tue Feb 16, 2010 3:23 am

I can't find the values for the diodes in the power supply. I checked the service manual but they're not givin up the goods. Still have to find R47 and give that a try...

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Re: Power Supply problem with TR-707

Post by Maschinengeist » Tue Feb 16, 2010 4:57 am

You don't need the values to test them. Here how to test them (minus the Zener & Schottky ones, which are tested differently): http://www.kilowattclassroom.com/Archive/AN0001.pdf
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Re: Power Supply problem with TR-707

Post by JRock » Tue Feb 16, 2010 6:43 pm

Thanks! unfortunately my multimeter took a c**p on me. I changed the batteries and still no good readings. That's what I get foir buying a $30 jobby at Radio Shack. I'm dead in the water till I get another one. If I remember correctly I wasn't getting any reading from the 2.7 in R49. I honestly had no idea what it was. I don't think I'll be able to find that at the shack so I'll check digikey and mouser. Thanks a lot...

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Re: Power Supply problem with TR-707

Post by JRock » Sun Feb 21, 2010 6:16 am

Got my multimeter back up and running. Turns out it was the fuse, Funny cause it still powered up, just gave funky readings. I'm guessing it is T1, the DC/DC transformer. I don't know too much about them but the diodes and the transistors all seem to check out. I'm not real clear how to check a transistor but I looked it up and both q1 and q2 read open from the base (?) out and closed from the collector/emitter(?) in. I couldn't even find anything on how to test a dc/dc converter with a multimeter but it makes sense that it would be something like that since the power drops to 2.15 and that's right in the -10v section... R49 is reading 2.7xx ohm so I think that's ok. If my logic seems faulty then please let me know. I'm going to order the same part from vintage planet and see if it doesn't do the trick.
Thanks

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Re: Power Supply problem with TR-707

Post by Maschinengeist » Sun Feb 21, 2010 7:54 am

I always forget to ask about the fuse. I guess I presume everyone check that first.

If you don't know too much about testing with a multimeter, please stop venturing in there. You might do more damages than good.

If your 707 works now, please leave it as it is. If it still act funky, post in here and we'll try to help you out.
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Re: Power Supply problem with TR-707

Post by JRock » Sun Feb 21, 2010 7:01 pm

I am truly grateful for your wisdom. I couldn't have gotten this far without your expert knowledge and advice. I don't know anything about you in the real world but I see your help and advice on lots of other threads too. I have gleaned that you know what you are doing very well.
Rest assured that I'm being very ginger. I figure it doesn't work anyway so I've got nothing to lose and everything to gain. Probably happened to a lot of people and they just threw it out, but I know this is a beautiful piece of Vintage equipment that will not be remade. I treat it with the proper delicacy when I am inside it. I'm a stone mason by trade and I'm laid off right now so I have lots of time and little to no money. I can't afford to take it to a service center. I am pretty new to the world of electronics and synthesizers but I love it!! This is how I learn. You have to start somewhere. I put together a tube preamp kit from Paia and I've been able to fix my stomp boxes. I got a Juno with 4 dead voice chips and I was able to revitalize them and recalibrate it. I figured out how to fix a dead key on my Jx-3p and crank up the resonance. I got a x0xb0x pre-assembled but I've been able to add lots of modifications to it. Lots of things end up working out of guesses or luck and sheer determination but I learn every time I do something new. I went from not having any idea how to use a multimeter to knowing pretty well how to use it (thanks to some help and tutorials) in maybe 2 months... I plan on building my collection of Vintage synthesizers as well as maybe getting some new ones but right now I can't afford to take them to a tech every time have an issue. There are other people out there that have the same problems and maybe next time I can be the guy with the solution and the knowledge. Again Thank You so much for your time, your knowledge and your patience!!! I'll keep you posted if the DC/DC converter works.

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Re: Power Supply problem with TR-707

Post by Maschinengeist » Mon Feb 22, 2010 3:10 am

Thank you for the compliments. I am not used to that.

Don't despare, we'll have your 707 up and running. I'm quite busy these days and can only afford to write 1 or 2 liners, as you might have noticed.

Lemme check my service manual, which I didn't have time to do so far. Nor get near my simulation program.
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Re: Power Supply problem with TR-707

Post by Maschinengeist » Mon Feb 22, 2010 3:47 am

The power supply schematic:

Image

We'll work from there
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Re: Power Supply problem with TR-707

Post by JRock » Tue Feb 23, 2010 1:49 am

Ok, I got a new power supply, 12vDC. It was 1.5A and the 707 only needs 250mA so that should have been alright. I plugged it in and the leds started doing a little dance! I tried to reset it and I tried to put it in test mode but it was nothin' doin'. Checked for tip negative. I turned it off and on and still the same charade. I plugged the audio in and the drums were playing randomly. Tried stop and all the other options but to no avail. Turned it off and when I tried to turn it on nothing happened. Frustrating. I checked the voltage on the PSU and it was 16V!!! So now R49 is burnt out. But all the diodes still seem to check out ok. I can't find it in digikey or mouser so I ordered a 2.2ohm and a .47ohm 1/2w 250V fusible resistor. I'm hoping this is close enough if I run them in serial. They shipped it today so I'll put them in, find another PROPER PSU (test the voltage first) and maybe I'll be good to go. My other PSU reads 12V and 300mA but this machine isn't havin that one. I read that they can be particular about their power. Senso from Vintage Planet told me T1 the DC/DC converter was only to control the LCD, so he won't send it to me yet. We can cross that bridge when we come to it.
Again Thank You for all your help. I wouldn't be this far without your Counsel. I'll update you as soon as I put the fuses in. If you think that I need the exact value then let me know.

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Re: Power Supply problem with TR-707

Post by JRock » Tue Feb 23, 2010 6:30 pm

Ok, I got another 12V DC PSU and this one is reading 16V too!!! I don't think it's my multimeter cuz my battery reads 1.5 and my old PSU still reads 12V. I made a 9VAC PSU out of an old 12VDC adapter and that is reading 14.5V, but it works fine. Maybe PSU's don't have to be as precise as I thought. My old PSU I tried to use on the 707 was selectable but it reads what it's supposed to. Right now I have it set on 9V and that's what it reads. When I had it set on 12V it read 12V, but it wouldn't work to power my 707. What's going on???

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