Power Supply problem with TR-707

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Maschinengeist
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Re: Power Supply problem with TR-707

Post by Maschinengeist » Wed Feb 24, 2010 4:34 am

After D1 you should get about 11.3 VDC and 5 VDC at the regulator (your black probe on the common and the red one on the out pin). Let's see if the +5 VDC circuit is fine.

About the external power supply, it's normal that it reads 14 V without a load. It works ok.
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Re: Power Supply problem with TR-707

Post by JRock » Sat Feb 27, 2010 12:29 am

Alright. finally got my 2.2 and 4.7 ohm fusing resistors. Just installed them. Same thing that happened before. Lights dance and it won't reset or go into test mode. This adapter is 700mA so it's a little closer. After D1 I get 13V(but this power supply read a little more than 16V) The +5 transistor reads 5v on one side and 13v on the other so everything is in working order with that.

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Re: Power Supply problem with TR-707

Post by JRock » Sat Feb 27, 2010 12:46 am

From D2 it reads -10v. Q2 reads -6v and Q1 reads - 12.5v. I guess that means the power is ok? It lights up again and the led's do a dance but it still won't reset or go into test mode. The LCD doesn't come on either... What's my next step?

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Re: Power Supply problem with TR-707

Post by Maschinengeist » Sat Feb 27, 2010 3:55 am

If you get -10V and +5V and you get a light show it means that the problem is elsewhere outside the power supply. We'll have to move toward the CPU just to see if there's not a defective component overpowering the 707.

Wish I had a 707 to test on as we speak. It would be faster. But hey, it's an educational journey, isn't it? I'll upload more schematics to help us out.

A bad Xtal (always near the CPU) can make the machine dance. The 707 has a 4MHz one. Need to test at least a frequency counter or an oscilloscope. Or a little building with a breadboard. Or if you have a part supplier near you, you can grab a new one (common part), change it and see.
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Re: Power Supply problem with TR-707

Post by JRock » Sat Feb 27, 2010 7:01 am

I have an oscilloscope. First thing 2mw I'll see if I can't find how to test the xtal on google. I'll check radioshack for it too. If they don't have one then I'll order one. I need to get some pots anyway. We're getting close. I can feel it!
You Rock!! Thanks a lot.

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Re: Power Supply problem with TR-707

Post by JRock » Fri Mar 05, 2010 1:39 am

Howdy. I tried an Xtal from my glitchy R8 but it still did the same thing. So I put the original back and now my R8 won't load up. Should I try a different one? I'm not positive that was 4MHz, but I think it was. Should I still go ahead an order another one?
I spent the last 4 days searching for a local component or surplus store and they don't seem to have 'em around here anymore. Maybe Philly or Trenton...
Just giving an update. Thanks

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Re: Power Supply problem with TR-707

Post by Maschinengeist » Fri Mar 05, 2010 3:30 pm

The R-8 uses a 12 MHz one. It's important to use a crystal of the same rating. If it behaves after putting in back the R-8 (assuming it has not been damaged), then recheck your solder joints. It's not normal.

To test it with an oscilloscope: http://www.electronicrepairguide.com/ho ... ystal.html. Use the formula f=1/T. In other words, frequency in Hertz = 1/time in regards to your time/div setting on your oscilloscope.

Using the keywords "how to test a crystal with an oscilloscope" on Google, it should pop some hits. If not, please let me know and I'll prepare something for you.
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Re: Power Supply problem with TR-707

Post by JRock » Fri Mar 05, 2010 11:54 pm

HA HA...
12MHz... Of course!!!
I'll get on that. Thank you.

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Re: Power Supply problem with TR-707

Post by JRock » Sun Mar 07, 2010 6:32 pm

I hooked the scope up to the pins on the x but I'm not getting anything. I'm not positive that is the way to test it though. I had trouble finding where to attach the probes. I tried it with a probe on ground too and still the same. It's powered up but I can't get a reading on the xtal.
I got a 4MHz and a 12 MHz coming from digikey so...
The Led's stopped dancing. Just the Cartridge light comes on now. I'm gonna check all the connections with my meter.
I fixed a DR-110 yesterday! Most of the buttons didn't work and the traces around the buttons were badly corroded. Works like new now!!!

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Re: Power Supply problem with TR-707

Post by JRock » Fri Mar 12, 2010 1:07 am

The 4MHz xtal arrived and still only the cartridge light comes on and no sound...
Are they polarized? It doesn't look like it.
I have and adjustable power source kit on the way from Adafruit.
They say they're reliable and maybe I'll learn something too... But that won't ship for 10-14 days.
What's next?
This is frustrating...
A lesson in patience and perseverance
Thank You

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Re: Power Supply problem with TR-707

Post by Maschinengeist » Fri Mar 12, 2010 8:22 pm

Ok so the 707 stopped to dance a little. That's good news.

I'll prepare something for you. Oh and no, a xtal is non-polarized.

[EDIT] I forgot to mention that the crystal cannot be tested if not hooked to a power source.
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