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 Forum index » Instruments and Equipment » General Discussion
Yamaha DX7 Battery replacement issue
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Gothboy



Joined: Feb 21, 2006
Posts: 369
Location: Santa Monica, Ca.
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PostPosted: Fri Mar 01, 2013 7:15 am    Post subject: Reply with quote  Mark this post and the followings unread

pdman1 wrote:
OK with your meter set to the lowest ohm scale measure across D4 with the power Off.
What do you get for a resistance ?


So do you mean cathode to diode on the D4 or does one lead go to ground?

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pdman1



Joined: Mar 28, 2007
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Location: North Shore Massachusetts

PostPosted: Sun Mar 03, 2013 4:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

No not to ground.
Measure across D4. Put one probe on one end of D4 and the other probe on the other end of D4.
Then switch the probes to measure D4 again. What resistance do you measure?
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Gothboy



Joined: Feb 21, 2006
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PostPosted: Mon Mar 04, 2013 4:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

pdman1 wrote:
No not to ground.
Measure across D4. Put one probe on one end of D4 and the other probe on the other end of D4.
Then switch the probes to measure D4 again. What resistance do you measure?


20m setting-0.03 on both

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pdman1



Joined: Mar 28, 2007
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PostPosted: Wed Mar 06, 2013 4:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

You need to use the lowest ohms scale usually 200 or 400 ohms. Sounds like you used the 20 MegOhm scale. Measure again.
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Gothboy



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PostPosted: Thu Mar 07, 2013 10:49 am    Post subject: Reply with quote  Mark this post and the followings unread

pdman1 wrote:
You need to use the lowest ohms scale usually 200 or 400 ohms. Sounds like you used the 20 MegOhm scale. Measure again.


The digital multimeter I'm using has 2k, 20k, 200k, 2M, and 20M settings in the Ohm area of the meter.

I get 0.64 and 0.29 across using 2M

using 200k I get 12.1 and 67.5 across. There is resistance present.

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pdman1



Joined: Mar 28, 2007
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PostPosted: Thu Mar 07, 2013 4:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

Doesn't make sense. You don't get a voltage drop across D4 when measuring voltage. Does you meter have a diode setting? Use this to measure across the diode.

I would desolder what you did and look for open or shorted tracks, pads, etc. Then carefully install your battery holder. Such a simple procedure that is not making sense.
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Gothboy



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PostPosted: Tue Mar 19, 2013 8:38 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm at it again...removed the battery and cleaned up the area on the backside of the board where the battery goes. I'm attaching some photos of the front and back. You can clearly see where the holder goes and the + and - contacts on the front. My question is in regards to the area on the back where the + goes it's a strip on the right(Looks a bit like a landing strip) is the + supposed to be touching this or is it just for solder and the + tip is in the solder?


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pdman1



Joined: Mar 28, 2007
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PostPosted: Wed Mar 20, 2013 5:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

You need to clean up the backside of the PCB. Use 1t least 90% alcohol and an Xacto to scrape off all that gunk.
Also looking at the top component side battery minus terminal, you need to make sure you have continuity between the top pad and the bottom PCB pad. It looks like you may have destroyed the via or feed through of the Pad. This via connects the top pad to the bottom pad.
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Gothboy



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PostPosted: Sun Mar 24, 2013 10:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Cleaned the back of the board, went out and got new rosin core solder. Went at it again and did a re-solder. Still has the same problem so it's off to HiTech I'm afraid. It's apparently just beyond me at this point. Sad Rolling Eyes
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pdman1



Joined: Mar 28, 2007
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PostPosted: Mon Mar 25, 2013 5:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK

as an option, I repair Synths here on the North Shore. I know Lawrence is closer but if they can't do anything let me know.
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planetqwerty



Joined: Jan 17, 2016
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Location: UK

PostPosted: Sun Jan 17, 2016 12:08 pm    Post subject:  Yamaha DX7 Battery replacement issue
Subject description: Might this be the problem, Gothboy?
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According to the YouTube clip titled "YAMAHA DX7 Battery Repair Tips #1" the battery should not be pressed hard against the board, otherwise it'll make contact with other connections. http://youtu.be/uGIaSzyLFb0?t=2m15s

The author suggests that, when soldering it to the board, you use a bit of card as a spacer. I guess it can be removed afterwards.
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markrune



Joined: Oct 23, 2017
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Location: United Kingdom

PostPosted: Mon Oct 23, 2017 8:40 am    Post subject: Help with DX7 Battery Change
Subject description: Any other suggestions
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OK I have been bashing my head against a brick wall on this one. After many years of use my DX7 started loosing its internal memories. Running the battery check it was showing it was at 4.6v , which is good for a 3o+ year old 3 volt battery. So looked like the D4 Diode had gone.

So I replaced with an IN4005 diode, which I was told is a replacement for the original ON95. So new battery holder and battery attached and I get 3.2v from battery to Diode, across diode I get 2.6v and from D4 to IC 19,20and 21 Pin 24 I also get 2.6v Smile so all should be good.

Power on DX7 and get message Check Battery and pressing check function it is showing 0.7V so what is wrong. Do I need a different type of diode or has something else gone amiss ? Please help have been trying to resolve for three days now with no luck

Many thanks in advance if anyone can help
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electrotech



Joined: Apr 24, 2013
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Location: Ayrshire Scotland

PostPosted: Tue Oct 24, 2017 4:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello Mark,

According to the circuit diagram, the original diode used in the DX7 is an OA95. This is a germanium signal diode and is used because it has a low forward voltage drop (~0.2V) compared to a silicon diode (~0.6V).
A 1N4005 is a silicon power rectifier and is not the ideal replacement...
Also, when soldering in germanium devices it's a good idea to use heat sinks on the leads as they are very easily damaged by heat from the soldering iron. (small croc-clips will do)
If you'd like some OA95s send me a PM and I'll send you some in the post.
I'm not that familiar with the DX7, but I would check the 'VB' line (battery voltage) is reaching the part of the circuit that reads the voltage as the in-built voltage check might be faulty.

Hope this helps.

Andy
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markrune



Joined: Oct 23, 2017
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PostPosted: Tue Oct 24, 2017 6:48 am    Post subject: Its the wrong Diode
Subject description: DX7 battery issue
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Andy, thanks for confirming my suspicions, I managed to come to the same conclusion that the Diode was the problem, actually it works as far as memory backup is concerned Smile but when turning on the machine or running the power test, it is not showing the value that is actually being produced , when measured by a volt meter. I have located a couple of Germanium 0A35's on line, so will swap it out once arrived.

I guess for the last 25 years I was under the impression that the battery was better than it actually was, so wont hurt if for a week or so, it looks like there is an issue, when there is not.

This morning was the first morning for several weeks, that I turned on the DX7 and none of the internal memories were corrupted.
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markrune



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PostPosted: Sun Oct 29, 2017 12:13 pm    Post subject: AAAARRRRGGGGGG
Subject description: Check Battery
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OK so I have replaced diode with a germanium OA95 and no difference, all the voltages seem to be right

battery to cathode side of D4 = 3.2V

battery to anode of D4 =2.6v

anode D4 to pin 24 of ICs 19,20,21 = 2.6v


The synth seems to be holding memory but keeps displaying 0.7v on battery check and check battery on power up. Its bloody annoying, but the synth works fine. Also tried a Shoctkey Diode with exactly the same results.

any ideas or suggestions any one
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dearyou666



Joined: Aug 21, 2020
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Location: america

PostPosted: Fri Aug 21, 2020 10:55 am    Post subject:
Subject description: replace battery
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I'm having this issue so i'm going to unearth this post. I'm getting 5v from the internal diagnostic. Memory is corrupt if I leave it off overnight. I haven't taken a look at D4 yet but Markrune/Gothboy if you ever figured it out I'd love to know what happened.
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grantb3



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Posts: 29
Location: USA

PostPosted: Thu Feb 08, 2024 12:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm also having that problem where the battery voltage reads too high, yet there is memory corruption. Not sure I have a replacement germanium that will work. The other possibility, though remote, is that the A/D and Sub CPU are getting the wrong value. One might need to look at that section. I don't see how bad RAM could cause an extra high voltage on the memory test, but I will check out all the avenues.
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