DX7 IID won't power on

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DX7 IID won't power on

Unread post by djazz75 » Mon Oct 08, 2018 6:26 pm

Hi everybody,

I need your help.

my dx7 IID does not want to put in power anymore. I have not used it for several months, it remained in his flight case, dry, and today, impossible to put it on.

I checked the power button, and it works. how to check the output voltages 12v, -12v, 5V ?

Thanks
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Derek
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Re: DX7 IID won't power on

Unread post by Derek » Mon Oct 08, 2018 7:35 pm

Hi,

If you have no signs of LEDs or LCD activity, I would suspect power first. Not sure where you are, but I would check fuses first, including any in the plug (a feature in the UK). The PSU probably has some as well, and always worth checking, as sometimes fuses can pop for no reason other than old age, or maybe a power surge.

For that you will need a multimeter with a continuity function which you can use to “beep” out the fuses to ensure that they are stil OK.

CAUTION: do not check fuses where powered, and if you do start checking voltages, be aware that there are potentially exposed mains voltages inside the synth. If you have any doubt about your ability to do this without electrocuting yourself, please give the job to an experienced technician. I am lucky in that I had a four year electronics apprenticeship (and a few shocks along the way, that teach you to be more careful ;) ) to give me the confidence to dive into my synths when I feel the need to.

If the fuses are OK, then look for some chunky connections running from the PSU board to the other PCBs (should be obvious) and check with a multimeter set to measuring voltage. Try and measure with the plugs in situ, as some PSUs do not like being unloaded.

I’m not sure what you mean by “trying the power button”. Have you checked it for open circuit when off or short circuit when on, or do you mean you can press it in and out? If the latter, that does not necessarily mean that it has not failed....
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Re: DX7 IID won't power on

Unread post by djazz75 » Tue Oct 09, 2018 11:04 am

Thank Derek.
Yes I am very careful, I myself have already taken shock by intervening on a hammond amp and now I'm very careful.

I checked the button with a multimeter in continuity mode to see if he does his job well when we press it. he works.

the fuse is OK.

what is the procedure to check the output voltages of the psu: +12, -12, +5. ?

it seems that the voltage regulator can also be dead in some cases. how to check it ?
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Re: DX7 IID won't power on

Unread post by Derek » Tue Oct 09, 2018 8:30 pm

I can’t give specifics as I no longer have a DX7II. With your multimeter set to read DC Volts. Put the black lead on an obvious ground point (the case is usually earthed, so a case screw us usually a good point, and then probe the connectors that come from the PSU to the other PCBs. You should see some volts if the PSU is working.

Worst shock I ever had was from a 350V DC PSU in my apprenticeship days. We used to charge capacitors to throw at other apprentices or put in carefully insultated tobacco tins, masuerading as drill bit holders, and one day I slipped.....

That one went all the way up my arm and for years on my left had I had the two marks which matched the spacing of the PSU terminals......
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Re: DX7 IID won't power on

Unread post by djazz75 » Tue Oct 09, 2018 9:02 pm

Whaou it's not a small shock, you were lucky ...

I tested the outputs (with the synth turned On), I have 0v everywhere. is it serious doctor ?


[url=https://goopics.net/i/VQOKZ]Image[/url
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Re: DX7 IID won't power on

Unread post by Derek » Tue Oct 09, 2018 9:07 pm

Sounds like a dead PSU. Are there any internal fuses to check?
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Re: DX7 IID won't power on

Unread post by rawl747 » Tue Oct 09, 2018 9:50 pm

Hey,

If you need schematics and a copy of the DX7II Service Manual look here:

http://yates.ca/dx7/

Rawl
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Re: DX7 IID won't power on

Unread post by djazz75 » Wed Oct 10, 2018 12:14 am

thank you for the schematics links.

Derek, there is only one fuse on the PSU. maybe we should test the voltage regulators ...
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Re: DX7 IID won't power on

Unread post by Miks » Wed Oct 10, 2018 12:51 am

djazz75 wrote:I tested the outputs (with the synth turned On), I have 0v everywhere. is it serious doctor ?
Yes, it IS serious - but it may be cured... 8)

The culprit may be (one of) the electrolytic capacitor(s) C11 (and C12). Since you seem to live in France (where the mains have 230 Volts) you should find both of them (C11 & C12 = 100µF/200V each) fitted on the PSU's pcb. Some of them tend to fail over the years due to agening. But be warned: the capacitors C11 & C12 hold a VERY HIGH VOLTAGE (more than 320 Volts if they're in working order :!: ) If unsure how to proceed leave this job to a tech-savvy person!


My suggestion: replace ALL electrolytic capacitors on the PSU while you're at it! Those capacitors don't cost a fortune but the chances to cure that issue are high imho.

You'll need:..................................My recommendation:

2x 100µF/200V (C11, 12)..................2x 100µF/250V

2x 2200µf/10V (C23, 24)..................2x 2200µf/25V or more

4x 220µf/25V (C19, 20, 21, 22)..........4x 220µf/35V or more

Edit: forgot to mention this little guy:

1x 1µF/50V (C25)..........................same type

Choose a bit higher voltage to be 'on the safe side' so to speak. :wink:
If you go for higher voltages please take care for the 'mechanical' dimensions too - especially the capacitors 'pin' spacings! 8O
My (key related) gear (in alphabetical order):
Ferrofish: B4000+
Kawai: K1 II
Korg: M1 (up'd to EX, w/ 'Cool Blue'), M1REX (w/ 'Cool Blue'), Poly-800
Roland: D-50, D-110, D-550, PG-1000
Yamaha: AW1600, DX7IID (w/ 'Cool Blue'), EX5R, RM50, RX5, SY99 (w/ 'Cool Blue'), TG500, TX-802, YMM2
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Re: DX7 IID won't power on

Unread post by purcell » Wed Oct 10, 2018 12:54 am

"DX7 IID won't power on" put this to Google.

I found this: Yamaha DX7 II power problem ... it wouldn't power up! And still won't!

Answer: This is a known problem in this model synth. The voltage regulator has blown in it.
It needs replacing.

I had the same thing happen to mine about 5 or 6 years after I got it. Get the battery
replaced at the same time.
--------------------------------
I would have the device repaired by a musicstore. Then you are safe!
Must not happen - but can happen!
Think of a possible electric shock. A nightmare! If after your repair (someday?) the housing etc. may be under power.

I hope that's it: The voltage regulator?!?... Do not take a risk! :!:

Good luck!
( When I wrote this here, Miks has already answered you. What I did not know. But no matter.)
Miks : " If unsure how to proceed leave this job to a tech-savvy person!"
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Re: DX7 IID won't power on

Unread post by djazz75 » Wed Oct 10, 2018 2:06 pm

thanks for your advices. I will probably change the capacitors. It's easy to do.

In the meantime, I pointed my multimeter on D8, and it beep continuously in both directions. This diode must be short-circuited. it could be the cause of the breakdown, what do you think ?
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Re: DX7 IID won't power on

Unread post by purcell » Wed Oct 10, 2018 4:10 pm

What I think?
Buy something new - or used!

For the DX there is
Yamaha Reface DX now!
(Only 3 octaves....bur also only 315 € new!)

https://www.musicstore.de/de_DE/EUR/Yam ... gJYzfD_BwE

Or buy the MODX 6 (has also FM Synthesis!), or MOXF6 etc.

Or let your DX7 IID - professional - repair! ... for 50 €? Then you are safe ... and peace is.
This is only my opinion. You have to decide alone.

If you repair it yourself ... a lot of success and Good luck!
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Re: DX7 IID won't power on

Unread post by djazz75 » Wed Oct 10, 2018 4:40 pm

thank you. I do not need a buying advice, I have everything I need at home ! I just want to repair my DX7.

of course, if I can not, I will go to a repairer, I know many ! but I prefer in a short time to try to depanate it myself.
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Re: DX7 IID won't power on

Unread post by djazz75 » Wed Oct 10, 2018 4:46 pm

In any case it's true that the reface are great, I have the CP reface and it sounds great !

but I'd rather play on the original instruments.
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Miks
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Re: DX7 IID won't power on

Unread post by Miks » Wed Oct 10, 2018 4:49 pm

djazz75 wrote:
Wed Oct 10, 2018 2:06 pm
In the meantime, I pointed my multimeter on D8, and it beep continuously in both directions. This diode must be short-circuited. it could be the cause of the breakdown, what do you think ?
Hmmm - not easy to judge :?

But what puzzles me most is the fact that there's no D8 in the PSU's schematics 8O

Best to test diodes is to 'lift' one leg off the pcb (if practicable) and measure them with the meter set to 'Diode Test' function like shown in this picture:

viewtopic.php?t=11150&p=66055#p66055

The meter should show something like 220, 370, 411 or so in one direction and a much higher value like 1192 (eventually ) or so in the other direction... (these values are only examples).

I tried to measure D8 on a spare PSU that I have at hand and the meter 'beeps' in both directions - but always only for a short moment, then the 'beep' stops.

PS: edited my above post... :wink:
My (key related) gear (in alphabetical order):
Ferrofish: B4000+
Kawai: K1 II
Korg: M1 (up'd to EX, w/ 'Cool Blue'), M1REX (w/ 'Cool Blue'), Poly-800
Roland: D-50, D-110, D-550, PG-1000
Yamaha: AW1600, DX7IID (w/ 'Cool Blue'), EX5R, RM50, RX5, SY99 (w/ 'Cool Blue'), TG500, TX-802, YMM2
Sector101: SYEMB05 (5x), SYEMB06 (3x), EXFLM2 (1kit), MCD Sweet16 (1x), WaveBlade 8MB Card (1x) & 1x Programmer Unit for WaveBlade
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