DX7 IID won't power on

rawl747 · Unread post by **rawl747** » Wed Oct 10, 2018 4:56 pm

Diodes are designed to pass current in only one direction. So, they should have a relatively small resistance measured in one direction and a much higher resistance measured in the other. I would not recommend using the 'continuity" mode of a multimeter which it sounds like you are doing if relying on the beeping sound as an indicator of resistance.

And, it is best to lift one end to isolate the diode from other components that might give you a false reading.

purcell · Unread post by **purcell** » Wed Oct 10, 2018 4:58 pm

Did your DX 7 possibly even have an electrical short circuit?
If so, who knows what is broken then?

If nothing works ... ebay (or ebay kleinanzeigen) should help.

You may buy another DX 7?

Example:

https://www.ebay-kleinanzeigen.de/s-yamaha-dx7-ii/k0

Get it - ebay france etc. in france.
-------------------------------------------
Ok! I'm out of here.
That all is "something" for MIKS and other specialists.
Good luck! I hope it works!

djazz75 · Unread post by **djazz75** » Wed Oct 10, 2018 5:21 pm

My PSU is the VB78450 (north european), and I have a D8.

my beep is continuous. My multimeter is a fluke 115. actually, with a correct diode, the beep is very short. but there, according to the manual of the multimeter, with a continuous beep, the diode is in short circuit.

I can already try to change it, we'll see ..

djazz75 · Unread post by **djazz75** » Wed Oct 10, 2018 5:54 pm

purcell wrote: ↑
Wed Oct 10, 2018 4:58 pm

You may buy another DX 7?

yes I also considered the soluton to buy another DX7, if I find that he is doomed.
-------------------------------------------
Ok! I'm out of here.
That all is "something" for MIKS and other specialists.
Good luck! I hope it works!

Unread post by **Miks** » Wed Oct 10, 2018 6:57 pm

djazz75 wrote: ↑
Wed Oct 10, 2018 5:21 pm
My PSU is the VB78450 (north european), and I have a D8.

My spare PSU is the VB78460 (European/W-Germany/Australian Model) which also has the diode D8.

...the diode is in short circuit...

Not mandatory. There may be a capacitor in parallel with the diode which had failed. Did you take out the diode for measuring purposes?

djazz75 · Unread post by **djazz75** » Wed Oct 10, 2018 7:41 pm

I'll take it out of the circuit to test it, I'll let you know

Unread post by **Miks** » Wed Oct 10, 2018 8:09 pm

djazz75 wrote: ↑
Wed Oct 10, 2018 7:41 pm
I'll take it out of the circuit to test it, I'll let you know

Ok, that's fine.

Here's where the 'missing' diode D8 belongs into the schematic
(they've simply forgotten to put it in the drawing...)

: Missing diode D8.jpg (17.25 KiB) Viewed 122 times

If you look onto the (complete) schematic you can see that if one of those parts: R22, C23, C24 will be 'shorted' or has a low resistance your meter will beep continuously...

djazz75 · Unread post by **djazz75** » Wed Oct 10, 2018 8:33 pm

ok, I tested the diode D8 outside the circuit: it is ok. I will test the components around D8.

the schematic you are showing is not in the service manual. can you send it to me ?

rawl747 · Unread post by **rawl747** » Wed Oct 10, 2018 9:01 pm

The schematic is in a separate PDF file in the yates.ca\DX7 FTP site

Unread post by **Miks** » Wed Oct 10, 2018 9:04 pm

@ djazz75: Check your PM's

djazz75 · Unread post by **djazz75** » Wed Oct 10, 2018 10:23 pm

Thanks Miks

this schematic will be useful to me.

djazz75 · Unread post by **djazz75** » Thu Oct 11, 2018 8:54 pm

say, it's normal this coulure at the bottom of the capacitors ?

Unread post by **Miks** » Fri Oct 12, 2018 12:48 am

If you mean that yelloish goo (see arrow) - yes, that's normal. It's a kind of glue used to fasten electronic components to the pcb. No reason to worry...

: Goo.jpg (35.78 KiB) Viewed 74 times

djazz75 · Unread post by **djazz75** » Fri Oct 12, 2018 11:37 am

Ah OK. I suspected it was normal because all PSU photos on the internet have. thank for confirmation.

rawl747 · Unread post by **rawl747** » Sat Oct 13, 2018 5:24 pm

The leakage from bad Electrolytic caps will be a thin almost clear and often sticky liquid. More common to see is the top of the capacitor cylinder bulging upward. The glue you are seeing is as Miks said, normal.

DX7 IID won't power on

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