JX-8P Displays "Roland JX-8P 12"

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Tiltrelia
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JX-8P Displays "Roland JX-8P 12"

Post by Tiltrelia » Tue Sep 17, 2019 12:39 am

After transporting my JX-8P home, it just hangs on the "Roland JX-8P 12" screen. I opened it up to check the power supply and I am getting some interesting voltages. The 5v and -5v rails are reading correctly, however the 15v rail is reading +/- 6v and increases to 9v then drops to 5v, this continues. The longer I leave it on the more I begin to smell burning electronics. When I disconnect all cables from the power supply and turn it on the voltage increases on the 15v rail to about 24v and stays there. I am assuming IC1 (M5230L) is the issue and currently have one on order along with a pair of rectifiers and capacitors. The 5v rail stays the same when all cables are unplugged. Has anyone had any similarly related issues to this?

Rasputin
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Re: JX-8P Displays "Roland JX-8P 12"

Post by Rasputin » Tue Sep 17, 2019 5:45 pm

Tiltrelia wrote:
Tue Sep 17, 2019 12:39 am
After transporting my JX-8P home, it just hangs on the "Roland JX-8P 12" screen. When I disconnect all cables from the power supply and turn it on the voltage increases on the 15v rail to about 24v and stays there.
Never had that issue, but it seems like you're barking up the right tree for this. JX8P is hanging on its self-tuning because of the bad analog rail. Keep testing and making repairs with it unloaded until both the + and - analog rails are sane.

Once the analog rails look fine, briefly test it under load and see if the voltages stay at +/- 15V. If one or both aren't in spec under load then start investigating the mainboard.

Tiltrelia
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Re: JX-8P Displays "Roland JX-8P 12"

Post by Tiltrelia » Thu Sep 19, 2019 2:54 am

UPDATE: I received the capacitors and rectifiers and installed them onto my power supply, same problem. I left the JX on for a minute and found the source of the smell, Q4, a transistor that runs on the 15v rail ON THE LOGIC BOARD blew up. This is the first transistor for the whole synth, so no wonder it was freezing up. I will post an update once I receive the replacement

Tiltrelia
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Re: JX-8P Displays "Roland JX-8P 12"

Post by Tiltrelia » Fri Sep 20, 2019 9:05 pm

Just revived a new pair of transistors (KSB1366GTU and KSD2058YTU) and put them on the power supply. I am now getting just a bit less that 15V out of it, and it no longer hangs, however I still need another pair for the Logic Board itself because it is now actually succeeding the countdown, it's just extremely slow. The sound output is weak, and I believe all of the analog circuity is not getting enough current. I'll update once I get another pair of transistors.

Tiltrelia
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Re: JX-8P Displays "Roland JX-8P 12"

Post by Tiltrelia » Fri Sep 27, 2019 9:52 pm

Unfortunately anytime I replace Q3 or Q4 they seem to fail instantly. I guess I don't understand what could be causing this to happen. I'm beginning to loose hope for this 8P :(

Tiltrelia
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Re: JX-8P Displays "Roland JX-8P 12"

Post by Tiltrelia » Sun Jan 05, 2020 1:31 am

Good News! This 8P came back to life after replacing D2 and D3, Q3 and Q4. There was also some minor trace damage, and I noticed this board was not identical to the schematic. Oh well, problem solved and all this 8P needs now is a FIP coil for its display.

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