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Prophet 600

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Re: Prophet 600

Postby nickle15 » Sun Mar 14, 2021 8:05 pm

Hugh Robjohns wrote:Good work on tracking downthe failed chip, and nice to know our collective hypothesising identified the likely culprit. Fingers crossed the replacement process goes smoothly.

Yes you guys definitely deserve a diagnosis fee - unfortunately all I can say is thanks!!

We desoldered about half of the pins yesterday just to get a little work knocked out. First time for me with a soldering pencil. Not the last though! We're supposed to have the part by the 22nd at the latest.

I'll keep you all posted, and again, thanks for the help!
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Re: Prophet 600

Postby nickle15 » Mon Mar 22, 2021 3:07 am

We got the chip replaced tonight. In the process of removing the old chip there were three traces that came loose so we made jumpers for those three after we put the new chip in place.

Powered the keyboard up, selected a preset and pressed a key. Nothing. Plugged in a MIDI keyboard to see if MIDI would work. Nothing.

We checked to make sure power was getting to all the right places and it appears to be.

Wednesday night is our next work session and again, I'll keep everyone posted. I'm sure dad has some ideas of things to try when we get together but if anyone has anything they want to suggest we check that would be great. Thanks!
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Re: Prophet 600

Postby Eddy Deegan » Mon Mar 22, 2021 3:21 am

Nothing to add on the technical front but if I've learned anything in a half a century of problem solving of one kind or another, persistence is 90% or more of the game in any situation.

Keep at it and I look forward to a future update containing the word "eurkea"!

Good luck and don't give up!
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Re: Prophet 600

Postby nickle15 » Mon Mar 22, 2021 3:27 am

Eddy Deegan wrote:Nothing to add on the technical front but if I've learned anything in a half a century of problem solving of one kind or another, persistence is 90% or more of the game in any situation.

Keep at it and I look forward to a future update containing the word "eurkea"!

Good luck and don't give up!

Thanks for the encouragement. Tonight was frustrating but I’m convinced we will indeed have that “eureka” moment. And I’ll be glad to share it when it happens!
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Re: Prophet 600

Postby nickle15 » Thu Mar 25, 2021 1:46 pm

So we got another solid 2.5 hours of work last night. The good news is that everything we checked has correct voltages running to it. Everything "works", except no sound (and one new issue outlined below). I can't remember the name/type of chip but there's a 14 pin chip that has different frequencies running out of it and all of those checked out ok with the oscilloscope. The last part we tried to check was the actual audio output and had some trouble with the scope. So today dad will be following up with the scope and making sure we were using it correctly. That's a new item for him (though he used one back in the day).

One thing I noticed was that with the keyboard turned all the way up, and the very small Dell computer speaker we plugged into it also turned all the way up, the "noise" I can hear when the speaker is held up by my ear changes a bit as I switch switches on the keyboard. Also, if I start the arpeggiator I hear "noise" changes at regular intervals. So it seems like something is happening.

The new fault we found last night was that the membrane pad no longer works when we press the 1, 2, 3, and 0 keys, and there are a few of the function buttons that don't light up also. AND the LCD display is missing the very bottom row of lights. So the number 8 looks like a capital A.

The weekend before we started troubleshooting my friend (who is the actual owner) wanted the Gligli mod installed. Since there is no soldering required I performed that operation on my own and the keyboard worked as expected afterwards. But given my unfamiliarity with the new control scheme with Gligli I'm considering putting the factory chip back in for now while we continue to troubleshoot.

So, there's the update. We've not had any victories yet and keep taking steps back it seems, but we're not discouraged yet and will get back in there this evening. As always if anything I've mentioned sparks an idea please feel free to share.
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Re: Prophet 600

Postby blinddrew » Thu Mar 25, 2021 4:13 pm

nickle15 wrote:We've not had any victories yet and keep taking steps back it seems, but we're not discouraged yet and will get back in there this evening. As always if anything I've mentioned sparks an idea please feel free to share.
You're not taking steps back, you're just finding the right step forward! :thumbup:
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Re: Prophet 600

Postby nickle15 » Thu Mar 25, 2021 4:45 pm

blinddrew wrote:
nickle15 wrote:We've not had any victories yet and keep taking steps back it seems, but we're not discouraged yet and will get back in there this evening. As always if anything I've mentioned sparks an idea please feel free to share.
You're not taking steps back, you're just finding the right step forward! :thumbup:

Thanks - that's certainly how I'm viewing it! :D
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Re: Prophet 600

Postby Hugh Robjohns » Thu Mar 25, 2021 4:52 pm

You are taking the appropriate anti-static precautions when working on the innards of this thing aren't you?
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Re: Prophet 600

Postby Folderol » Thu Mar 25, 2021 4:59 pm

The display missing the bottom line is most likely to be caused be a broken connection on one strand of a ribbon cable from it to the rest of the unit.
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Re: Prophet 600

Postby nickle15 » Thu Mar 25, 2021 5:19 pm

Hugh Robjohns wrote:You are taking the appropriate anti-static precautions when working on the innards of this thing aren't you?

Yes. :)
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Re: Prophet 600

Postby nickle15 » Thu Mar 25, 2021 5:20 pm

Folderol wrote:The display missing the bottom line is most likely to be caused be a broken connection on one strand of a ribbon cable from it to the rest of the unit.

I'll take a look tonight. If I remember correctly the LED display itself is directly connected to one of the boards - but again, I'll look more closely this evening. Thanks for the tip!
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Re: Prophet 600

Postby jjlonbass » Thu Mar 25, 2021 5:32 pm

Do both 7 segment displays have the bottom segment off?
Does the "ARP ASSIGN" LED light up?

It's worth checking your soldering around the replaced 4514 very carefully - there may be a solder bridge between 2 or more pins of this IC. An illuminated magnifier is very useful for these checks.

John
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Re: Prophet 600

Postby nickle15 » Thu Mar 25, 2021 5:46 pm

jjlonbass wrote:Do both 7 segment displays have the bottom segment off?
Does the "ARP ASSIGN" LED light up?

It's worth checking your soldering around the replaced 4514 very carefully - there may be a solder bridge between 2 or more pins of this IC. An illuminated magnifier is very useful for these checks.

John

Good idea - we'll double check the soldering tonight.

There were a few LED lights that wouldn't light, but I didn't write them down. Part of the reason is that the Gligli mod changes some behaviour on the keyboard so I didn't know for sure what to expect. I plan to reinstall the original chip to restore factory behavior for more reliable troubleshooting.

And yes, both 7 segment displays are missing the bottom segment.
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Re: Prophet 600

Postby jjlonbass » Thu Mar 25, 2021 5:59 pm

A short between pins 22 (D3) and 23 (I) of the 4514 could cause the bottom segment of the displays and "ARP ASSIGN" to be stuck off. Similarly a short between pins 10 (S2) and 11 (S0) or between pins 11 (S0) and 12 (Vss) would affect keypad buttons 0 to 7.
Other combinations are possible!

John
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Re: Prophet 600

Postby Hugh Robjohns » Thu Mar 25, 2021 6:03 pm

Its probably self-evident that these new faults will undoubtedly be the result of your difficulties with lifted tracks around the replaced chip, so lots of careful scrutiny around those tracks and the new links added to replace them will be required.

Glad to hear about the static precautions.
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