Prophet 5 Rev 3 All Lights Illuminated No Sound

[Script]

If shorted Tantalum cap (yellow, orange), then easy to verify. Power rail to ground is basically open (connectivity beep on multimeter). Any resistor in direct parallel (but which ones are they?) will show no reading.

Then test across cap leads, if open, cut a lead of the cap, can replace cap later.

All with PSU disconnected.

Likely it still needs new regulators.

 

[Khron]

Power rail to ground is basically open

* short-circuited

 

[dr_ew]

Some of the logic on the mainboard needs +12v, the VCO's need -5v.

Not a lot will happen without these.

This is a Rev 3.3 with midi. Turns out my power supply voltages aren't too far off.

-5v should be -22v (i'm getting -28v)
+12v should be +22v (i'm getting +28v)
+5 should be +5.6v (i'm getting +8v)

 

[NoisyIndividual]

This is a Rev 3.3 with midi. Turns out my power supply voltages aren't too far off.

-5v should be -22v (i'm getting -28v)
+12v should be +22v (i'm getting +28v)
+5 should be +5.6v (i'm getting +8v)

Where are you getting this info?

 

[dr_ew]

Where are you getting this info?

There is mention of +22v in section 11-3 of the technical manual where there are notes on upgrade modifications. The technical manual doesn't mention MIDI. I think these voltages are necessary when adding MIDI circuitry. I also noticed that every aftermarket power supply for Rev 3.3 had these voltages. Not a lot of info available out there, but +22v replaces +12v, -22v replaces -5v, and +5.6v replaces +5v.

https://techsmechsvintagesynth.com/products/propsu-prophet-5-power-supply-replacement-kit
https://docs.google.com/document/d/1olmzhuE4bfqXRJobXNkggVSnp6pvY1Nj50o40Ia4B3o/edit?tab=t.0

https://www.ebay.com/itm/155225729924

 

[NoisyIndividual]

So what exactly is the history of this Prophet?
Is it a factory fitted MIDI or a Kenton retrofit etc?
Has someone replaced the power supply with an aftermarket one, have they done it properly or have they supplied -22v to the EPROMS and fried them?

What else are you not telling us?