Help identifying vintage phaser circuit boards

[VintageGear]

Hi!
I bought a non-working Coron phaser,.... or so I thought. It indeed is not giving any sound, but when opening the pedal, I find two PCBs inside. The little daughter board (labeled EF) contains a 4011 and 4007 which seems to address the switching. The main board is labeled PH-3 (no, not a Boss) and has a RC3403, 4011 and 4558 on it. Also, they might have been replaced.
I never seen these boards before. Any clue on where they came off from? Any detectives here? :-)

[garcho]

I bought a non-working Coron phaser,.... or so I thought

What makes you think this isn't a Coron phaser?

I never seen these boards before

Does that mean you have seen many Coron phaser boards?

[ElectricDruid]

Good questions.

[Rob Strand]

You haven't posted pics of the front:
- 3 knob, centre knob offset
- simple push button with solid-state switching

I'm seeing a possibility as a Coron DC-803.
(Other three knob phasers
Probably not Coron P400 - LED in wrong place,
Probably not Coron DC-804 - 8 stages and our ckt is 4 stages.)

The ideal thing would be to find a schematic.  I'm not aware of any.  There's a *very* small chance it's a copy of another phaser and you might find schematic for the copy.

You could carefully mark the position of the trimpot and try to tweak it so see if it comes back to life.   I try to advise against that as a "magic fix" since you upset the factory settings.   Best to trace the signals a bit:
- Is power getting to the boards?
- Does the LED toggle with the switch?
- Can you see any signals toggling with the switch?
- Is there any audio in bypass mode?
- Starting at the input, at what point in the circuit does the audio stop?
- Is there any audio getting to the boards at all?

It could the a bad socket, switch.   Sometimes CMOS 4000 gates fry.   

It's highly likely one the CMOS gates is used as the variable resistors, instead of JFET.   That chip will not have normal voltages on in as it the gate is wired completely differently to a logic gate (perhaps not even being wired to power at all).   If you want find a schematic of another pedal that's going to narrow it down quite a bit.   Something like the Pearl phaser.

The 4007 could be used as MOSFET audio switch.

It can also be bad electrolytic caps.  However without doing some basic debugging, replacing the caps can be another "magic fix" which doesn't actually fix it.

If the CD4007 is used as the audio switch that leaves the CD4011B as the variable resistors for the phaser.    I'm not aware of the CD4011B being used for variable resistors on any schematic.  In fact I'm not sure it would work at all.

[EDIT: Maybe not, see below]
At this point I'm thinking someone has replaced the chips and that RCA CD4011B is the wrong part.   More likely to be a CD4069UB or something along those lines since that chip can be used as a variable resistor.   You would need to trace the circuit to see which CMOS gate matched up with the circuit - only a few choices really.

It does look like the ICs have been replaced.  Lots of flux on the IC pins.

Interestingly one of the Peal Phasers is a model PH-03!
https://www.experimentalistsanonymous.com/diy/Schematics/Phasers/Pearl%20Phaser.gif

The PCB for this unit often shown as single PCB but that doesn't mean there wasn't a two pcb version.

IC4 is marked as exclusive but I remember it was really a CD4069UB or something.

[EDIT: At this point, CD4011's on both boards could correct]
Unfortunately the Peal PH-03 schematic doesn't use any CD4011's.    However it could yet another case of the wrong IC being put there on the switching boards.  Maybe the Toshiba CD4011 on the switching board is just a quad opamp.   Tracing the circuit and identifying the power pins might help.   When I looked at the PCB it looks like it should be a CD4011 more than an opamp - so maybe the switching flip-flop is the CD4011 and the switch is the CD4007.   All OK but a little different to the Pearl schematic.

It seems this is a different design to the Pearl PH-03.   I traced some of the PCB around the RCA CD4011BF on the main board and the traces line-up with the CD4011 pin out.

I haven't gone far enough to trace the whole schematic but at this point it's probably a circuit like the Ampeg Phazzer except with a CD4011 instead of a CD4069.

If that is the case then the RCA CD4011BF may or may not be correct.   I would expect the CD4011 to at least be an unbuffered part,  some sort of CD4011UB.  It's not a common part but I think you can get them.   The chances of the buffered CD4011BF working would be slim.

In summary of all of the above:  Assuming all the IC's are working.   The most likely issue is the CD4011BF should be an unbuffered CD4011UB.

However, if the unit is not bypassing signal then perhaps one of the chips does have a fault.  It would be wise to fix that first.

[Rob Strand]

I don't know if this helps or hinders but this Phaser has very similar parts choices to the Coron,


The schematic won't be exact but might be useful as a rough guide.   Some areas of difference would be:
- Different resistor and chip numbers: U1 on the schematic might be U3 on the PCB.
- For multi-part chips like opamps and gates different parts of the chip might be used for a given area of circuit.
  For example the schematic uses opamp U1A but the board used opamp U3B; that means different pins as well.
- Part value differences.  I'm pretty sure the 820k's on around U4 on the schematic are 1M on the PCB.
  Also the 33nF (0.033uF) on the schematic are 47nF (0.047uF) on the PCB.
  Resistor R26 on the schematic looks like 3M3 on the PCB.

There will be heaps of stuff like this.  You will have to translate.  Perhaps mark-up the schematic.

Something else.  The PCB has a PNP transistor.  I suspect the transistor is used for the output mixer, like the MXR phaser, whereas the schematic shows a resistive mixer.

[VintageGear]

Hi all! Thanks for all the input!

I bought a non-working Coron phaser,.... or so I thought

What makes you think this isn't a Coron phaser?

I never seen these boards before

Does that mean you have seen many Coron phaser boards?

I was assuming it were not original boards due to the fact the wires were resoldered and it did not fit properly inside the case. Also the daughter board for the switching I did not expect at first glance. There are no mounting holes and they just float around in the enclosure. Did not seem right. The other Coron phaser I had was with the PCB mounted jacks (looks a bit like a phase 90 with top mounted jacks). But I agree, it might be original. It was repaired earlier, and that put me off a bit. The wires were not soldered right. But yes it might be original after all.... Going to investigate a bit further :-)

The 4007 on the daughter board is used for switching the LED and the audio paths. It was dead. Along with the 8-stage opamps (replaced with a TL074 as it has the same pinout). And the input ic buffer was defective. All in all, basically had to replace half the ICs, but now it is up and running again and sounding great!!
Thanks for the schematics Rob! Together with an audioprobe, it was a breeze to fix.

[garcho]

the wires were resoldered and it did not fit properly inside the case... It was repaired earlier, and that put me off a bit. The wires were not soldered right.

You had your work cut out for you! Bravo, great to hear you got it up and running. As R.G. would say, maybe it was someone with a bad case of the BUMS (Blind Urge to Mod Syndrome).

[Rob Strand]

The 4007 on the daughter board is used for switching the LED and the audio paths. It was dead. Along with the 8-stage opamps (replaced with a TL074 as it has the same pinout). And the input ic buffer was defective. All in all, basically had to replace half the ICs, but now it is up and running again and sounding great!!
Thanks for the schematics Rob! Together with an audioprobe, it was a breeze to fix.

Yeah, very cool to get that going.

Very interesting that the apparently buffered CD4011 works as MOSFETs!!