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ScruffieMember
Can’t help much until you have a supply voltage but yes, it’s either the 741 or transistor in the regulator circuit.
Will need a full set of voltages once it’s going.
ScruffieMemberI think it switched back and forth, there is no set date. Once again, EHX liked to mix things up.
ScruffieMemberThanks (yeah that attachment limit is annoying, you have to host off-site) looks pretty standard, the black plastic DC jacks did come in later in its run.
I don’t know too much about the Broadway Computer Corporation era, I know they owned the name post ’84 but I still wouldn’t like to comment on that pot being original or replacement.
But, as I said, it’s just a paint job variant, EHX did that sometimes… perhaps it was literally a case of a shortage of black ink.
ScruffieMemberNeat! Not seen a paint variant like that.
EHX did vary their silk screenings from time to time, sometimes with different styles, sometimes different paint colours.
The interesting part might be the pot date, by ’84 EHX was out of business so unless it’s a replacement part (plausible), this must have been sold by the Broadway Computer Corporation.
Got a shot of the internals?
September 11, 2020 at 3:23 pm in reply to: Hey all, new here and I’ve got a burning question… #126422ScruffieMemberLooks like the SKB only puts out 100mA and the Cathedral requires 163mA so sounds like it’s likely the issue.
Most high quality digital effects are going to require more than 100mA.
ScruffieMemberAs in the Mini Synth with Delay? I’ve never seen any mention of a schematic floating around.
Do you have one for repair or something? If you can take some photos of the inside it might be possible to work out if the delay circuit matches up to any other EHX product.
ScruffieMemberThe switch inside takes care of changing the circuits operation from 9V to 18V with a voltage booster (charge pump) circuit.
Only use a 9.6DC-200 supply with it.
ScruffieMemberLate 90’s, early 00’s.
ScruffieMemberYou have to look at the back of the pots to date it with any sort of accuracy but that’s a 70s/80’s model, not a 90’s reissue.
ScruffieMemberThe output voltage should change with the input bias, go back to checking the solder joints etc. and then I’m afraid it’s probably a dead SAD if that doesn’t help.
Your scope should show a square wave on pins 10 & 11 of the 4047 and a square on one output pin of the 358, a triangle on the other.
ScruffieMemberZero effect from the trim pot? So does it not alter the bias voltage on the input of the SAD?
Hmm, if the tantalum/electrolytic caps are good and you’ve tried replacing the 358 and the pot, besides bad solder joints you’d have to start looking at faulty resistors or non-polarized capacitors, not impossible but a rare occurrence. It can be helpful to check for continuity between pot and its connections for broken solder traces.
I take it you don’t have a scope?
ScruffieMember4558 & 4047 voltages look good but yes there is a problem with your LM358, it should have varying voltages on its output pins.
Have you checked the tantalum capacitor between pins 1 & 2? Also the solder joints on the rate pot, they often break.
But… your SAD voltages certainly aren’t good, output DC that low could certainly imply it’s kaput… have you checked the bias and the solder joints? On rare occasion poor connection with the socket can be to blame too so its worth cleaning them.
ScruffieMemberCould you remove the circuit board and post a photo of the component side please?
There was an early power regulation circuit which was later revised due to problems, you might need to send it to a tech to have that done for you.
A correct polarity 18V supply shouldn’t have hurt it… are you sure the EHX supply wasn’t already centre positive and your adapter cable didn’t actually switch it to centre negative?
Dark marks near the switch is probably just solder flux and nothing to worry about.
ScruffieMemberHard to say with certainty without having it in hand to test, could just be a loose solder joint but it probably needs the electrolytic & tantalum capacitors replacing at this point in its life, their failure in several places in the circuit could lead to the described symptoms.
ScruffieMemberSorry I can’t give a more definitive answer! Just one of ‘those’ problems. But if there is a more obvious problem down the line or after a while you decide it definitely doesn’t feel right, it’s a £0.25 chip and a 15 minute job to replace it. Can walk you through it as long as you’ve got a soldering iron.
With a couple of diodes you can tack some protection on the back of the circuit board if you wanna do it safely in future too.
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