Deltalab Effectrons - help needed with repair & sourcing 4-terminal centre-tapped pots

[pvision]

I have a stack of Effectrons that either don't pass signal or pass signal with no delay. Typical faults with these are broken centre-tap pots and I have so far drawn a blank sourcing replacements. I'll follow up this post with specs of the pots

Before I order a box full of CMOS and rare ram chips, is there anyone in the UK who would claim to be an expert with these? If there is no-one I will break out the scope and get testing but I think it may be a long process!

I am based in Brighton, UK

Thanks

 

[pvision]

I believe the way the output pot works is that the output comes from the wiper, the centre tap is fed with the dry signal and the two ends of the pot are fed phase & antiphase delayed signals. So there's no real alternative to a 4-terminal pot unless I change the way the circuit works

 

[Rob Flinn]

I believe the way the output pot works is that the output comes from the wiper, the centre tap is fed with the clean signal and the two ends of the pot are fed phase & antiphase delayed signals. So there's no real alternative to a 4-terminal pot unless I change the way the circuit works

Is there no way to use a dual pot to replicate this ? Feeding each wafer from either side ?

 

[JohnRoberts]

You might be able to rig up a 12 position switch to mimic the tapped pot...

JR

 

[pvision]

Good question. I can't see a way. There are three signals and I can't see a way of getting one signal only from two pots

There's probably a way of doing this using a truth table but my A Level maths is long behind me!

 

[pvision]

12 position switch is a good call. The other is to just have an inphase / dry blend and ditch the antiphase signal

 

[emrr]

12 position switch is a good call. The other is to just have an inphase / dry blend and ditch the antiphase signal

Or hack in a phase switch?

 

[pvision]

Or hack in a phase switch? - I thought of that but don't really like to modify front panels

Finding pots to replace those in vintage gear is getting hard and this one may be impossible

 

[emrr]

I have a DL-4 with intermittent input, I know every time I open it to contemplate replacing the pot I close the lid pretty quickly.

 

[pvision]

There's a company in Germany that will make custom pots but their 4-terminal pot has the wrong pin setup for the Effectron. Not the end of the world to to wire the pot off-board but it would be nice to find a drop-in replacement

 

[Monte McGuire]

I have worked on a few Effectrons and it's worth examining the solder connections - many units with faults had 100% good pots with faulty solder joints. The PCBs were wave soldered and generally good, but the pots were installed by hand by some poorly skilled technicians. Of course, now that decades have passed, the unwetted parts of the solder tags on the pots are now even harder to wet, so maybe a wire brush and some other remedy will be needed to get a reliable connection. Still, in every case I've dealt with, it was a bad solder joint, and not a bad pot with old Effectrons. Also suspect are the I/O jacks, for the same reasons.

 

[NOON]

I've repaired a few Effectrons that had a multitude of niggly issues that mostly went away with replacement of the electrolytics. One was a broken pot but fortunately not the centre tapped one.

 

[pvision]

Thanks for the info. Pots & jacks are definitely top of the list for faults

In most cases the bad examples I have pass signal but don't produce any delay output. I've checked voltage rails & recapped the power supplies in all of them so I think I need to tackle the digital side now

I am a bit suspicious of the delay time selector switches as well...

 

[Rob Storms]

I fixed a friends Effectron after he got a couple center tapped pots from Syntaur.com ( looks to me they dont have them any more but you could check. I ran in to some interesting problems so i am reproducing the email I sent to Syntaur after the repair was completed."Hello! Thought you might be interested. A friend got two pots from you folks ( your Part #3750 ) and we set about replacing the mix pot in his effectron ( the pot was an exact replacement except for threaded bushing size). The fault with the old one was that the lugs on the pot made no or intermittent connection with the resistive tracks they were supposed to be connected to. We verified this by actually checking continuity from the lug to track ( carbon I guess) while the old pot was out of circuit. I always thought this happened because near invisible cracks developed in the track( at the rivet) due to the pot moving in relation to the PC board ( usually due to the front plate mounting screws getting loose and allowing this). We installed the new pot and the dry mix was available only if we flexed the new pot lightly rearward. We bypassed any suspicious looking PCB lugs or connections. We finally traced the problem to the same connection issue between the pot lugs and the tracks( via the rivet). With a pointed object through the rivet holes and gentle prying ( and some Deoxit applied to the rivet/lug/track connection) I was able to make the problem go away ( we did all this while monitoring dry and effected signals). What I THINK happened is that tiny movement of the rivet ( or the lug) relative to the track scraped through some possible corrosion ( or contaminant) preventing a solid connection. We ended up mounting the second replacement pot he received with the lugs in the air and connected to the PCB via wires. Works fine and the 2nd pot does not exhibit the problem that we found with the first. Thought you might appreciate the story! Best to all at that end, Rob Storms"

 

[pvision]

Thanks for the info, Rob. I've read elsewhere that pot failures are often caused by the unit being dropped and shock from the knobs hitting the ground smashes the pots, or breaks the solder joints, internally

I can verify this - I had $1000-worth of gear shipped from the US (with front panels facing downwards), dropped, and 60-70% of the pots broke. Unobtanium parts, naturally. No visible damage from the outside, sender refused claim