Neotek restoration adventure

[AnalogApples]

Find a Cure for GAS

I bought this old 24 channel Neotek Series III last winter. It had been stored in a garage for 10 years. I got a really great deal on it. Then I discovered that due to the humidity in the garage, the seals on many of the electrolytic capacitors are failing. Mike Stoica told me this is what's happending since it was stored in high humidity. It has many problems which would be explained by having all original capacitors that are failing. Even the IC chip legs have black gunk on them from the moisture.

I've ordered 858 capacitors off of Mouser. Most of those are going obsolete once their stock runs out.

Since I'll be desoldering about 2,000 wires, and resoldering about 2,000 wires, I'm now worried about hysteresis between the capacitor wire and the solder pad. Solder apparently is MUCH less conductive than copper. Which means, if I want to do it right, my capacitor wires must be physically touching the pad while I apply solder. I cannot just feed the capacitors in, and fill in the holes with solder. I think it'll take me much longer to replace all the caps this way, but maximizing wire to copper contact before applying solder is the best way to do it. I'll be literally tugging on the capacitor from one side of the board while I apply solder. I'm going to buy some Cardas audiophile type solder which they claim is best for audio. It's $45 for a 1/2 pound.

Does anyone have any thoughts about this or anecdotes about professional recapping jobs on large consoles? Did you guys just feed the caps through, then solder the hole and clip the wires, relying on the solder to connect the component? Or is it standard to completely clean off the pad, then bend the cap wires to make maximum contact with the pad, then tug on the cap to keep it tight against the pad while adding solder?

More details about the mixer: I have a couple of channels that were in the master section but never reinstalled. I can see piles of river silt sitting on some of the components, and on the meter bridge. I think this thing may have been underwater at one point. It's a new power supply, and 19 out of 24 channels are working. My goal is to recap all 24 channels, and the meter bridge, and see where that gets me. Then I only need 2 more parts to rewire it in it's original configuration (I need the master channel, and the meter select channel) It's been a fun, very rewarding project!

 

[AnalogApples]

I did it! Took about 30 hours of labor. I ended up using Cardas Quad solder, which has much lower resistance than regular solder. (you can stretch out a 5 foot length of Cardas and measure resistance compared to regular solder)

I'm surprised that Mouser didn't get my capacitor order counting correct, shorted me about 25 caps. This job would've been a nightmare if I didn't buy a cheap electric solder sucking station, and a separate auto-feeding solder iron. That auto feeding solder iron is a game changer, just put the tip on the pad and squeeze the trigger! Halfway through the job I actually memorized which pads had capacitors and was able to look at the back of the PCB and whiz through the desoldering. I'm probably going to have dreams about 2.2uf caps for the rest of my life.

Unfortunately this did not rescue my 5 dead channels. The opamps in them test ok, so I'm going to replace the transistors and see if that helps. I haven't tested the audio yet, so I don't know how much audio quality improvement I got. I'll post again after I've listened to the console.

 

[AnalogApples]

Update: I was mistaken. Recapping DID rescue my 5 dead channels. All 24 channels are working! It sounds fine, I don't hear a massive improvement in sound quality. I'm jumping for joy. My 30 hours of labor paid off!

 

[TalismanRich]

It can be quite a pain to remove all those old components. Hopefully the circuit board is high enough quality that the pads stay attached. It really sucks when they start releasing. Some of those lead free solders are tough to deal with. A good flux is absolutely necessary. Watch some of the SMD repair work videos. You have to flood the area first.

So how much difference in resistance did you measure between the Cardas and a standard 63/37 solder over those 5 feet. Then figure out that the difference in resistance over those 0.1mm joint (it should be a straightforward calculation). I bet it will be in the micro ohms!

The difference in melt point between Cardas and a generic 63/37 is 6°C which is nothing that any iron can't handle. The 1 lb roll of Kester 44 63/37 solder I bought so many years ago for about $20 should last me for another 25 years or more! I doubt I'll last that long.

Back when I was building slot car frames, we used silver solder because it was so much stronger than regular solder. You needed a really hot iron. But when the car hits the wall at about 40mph, things tend to break at those weak points!

 

[AnalogApples]

It can be quite a pain to remove all those old components. Hopefully the circuit board is high enough quality that the pads stay attached. It really sucks when they start releasing. Some of those lead free solders are tough to deal with. A good flux is absolutely necessary. Watch some of the SMD repair work videos. You have to flood the area first.

So how much difference in resistance did you measure between the Cardas and a standard 63/37 solder over those 5 feet. Then figure out that the difference in resistance over those 0.1mm joint (it should be a straightforward calculation). I bet it will be in the micro ohms!

The difference in melt point between Cardas and a generic 63/37 is 6°C which is nothing that any iron can't handle. The 1 lb roll of Kester 44 63/37 solder I bought so many years ago for about $20 should last me for another 25 years or more! I doubt I'll last that long.

Back when I was building slot car frames, we used silver solder because it was so much stronger than regular solder. You needed a really hot iron. But when the car hits the wall at about 40mph, things tend to break at those weak points!

I was trying to be really careful with those 50 years old PCBs and I didn't lift any pads. Ike, a Neotek tech, was adamant that anyone desoldering these boards needs a good solder-sucker, so his warning really helped. I did not test the resistance of the solder, I just took the word of someone on another forum who claimed they tested it and there was a different resistance. The Cardas has lead in it. Who knows if it's actually better but Cardas seems reputable and they claim their solder is the best for audio. Huge weight off my shoulders now that I can finally stop troubleshooting those 5 dead channels!

 

[TalismanRich]

Of course they claim it's the best for audio. Their business is selling tweaks to hifi folks for big money. Cables, connectors, magic wood blocks to lift your cables off the carpet. I like their musically neutral USB cables. I didn't know 1s and 0s could be amusical.

If you've still got 5 or 10ft of solder, give it a measure, and I'll do the same with my generic Kester solder. I'm interested in how much it differs. I'm not saying it isn't good solder, but that some of their claims border on the miraculous.

But the point is, resistance is proportional to the length of wire and any proper solder joint is a fraction of a mm in length. If solder resistance was a serious problem, it would have been addressed decades ago. The only reason we have the new lead free solders is environmental. Lead is a regulated metal because it's toxic. If you're trying to sell a RHOS compliant item, you have to control what goes into it.

 

[ecc83]

Yes, any idea that solder, be it lead or Pb free adds any significant resistance to a joint in a PCB setup is bllx worthy of the Russ Andrews clan. FFC! Mic cables are BURIED in a "bucket" of solder in every XLR plug! If solder resistance was ever a problem it would show up in speaker circuits which can be 4 Ohms. Never has.

I am always a bit worried when folks go in for such a "mass re-capping"? I always hope they have the equipment and knowledge to check the frequency response and distortion performance post caps?

There is little doubt that in this specific case the caps and other components needed to be replaced but that is not by any means always so. Electro-caps last a lot longer than folks seem to think, 30 years is by no means too old. Check the LF response (against original specifications of course!) before diving in.

There is some benefit in increasing the value of some coupling caps. Not to give a lower turnover frequency but to reduce distortion at LF. Modern equipment has THD figures several orders below those of the days of tape and so improved figures would seem a good idea? Also, since modern capacitors are much smaller now for a given uF/V some areas might benefit from 105C components?

Dave.