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Old July 12th, 2014, 12:29 PM   #1
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Sound devices sd-302 mixer

I recently bought one of these mixers used.

A known issue was a faulty LED chain in the levels indicator On checking the appliance there was another intermittent fault evident which may have been known to the vendor or may have been introduced by mechanical shocks during shipping. It does happen.

This second fault was failure to initiate after power on with all LEDs being apparently massively overdriven, possibly why the display had gone faulty in the first place. Normally the SD-302 LED chain exhibits a sweep illumination and it is ready to go. This fault seemed to be temperature related, sometimes an indicator of mechanical shock damage.

The mike channels one and three were also periodically noisy when phantom power was selected.

I opened the unit to see if anything was mechanically damaged that might provoke a total demise. I discovered apparent entry of a small amount of saltwater and particles which appeared to be fine windblown sand.

Given the price I had paid and that there was possible salt damage I did not send it off for a quote as it is not economically feasable and besides that, I am not all that flush with funds.

I did a check and clean through and things improved. However the phantom power noise remained on channel one. The LED chain remains faulty. There are dead LEDs.

I opened it again and gave everything another clean over with jeweller's loupes on my face this time for a much closer look and found small patches of rime in the area of the phantom power circuits I had missed.

It tested fine second time round except again for the LED chain which requires parts to be replaced.

There is initial noise when the mixer is powered on and it takes about 15 to 30 seconds to settle.

According to the SD site FAQ, there is normally initial noise after power on which goes away after levels are adjusted. This also seems to be temperature and time affected. On subsequent power on, the noise settles faster or not apparent if powered on soon after shut down.

Otherwise the recovered audio is clean and comparable to the Mix-Pre through the headphones and passes to the camera-recorder cleanly.

My enquiry of members therefore is whether anyone can tell me what the normal behaviour of the SD-302 is after power-on. I do not have another close-handy to compare.

I must say that I am impressed with the overall build quality inside the device. Conductive paths on the rear surfaces of the PCBs are encapsulated with clear soft silicon. This has gone a long way towards protecting the innards from more extensive corrosion damage.

Any advice will be appreciated.


Why go through all the grief of fixing and mending? It is something I do and in this instance, cost has an influence.

Last edited by Bob Hart; July 13th, 2014 at 02:07 AM. Reason: errors
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Old July 12th, 2014, 05:43 PM   #2
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Re: Sound devices sd-302 mixer

I would suspect salt water damage opposed to mechanical shock. They're almost as rugged as a 58.. Call SD, the good folks there will certainly tell you if there's any end-user procedures.. like a software reset, which I assume you already investigated.. but based on the symptoms, a return to the mother-ship is warranted.. like it or not.
Short term noise on power-up is a common occurrence on some.
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Old July 13th, 2014, 02:19 AM   #3
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Re: Sound devices sd-302 mixer

Thanks for your reply Rick.


I have emailed SD and their rep was very courteous and helpful. They understandably do not encourage user-servicing of their mixers and like yourself, recommend it travels home or to the Australian reseller for check/repair.

For now, I'll see how it travels as it seems to be fine now. I gave it about three hours of continuous run time last night and was fine again today after the initial settling down. This noise is apparently attributed to capacitors charging after power-on.

It is not mission-critical as I have a new-bought Mix-Pre for two-channel camera audio. A three-channel mixer is perfect for a Decca-tree rig I made up for an orchestra recording a few years back. It would have been handy for a couple of events gigs I have had since. These have not been actual earners so the pay-out for new gear just to cover them is not justified.
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Old July 13th, 2014, 12:58 PM   #4
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Re: Sound devices sd-302 mixer

I've had mine for more than 5 years and have never had any issue with it at power up. It just works the way I expect it to. The LED's do their sweep and all is well. Re noise at start up I've never noticed any, but I've never looked for it and always get right to level adjustment after powering up. I mostly record classical concerts so once it's switched on it just runs for a couple of hours which means really low power on /off cycles.

It also means it's always used on a desk in a clean environment and not in a mixer bag being bounced about and exposed to the elements.
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Old July 14th, 2014, 03:06 AM   #5
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Re: Sound devices sd-302 mixer

Jim.

Thanks for your response. The case on this one is a bit polished to bare-metal on the corners so has apparently been used agile. It is less apparently worn than my Mix-Pre. It came with a new Portabrace satchel and was a good deal given the mixer's described state.

Since my last test, it seems to have settled down. Maybe there was a bit of residual damp under a transformer or something else close-fitted to the PCB remaining from my cleaning efforts.

That process was arduous detail mopping with artbrush and distilled water to dissolve and carry away the apparent salts, another detail mopping with another artbrush with methylated spirits to pull the water, wicking out any moisture from tight gaps with paper corners, a blow out with the straw of a can of lens air, then a good period in a dry environment.

A more accepted practice is apparently to remove parts like transformers, coils, crystal cans which might be damaged by water and for the remaining entire board to be submerged in a solvent bath. I did not have the confidence to do this without fear of introducing more damage. The vulnerable parts had also fortunately not been touched by apparent fluid entry and deposits.

When I repeated the process, I also carefully used a solvent-based circuit board cleaner spray in the final finish up and mopped that material off as well.

Unless a person has fine dextoral skills and is very, very careful, it is not an owner-operator task I would recommend. There are a few pieces inside which can be permanently injured.

If you are taking feeds from a mix deck, you might not observe the initiation noise described in the FAQs on the SD website.

I have had the Mix-Pre for about 5 years also. It has had one or two hard knocks but is still good.

Thus far I have only tested with internal batteries. The battery endurance using three channels of phantom power into three mikes until the mixer reports low power with the flashing light seems a little shorter than the Mix-Pre but it could also have been set up more conservatively.

The Mix-Pre power LED also changes from green to orange as the battery power drops. One does not always notice immediately. I have only been caught out once and that was when the mixer was on internal power and unattended for too long.

Until I have had the 302 checked by proper techs, I won't operate it with external power. I suspect that the LED chain might have been fed a direct overvoltage from the EXT-OFF-INT power switch, which is fixed into the same PCB that feeds the LED sub-board. That area had a heavy fine coverage of grey crystalline deposit among the switch pins.

Last edited by Bob Hart; July 14th, 2014 at 03:09 AM. Reason: error
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Old July 14th, 2014, 09:26 AM   #6
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Re: Sound devices sd-302 mixer

As I recall the 302's ext. power input is fused, (auto reset) so an over-voltage condition in unlikely.
I surmise you have some electonics experience Bob, I glad it's a usable condition. Shipping it to the motherhship (New Mexico, USA) would be expensive

FWIW and something to keep in mind, If you're using (a G2/3) unbalanced input device, if the Phantom Pwr. is engaged, it will drain the AA batteries fairy rapidly (about 5 min.). Been there done that. I would assume reduced run time on an ext. battery as well. This may apply to the MixPre as well.
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Old July 14th, 2014, 10:41 AM   #7
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Re: Sound devices sd-302 mixer

Hi Bob,

Sounds like you've pretty well gotten things sorted out. About the only problem I've had with SD gear was blowing the firewire interface in the 702, but SD is sort of "next door" to Arizona so not a big trip. Was a big $$$$ thing though - I seem to recall it was a few hundred $$$. I don't use FW anymore.

Anyhow, glad things seem to have settled down

Oh yeah - battery life. I've never had a problem with it running down the AA cells over a 2 to 3 hour period - maybe it would get down to half or something like that when running phantom power to the mics..
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Old July 14th, 2014, 11:51 AM   #8
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Re: Sound devices sd-302 mixer

The batteries probably had about three or even more hours up. I had three mikes, two Rode NT2a and one Sony directional, all of which seem to work best on 48v phantom so it is probably a fairly heavy test.

Also if the capacitor was self-discharging via a conductive path in the contamination, the power draw from the batteries likely increased in the effort to keep up. The initial crackle problem before I went inside was quite loud and consistent with that sort of leakage.

All seems good now. The mikes power up pretty noiselessly from go from an overnight rest, so the capacitor is probably holding charge longer unless there is a leakdown discharge circuit in there somewhere.

Firewire, for all its initial promises seemed to become a troublesome tech. A lot of JVC GY-HD*** family cameras burned firewire ports.
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Old July 14th, 2014, 11:35 PM   #9
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Re: Sound devices sd-302 mixer

Knock on wood - my JVC HD110 is still fully functional - no F/W issues. And lately I'm feeding component out to a couple of BM mini-converters (Component -> SDI, SDI->HDMI) and into an Atomos Ninja so I'm avoiding the whole F/W mess. I have to admit to severe trepidation every time I hooked up the F/W cable. Particularly because it wasn't practical to shut down my PC - I did however have an isolation box in the F/W chain. Even so I hated hooking it up. It was worth the $ just for the peace of mind!!! And it's getting harder to find a system with F/W anymore - good riddance!

A bit off topic I guess, but I really like the JVC and would hate to give it up. 720p is still just fine for YouTube!
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Old July 16th, 2014, 02:15 AM   #10
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Re: Sound devices sd-302 mixer

Famous last words. The issue is back.

A pattern seems to be, overnight cold, failure to initiate after power-on, LED chain lit up and very bright. The behaviour seems to be like in the days of old HF radio transceivers, a parasitic oscillation steals power, locking everything else down, then resolves itself as the thing warms up.

Have to save up a few dollars and cents and send it for a US holiday I think.

Thanks all for your good counsel and suggestions.
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Old July 16th, 2014, 12:07 PM   #11
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Re: Sound devices sd-302 mixer

Too bad

Sorry for all the trouble you're having. Hope it gets resolved.
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Old July 16th, 2014, 12:17 PM   #12
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Re: Sound devices sd-302 mixer

Sorry Bob, It appears you'll have to bite the bullet and send it for repair.
I assumed you asked SD if there's any repair facilities in Australia.
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Old July 18th, 2014, 08:45 AM   #13
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Re: Sound devices sd-302 mixer

Rick.

SD's resellers in Australia are over east, which is about a quarter of a world away from this side of Australia. I bought this one used from offshore.

By the time one packs something up and pays to send over East, it is not much furthur or expensive for it to go all the way home to the best expert, the manufacturer.

Just for kicks, I have chucked a couple of dessicator cylinders from of vitamin bottles in it to see if this makes a difference over time. If it does, it means there is a patch of hydroscopic deposit in a tiny place somewhere I could not get at. Four days now, and initialisation problem has not reared up again. Curiouser and curioser but yes it will need to travel.

It will have to wait a few months as the cash is being swallowed up by an editing computer rebuild. That died a while back and I have endured two years of spraying it with freezing spray and jiggling motherboard joints to keep it struggling along.
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Old July 19th, 2014, 07:48 AM   #14
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Re: Sound devices sd-302 mixer

Footnote:

I forgot to mention, the available space inside the entrails of the SD-302 is extremely limited. The designers did a masterful job of form and function and economy of space.

To make the dessicant cylinders from vitamin bottles fit within a small space adjacent the third audio channel transformer, the cylinders need to be cut down to about 8mm depth, which means about half the dessicant crystals in each have to be removed. This raises an opportunity to dehydrate the crystals before installing them in the shortened cylinders.

Firstly a thin cardboard disk has to be prised out of the cylinder in which it is engaged in a shallow groove.

Once the cylinder is cut down, then there no longer remains a groove. The cardboard disk has to be crushed into the space on top of the crystals and retained by melting folds in the plastic walls over the edges of the disk for positive retention of the disk.

If I do this again, for a tidier job, I think I will trim the bases off, cut down the tube walls then fuse the shortened cylinders back onto the bases with the soldering iron method.

Last edited by Bob Hart; July 19th, 2014 at 07:50 AM. Reason: error
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Old July 19th, 2014, 01:00 PM   #15
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Re: Sound devices sd-302 mixer

I've always wondered why they didn't make the unit a tad wider so the battery compartment didn't project out past the side of the device - seems kind of strange to me. Oh well, doesn't much matter since I don't use it very often anymore - I do almost everything now with a single stereo (M/S) pair directly into the 702.
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