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Hi from Magic Sam


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I am a semi-retired electronic technician who is also a performing musician and sound engineer. I have been repairing electronics all my life and have worked on a few of Bob Carvers amplifiers. I was hoping someone had a service manual for a Sunfire True Subwoofer. A tech friend used to service these but is no longer working in audio.

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Hello magicsam and welcome!

 

There are Truesub schematics, and we have a fair working knowledge of the typical problems that are encountered. There are several different circuits for the various models, so you need to tell us what model you need help with, and give some idea of what the symptoms are.

 

RobertR

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Welcome.jpg.4aca7dd3d96455c938bfb9181f9e40cb.jpg

 

Welcome to the site, @magicsam!  I won't offer help on the technical side - I'm the antithesis of RobertR when it comes to electronics, and I would gladly defer anything remotely in that realm to him.

 

Do put together a post with the info Robert suggested and asking things a bit more directly, and I would expect that the wizards of electronics, here, will come along with all you may want to know, in a bit.


For now, make sure you take time to enjoy the music - live or recorded, or in your case, perhaps going from one to the other.

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     Thanks guys! I believe this is an oldie, the serial number is 9611302256, which the last four digits are inside the panel as 2256 in marker pen. My friend said they are prone to capacitor failure, both the two main filters and several power supply caps. I have ordered some new from Mouser. I did already replace three IRF630 FETS and their gate resistors (9.1 ohm/ 1/6w) and also did find a cold solder joint on the back of the AC fuse holder.

     The speaker now does function somewhat, but with a background hum and occasional  popping noises. Any hints you can give would be appreciated. :)

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S/N says 1996 - probably an Original TS model – someone correct me if I'm wrong – never had one that old. Whatever the age, capacitor failure is certainly most likely, as your friend says, in fact it's a near-certainty, but I'd suspect the smaller electrolytics before the two biggest ones. Most of those smaller and mid-sized caps run all the time the unit is plugged in, filtering the low voltage DC supplies, and at this point ought to have been replaced long since. Use 105o types whenever you can get them – they really last longer.

 

BTW, with those big caps, at least one of them stays charged quite a while after unplugging the unit, and it's got enough voltage (AC line voltage x 1.414) to make you wish you hadn't discharged it though your hand or whatever, if you get careless.

 

If you're looking for the power transformer, check outside – it's that big thing that belongs to the electric company. The line voltage goes right to the rectifier diodes.

 

Personally, I keep mine unplugged when not in use. As stated above, those low voltage supply filters never rest when she's plugged in, even though the output stage shuts off automatically.

 

Another known problem, at least in later versions, is faulty/dirty controls, sometimes curable by the right spray cleaner and some repeated turning, end-to-end.  Post a few pics if you can figure out how; if not, somebody will help you.

 

RR

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Welcome @magicsam.  

 

Always check the manuals library, for any manuals we have here.  See the top menu bar, fourth item from the left "Manuals Database"... it's a bit clunky, but it holds the brain-trust of what people here have shared in their manuals collection over the years.

 

If you happen to find any docs not there - please share them here in PDF, so we can keep the momentum going.

 

Another good suggestion is to do a search on a keyword.  There are several threads from members that have fixed Sunfire Subs, that may help you.

 

...and, if you want to start a thread on your own fix, that would add to that brain-trust too.

 

pictures, ... lots of pictures ! 😉 

Edited by AndrewJohn
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     You are all very friendly, thanks!

     RobertR, I have been fixing electronics a long time, a 60 watt light bulb with alligator clips has been my cap discharge tool for years.

     And yes, I think this one is an original TS. I have a bunch of the 470uF/25V  due any day, along with two 2700uF/200V and two 47uF/200V that are in the power supply. Sort of the shotgun repair technique! Those first caps are under a lot of stress, especially since they are run half wave, lots of ripple current!  I have also considered adding an inrush current limiter to protect the bridge rectifier and the caps.

     I will keep you all updated as I go, thanks for your support.

    

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The Mark II model came out in the mid-90s.  If yours is a Mark II it should say so; otherwise probably the earlier model, with larger drivers.  I don't have the older schematic, but I suspect it's very similar, and assuming it is, you are going to need more caps than you mentioned.  Just 4.7 mf size alone probably number over a dozen, and after two and a half decades they are all ripe for replacement.  Many involved in 12 and 13 volt DC supplies.

Didn't mean to insult your intelligence about discharging caps, but figure better chancing that than somebody gets floored...

RobertR

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     Hi again RobertR!  No, I was not insulted, better safe than sorry.

     If you could send me the schematic you do have it would be a great help to understand the topology of these designs. I have been a factory trained Crown Audio technician, in fact one of the instructors at Crown school was in my high school electronics classes. I sat in the back and resisted the urges to heckle him!

     My parts order was on my doorstep this last weekend, repair is soon. My patient is definitely older than MkII and a roadmap is something I could appreciate. I am fairly good at reverse engineering, the MkII roadmap would easily help understand where the highest stress components are.

     Thanks again for your input and I hope to hear from you soon!

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magicsam,

The Mk2 schematic I have was just submitted to the Forum; it's in the form of digital photos of Sunfire's drafts, and after some needed technical upgrading  hopefully it will soon appear in the Sunfire Schematic section, along with a few others I had.  The two boards are 653-010 Rev. B-1, and 653-011 Rev. C-3, meaning (as best I can guess) that they are the tenth and eleventh board designs that Sunfire ever produced; they're dated Jan. 1995.  Hopefully the same as in the originals.  Look on your boards for such numbers as those. 

The original 2-channel amp, Sunfire's first product, contains boards 653-001, 002, 003, 004, & 005, so you get the idea - 010 & 011 are early.

 

In the True Subs I've fixed, all the electrolytics are usually pretty tired.  If you have a cap tester, remove and try a few of the smaller ones.  If they are labeled 4.7 at whatever voltage, the capacitance should test at least that high.  Among these smaller electrolytics, new ones most always seem to test comfortably over spec.  but old well-used ones start to sink below rated value before they crap out completely.

 

One of the symptoms that shows up first is failure to stay on - automatic shutoff takes it  back to standby mode right after the bass drum hit that got it to turn on at all.  That shutdown circuit cutoff depends not only on the electrolytic that discharges over 10 minutes of no bass signal, but  also on other caps that filter the regulated the DC supply that charges it in the first place.

 

I'd strongly advise against trying to out engineer Bob Carver.  That circuit is complicated, with lots of safety goodies.  Best to leave it as Bob intended.

For longevity, again I recommend unplugging it when not using it for any extended period.

 

RR

 

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  • 1 month later...

Wow, the Sunfire sure is a beast! I replaced 13 of the 470uF filters on both boards and two 47uF 200V in the regulating section.  It works well but has a slight hum that increases slightly with more gain. I still want to know if any more tips on getting this cured?

 

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