Dayton SPA250 Plate Amplifier repair help

No, with the modifications, the amp made a terrible "pop" at power one, then a strange "fire crackle" sound that slowly got louder and lower over 5 seconds before I pulled the plug.

I don't think these noises are related to the soft-limit circuit. TMM also disabled that circuit and didn't report any noise issues. After noticing similar noises I also tried moving the pots and switches through their ranges but got no changes in the noise problem. It was only when I disassembled the auto-on-off switch and cleaned it up that the noises stopped. Might be worth a try.
 
Ok, slight update on my amp. In my amp R22 is 120K and R23 is 2.3K. I lowered the gain of the power amp to around 20 by placing an additional 68K resistor and 22pF cap in parallel with R23.

The amp didn't seem to be oscillating however I can't be 100% sure of this because i only had my scope connected across the load (after the choke installed on the speaker wires), and a current probe on the mains input. It wasn't drawing any more current from mains compared to stock though.

I tested it up to clipping with an 8ohm dummy load (=~170W) which went fine and had lowered it to around 15Vrms output when it popped the mains fuse (3A fast blow - my mains is ~245V). I put another fuse in and it instantly popped it again.

After some investigation, one of the output transistor pairs is blown (everything shorted together) but the other pair is ok. Emitter resistors measure ok. The output transistors are knockoff 2SA1962 and 2SC5242 (marked 'K A1962A' and 'K C5242A'). Q15 is also bad (2SC2800), maybe more. I'm putting it down to dodgy knockoff transistors at this stage, going to order reputable replacements, pop them in and see what happens unless someone can convince me otherwise :).
 
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low side driver is blown too (2SA1700). I'm a newbie to amplifier design but 2SC2800 and 2SC1700 seem like really strange choices for drivers?

Will have to desolder them to check the transistors before them, it's late here so that's a job for another day.
 
5Watt will be enough.

I managed fix my blown output stage briefly before it blew again. Can't be bothered fixing it again because tracks are already starting to lift on the crappy quality PCB, so i'm designing my own drop-in replacement power amplifier. http://tinyurl.com/prwea55

The original power amplifier design is really average anyway. To call it stable for 4ohm loads is really borderline and there is very little to protect the speaker or the amp when something goes wrong.
 
5Watt will be enough.

I managed fix my blown output stage briefly before it blew again. Can't be bothered fixing it again because tracks are already starting to lift on the crappy quality PCB, so i'm designing my own drop-in replacement power amplifier. http://tinyurl.com/prwea55

The original power amplifier design is really average anyway. To call it stable for 4ohm loads is really borderline and there is very little to protect the speaker or the amp when something goes wrong.
Nice, mine is behaving better now after 5W resistor replacements, but still warms up and when hot it emits 'scratchy sounds' still, but no large pops anymore. Please let me know how your amp design goes, TMM, when will you build?
 
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OK here's the deal. The amp can be operated without the soft limit (SL) circuit thus eliminating the burnt resistor problem altogether. Without the SL circuit the amp can be over driven which will result in distortion. That's really the only downside. If you're careful to set the gain at a reasonable level you shouldn't have a problem. To disable the SL remove the burnt resistors from the board. Then remove the photoresistor assembly labeled U2. You then replace the resistor part of U2 with a 10k fixed resistor (see attached pic). Button it up and you're ready to go.

With these changes on my amp a 1v RMS input at 100Hz will produce an undistorted output of 65v p-p into 8 ohms with the gain control set midway and the freq control set at 180 Hz. That's right around 250 watts. If you are driving the amp from a receivers LF line output you should have no trouble getting to full power out.

Can't promise this will eliminate the pops you mentioned but mine plays clean.
I disabled the soft-limit circuit tonight and was a little confused by the recommendation to replace U2 with a 10k resistor when the picture showed what looked like a 200k to me. I used a 220k that i found in my box. It's working well at the moment, though as you might expect, the gain control must be turned up further to produce the same output range now. Should I go back in and try a 10k?! Hate to mess with it now that the bad sounds are all gone!
 
This one went really south

Not sure if I can repair it, but anyone know the values for r30-r33 on the main PCB?
 

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Burnt resistors on my SA240 were OK, however, heating ruined the solder joint. The PWB is not designed for repair and it is no fun to tear it apart. The pads lift very easily. When the soft limit circuit goes south the output level decreases. Thanks for all the great discussion, I'm repairing mine now.
 
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Spa250 repair

This PWB is so broken it's not possible to repair. When I removed the "L" shaped support attached to the upright auxiliary board (+/- 15 VDC) I damaged every one of the right angle solder joints which connect the smaller board to the PS main board, what a mess that is. Solution - checking Aliexpress I found a complete 150w subwoofer assembly which requires +/- 40Vac and a heatsink. "150watt sub amp"

Two piece construction, high level, low level inputs, auto on/off. You need a heatsink, transformer, a little bit of machining, hole drilling and the destroyed SPA240 or SPA250 could be repurposed for $Au 65.00 with free shipping. That's a bargain in my book.
 
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Hi,
I've been through three of the Dayton Audio SPA250 plate amplifiers over the last three years. This is my third one, and PartsExpress is no longer interested in honoring their warranty.
The failure is always the same; It starts popping. One pop here. One pop there. It can be 10 minutes between pops, or four days, and at any time of the day or night with no regard to source being active or not. Eventually, it just barely works.

I'm driving a single Dayton Audio RSS265HF-4 10" Reference HF Subwoofer 4 Ohm, sealed in a sealed enclosure, using the dedicated sub-woofer output of my Onkyo amplifier to feed the plate.

Q: If anyone has this amplifier, would you be willing to help me identify the two resistors shown in this picture? Specifically, could you open your amp and take some photos/color bands from it?

You'll notice everything is nicely charred. However, I could not find any other evidence of blown components.

Thanks greatly, in advance.

Got a new one today. Looks like those resistors are now 3.0K and 2W
See pic.
 

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I was getting low and sometimes no output from the SA250-B in my home made sub. Resistors RS1 and RS2 were burnt but still tested OK with a multi-meter. I suspected that they were failing intermittently when under load (current => heat).

After I cut them out (disabling the amps soft-clip circuit) the amp performed better than new. I even had to remove the grill from the front of the sub because the front mounted 10" Pyle PL1090BL now had enough excursion to hit it!

I definitely recommend this mod.
 
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Great thread -
Similar amp in my Ikon CM6800's Same S200ETH V1.1 but with S01BDRV V1.1,
Does anyone have leads on a schematic for the S01BDRV V1.1 instead of the S01ABDRV V1.1.
From my research looks like a re branded KLH E205870 used in these speakers.
Not having much luck in tracking it down yet.
 
Hi Guys,

My 6 year-old SA240 amp fried a month ago i tried to replace the transistors but with no success, the PCB is of low quality, so i replaced it with an Infinity TSS-1200 for $120 but it won't match with my Bose 301 fronts. My SA240 cost $98 + $100 shipping at that time (from PE to Philippines).

So i planned to reuse the Transformer, Heatsink and the Preamp of my old SA240 with this amp from Aliexpress (attached).

An externally hosted image should be here but it was not working when we last tested it.


A3-BASS 300W high-power subwoofer amplifier board can do single-channel full frequency
55VX2 300W
33VX2 140W
28VX2 90W
24VX2 70W
18VX2 40W

My question is can i just use the SIN, +18V and Ground of the preamp without using the other 3 jumpers (Standby, Protection and Temperature)?

An externally hosted image should be here but it was not working when we last tested it.


Thank you in advance!
 
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Ugh, Anybody Have an SA240-B or the schematic?

Has anyone successfully repaired an SA240? On the soft limit switch I have two burnt resistors. Are they the same value as on the SPA250?

And U2 with the heat shrink wrap looks a bit cooked.

I'm thinking of using the SPA250 schematic as a rough guide.

I'm guessing I probably have some components before and definitely after those resistors that took some unwarranted current and/or heat (zenor diodes, etc, etc).

Oddly, all my capacitors appear brand new.

More useless complaints below.

I then have one bleeder resistor near the large capacitor that got toasty.

My frequency pot is also stiff when turning. And both gain and frequency pots have overextended their printed ranges.

I freaking hate this POS amp but am determined to fix it for less than $5. ;)