SPL-1000 amp. released magic smoke...

[fezder]

Hi, i again posti my question, so here's the deal: my SPL-1000 (2x500w @ 4 ohm) amplifier popped when i was using it. I investigated situtation, and it seems amplifier transistors went S/C as dmm gives S/C reading on continuity check, between ALL pins, base, emitter collector, on both npn and pnp transistors. also, they popped 220r resistors too with them. everything else seems to be intact, no blown caps etc....i checked parts between two channels, they werre indetical, i used only one channel.and i have replacement parts available. And, if someone wonder,s why i dont send it to warranty/repair, the reason is simple: warranty expired 2 monts ago (sigh), and theyr prices make repair cost more than new amp. So, i ask you now, how can i improwe this models durability, as i drived it about half volume, so it shouldnt pop. any suggestions? i am going go get/buy dc protection circuit for speakers, but how can transistors durability be increased? i hope you understand this case

 

[cowboybob]

Can you give us a schematic of the amp? Or at least some HD pix?

I googled "SPL-1000 amp" and got nothing useful.

 

[fezder]

yeah, sure, i just forgot to add them beforehand, ill post them soon, none schematics were found, but pictures are no problem, i'll post them soon.

 

[fezder]

ok, here are the photos i took, i hope they are useful at some matter that is
the components that are destroyed are: TIP41/42, 220R resistors, everything else seems intact, with dmm too
https://i50.tinypic.com/acaddx.jpg
https://i49.tinypic.com/2ed1qbo.jpg

*edit: i took transistors off already, to make sure they are destroyed, and connections are also, left out from disassembly process.

 

[Nigel Goodwin]

Are there some larger transistors mounted elsewhere? - TIP41/42 are only medium power devices, perhaps managing 35/50W at a push - certainly no where near 100W, never mind 500W. They are commonly used at drivers, not as outputs.

What voltages do you have on the supply rails?.

 

[fezder]

yeahm i thought same when looking at their datasheets, no way they can deliver 500w i checked amplifier over and around, but there were no other amplifiers, only those tip's....do you mean by the supply rail the voltage from transformer, or the output for speakers?
hmm, could it be that main stage is missing?....

edit: here's the manual, which confirms 2x500w @4 ohm
https://www.electro-tech-online.com/custompdfs/2012/11/178_794.pdf

 

[alec_t]

I suspect those '500 Watts' are the special "advertiser's music watts". If you divide by 10 or so you might be nearer the real RMS Watts that the amp can provide.

 

[fezder]

haha, makes sense, it was so cheap, about 100$ price range, so im not surprised, i read once about these ''fake watts'', but i thought its just talk.....well now i'm this bit wiser to thing about it, i think 1kw is little too much of power for home use after all....

 

[Nigel Goodwin]

yeahm i thought same when looking at their datasheets, no way they can deliver 500w i checked amplifier over and around, but there were no other amplifiers, only those tip's....do you mean by the supply rail the voltage from transformer

The DC voltage rails, across those two big black capacitors.

For a 100W amplifier you should have about 35V DC across each of them, for 250W about 50V each, and for 500W about 70/75V.

 

[fezder]

ah now i got it, ill test them tomorrow, and post results then

 

[unclejed613]

from the pics you posted, the damage extends further back than just the outputs.... i've seen amps fried all the way back to the input stage. there are probably several resistors burned open there, as well as some diodes.. if you must remove transistors to test them, do it one at a time, replacing the bad ones as you go, and returning the good ones to the circuit, that way you won't forget which one goes where.

 

[fezder]

hmm, newer thought damage would go that far, thanks for info

 

[fezder]

ok, i made some progress with repairs. Here's what i found out: in addition to my previous discoveries, i found two 0.47ohm/2w , and two 10ohm_1/4w resistors burnt, the was as unclejed provided info, (thanks uncle for info regarding open burnt resitors, newer knew about that ).....and one interesting thing i discovered, was that ac voltages safe-grounding (if thats the right term), is soldered to speakers output negative terminal, this is too something new to me . But, i found those components destroyed, so is it wise to get the spare parts, as it seems this is repairable? or what you think?

 

[Nigel Goodwin]

ok, i made some progress with repairs. Here's what i found out: in addition to my previous discoveries, i found two 0.47ohm/2w , and two 10ohm_1/4w resistors burnt, the was as unclejed provided info, (thanks uncle for info regarding open burnt resitors, newer knew about that ).....and one interesting thing i discovered, was that ac voltages safe-grounding (if thats the right term), is soldered to speakers output negative terminal, this is too something new to me . But, i found those components destroyed, so is it wise to get the spare parts, as it seems this is repairable? or what you think?

Have you measured the voltage rails yet?.

It should be repairable - but as mentioned, it's likely that various other components have failed, it's common for an attempted repair to fail because not all faulty items were changed, one of which was probably the actual cause of the failure.

 

[fezder]

i didn't measure those yet, but i'll measure them soon. just to make sure, do i need to put any of those broken components back, or can this measurement done without them to be actually on PCB? and, whats importance of measuring voltage rails? to make sure transformer/caps are intact, or is there some other reason?

 

[Nigel Goodwin]

i didn't measure those yet, but i'll measure them soon. just to make sure, do i need to put any of those broken components back, or can this measurement done without them to be actually on PCB? and, whats importance of measuring voltage rails? to make sure transformer/caps are intact, or is there some other reason?

Just to check what the actual power of the amplifier is likely to be - it's a function of the supply rail voltages, and the speaker impedance - and that's basically all. The amplifier doesn't rally contribute to the output power specs, apart from if it's not powerful enough to match the supply rails it will be destroyed.

It should be fine to check without the components in place, they are the emitter resistors for the outputs (0.47), and the 10 ohms probably for the drivers.

 

[unclejed613]

judging by the large electrolytics to the right, your rail voltages should be 20 to 22V. the 2N5551 transistors in the foreground are the diff amps, but since there's a pair of 2N5401's opposite them i suspect this amp may have symmetrical diff amps. the taller transistors near the outputs are the drivers, and are likely shorted or open. the next two transistors are voltage amplifiers (going from left to right) and next are the current sources for the diff amps (again just guessing from the layout that this is using symmetrical diff amps, one for the + side, and one for the - side). it's also entirely possible that i guessed wrong about the two caps, and that the caps, the zener diodes and large resistors near them are a +/-15V regulator circuit going to the preamp stage, and your rail voltages may be somewhere between 30-40V.

what is the voltage rating of the very large caps in the first picture?

 

[fezder]

the big one electrolytics are rated 50v/4700uf, and i measured voltages over them, it was about 46v on both of them

 

[unclejed613]

so we're only talking about 40-50 watts, not 500 "whatts" (tnx AG, i really like that term for imaginary marketing wattage)..... i wouldn't recommend running this amp into 4 ohm loads either, as you reach the edge of the transistor's safe operating areas rather quickly. in the mean time, check all of the transistors, any resistors associated with bad transistors and all of the diodes. it looks as if there's no thermal compensation for the output transistor bias, so i imagine some of those diodes are part of a fixed bias scheme.

 

[fezder]

ok, so what is the formula for correct wattage? and is there any way to add thermal compensation, or this too complex? i read somewhere about adding silicon diodes from transistors base to ground, but i dont want to fry anything from uncorrect tweaking and, you said not 4ohm loads, welll i used 4ohm speakers, not surprise then it burned....