SA-9100 Protection releasing too soon.

[QSilver]

I've been going through a very abused SA-9100. To cut a long story short, I looked through a number of threads dealing with them and rebuilt the power supply and all the other boards, powered on and everything is great except for this one problem.

I read that the protection shouldn't disengage (and connect the speakers) until around 5 seconds after power on.

Mine disengages reliably at 2.5 seconds. If this is the first power on for a while, I get a little pop through the speakers. So the amp isn't quite ready. I checked which section was causing the pop and when I separate pre and power amp, the pop doesn't happen.

But seeing as everything is working and the pop happens at 2.5 seconds, I think I must've got something wrong in the protection circuit. I replaced all transistors and capacitors and only have to add the fly back diode but I want to try and fix this first. If I use the speaker switch at start up, count to 5 and then switch the speakers on myself there is no pop.

I replaced the transistors like this:

Q1,2,3 and 4 were changed to KSC1845FTA
Q5 changed to KSA992FBU
Q6 changed to KSC2383
Q7 changed to KSC2690

Maybe some of the transistors I've used are over sensitive in triggering?

 

[petehall347]

what capacitors did you use ?
if its still a 100uf in c6 then try a 220uf in its place ..that should slow things down a little .

 

[QSilver]

All capacitors I took out I replaced with what the schematic said. Whoever was there before me had put in some 320uF capacitors in C3 and C4. I changed these out for 330uF 35V (didn't have any 6V). The rest I swapped like for like which matched the schematic.

C6 is still 100uF, I'll try swapping it for 220uF - thanks.

 

[QSilver]

Yes, that worked. Clicks over after about 5 seconds now and no pop through the speakers. But how come the circuit is seemingly quicker now?

 

[petehall347]

circuit is actually slower not quicker ... ..220 uf charges slower than 100uf ..
i should have said to be sure r27 is correct at 22 ohms ....?
all should be fine now anyway.... best check it though to be sure .

 

[QSilver]

R27 measures correct at 22R.

circuit is actually slower not quicker ... ..220 uf charges slower than 100uf ..

Sorry, yes, I meant quicker when the 100uF cap was in. I imagine from new with those capacitors in it would come out of protection after 5 seconds. I was wondering what I might've done to make it quicker to come out.

 

[petehall347]

i cant figure that bit out ..
maybe someone else will have an explanation ....