CR-620 sometimes coming out of protection to early causing speaker thump

Eastham

More Class-A than ever!
So my 620 has now started coming out of protection to early causing a negative spike at the speaker terminals, it happens from a cold start after it's been off for a while or if I turn the receiver off then back on after a second.
When it comes out of protection normally it takes around 3.5s for the relay to close when it opens to early it takes around a second to 1.5s to close.

Voltages at TR809 are as follows:
Base: 21v while relay is open, 12.5v after the relay closes
Collector: 0v while relay is open, 13.22 after the relay closes
Emitter: 21.5v while relay is open, 13.28v after the relay closes

Any ideas what I should check?
 
Reflow the solder connections for TR808 and 809. If that doesn't help replace them.
 
it takes around 3.5s for the relay to close when it opens to early it takes around a second to 1.5s to close.
Let me try to get this right. You turn on the unit. It normally takes 3.5s for the relay to click? When it acts up it clicks at about 1.5s.? There should be no delay at power down , It should instantly open the contacts at power off.
 
Let me try to get this right. You turn on the unit. It normally takes 3.5s for the relay to click? When it acts up it clicks at about 1.5s.? There should be no delay at power down , It should instantly open the contacts at power off.

Yep and instant off.
 
I replaced TR808 with a KSC1845 and the flyback diode for the relay with a 1N4001 to no avail. I've ordered a KSP2907ATA to replace TR809 which is a 2SB544. I also went around the power supply, amp and protection circuits touching up all the solder joints again for good measure.
 
Let me try to get this right. You turn on the unit. It normally takes 3.5s for the relay to click? When it acts up it clicks at about 1.5s.? There should be no delay at power down , It should instantly open the contacts at power off.
Have a close look at C815 and 816 as well. Especially C816 small violet colored 33µf/16v. These are quite often -- bad --.
 
Have a close look at C815 and 816 as well. Especially C816 small violet colored 33µf/16v. These are quite often -- bad --.

I gave this receiver a full re-cap about 2ish years ago, I used Panasonic FC type capacitors.

I have never in 40 yrs found a bad relay flyback diode.

I think I'll probably end up re installing the original flyback diode, it's probably better suited for the job.

Things that may be worth noting, I did change the original filter caps out for higher value 10,000µF Vishay caps, I've also replaced the protection relay with a Omron MY2N 12DC(S) as the contacts on the original relay where fubar despite this unit looking like it'd never been used but the problem was there beforehand, I was hoping replacing they relay would stop the thump.
 
Good to know..Well lets hope the relay driver TR809 does the trick.
 
Good to know..Well lets hope the relay driver TR809 does the trick.

I think I may have found the issue... I think If my guessing is correct, I've replaced C815 with a 47µF instead of a 4.7... Is C815 located directly below TR807 by any chance?
 
I'm such a tool, looks like it was the problem after all... I'm gonna let the receiver sit for a half hour and see if it thumps when I turn it on but so far everything seems gravy... I think I need to get my eyes checked... Thanks Avionic!
 
Little cap closest to TR807 is 4.7µf/35v verified on a parts unit I have here.
 
Little cap closest to TR807 is 4.7µf/35v verified on a parts unit I have here.

Yep, I put the wrong cap in when I re-capped it. Wonder why I never noticed the thump before, everything seems fine now. Relay always takes over 3 seconds to click and no more thump.
 
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