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I have gone ahead and made the change on C40 - added 3.3K in series to C40, which I changed to 100uF.. I now have a good startup delay, of around 7secs.. happy with that. the shut down delay and balance spike, seems to be caused by the filter caps discharging at different rates. not sure which...

I am going with putting a series resistor to C40, to slow down turn on, and it wont affect protection calcs.. thats a good compromise for turn on.. ill live with turn off for a while.. its not too bad in terms of speaker thump. thank you for your input Steve, its been invaluable.

Oh thats right, we usually have a diode across the relay coil for back emf. but why is it connected to the -ve rail, instead of 0V

"'ve seen a similar setup in a sub amp. The cap is solely to prevent start up conditions from triggering the protection circuit, as once it's triggered, power has to be removed before it will start. So discharging it quicker won't turn the relay off." thanks for the feedback. very informative...

what if I put a pull down across C40, to allow it to discharge quicker?

not even with the text :) now you know how feel

I have a P50, that seems to have a slow protection off timing, meaning when I turn off the amp, there is about 3 sec delay before the speaker relay turns off. to me, it should be instantaneous off, when I turn off the amp. I have tried to decode the schematic, and work out what needs to be...

Attached. I think I’ll do the other side, so I don’t have to delve back in there again. ‘thank you to all that have contributed..very much appreciated

If anyone is interested, this is now sorted. Just to recap, when you know what the problem is, and you know where the issue should be, measuring this problem out dynamically is not feasible, due to the feedback path making things complex. So you go about measuring thing’s statically. so when...

Ha, r21 was my first port of call, when I first checked this..it’s good. Swapped tr4 and 5, and no change. D3 is good as well. I have also reflowed the whole board..in desperation

Yes, that is correct.. tr3 has +ve voltage on the base and emitter (As per schematic), but -ve on the collector.. That’s the puzzling thing.. we know what’s wrong, we know what causes this behaviour, but no component (on its own) is misbehaving. not sure what else could cause this.

Tr1 and 2 have been swapped with the good channel.. they measured ok, but I swapped them just in case. They are good.

Yes, all measure ok.

Yes, tr3 has been swapped out.. no change. The base of tr3 (which is connected to the 33k), is reading correct voltage, as per schematic.

Just a bit of background, I’ve had this for about 20years, but it’s been in the shelf, as it had some transit damage when I got it, and kinda left it there, until recently. Cant remember whether it worked or not, but here goes now. One channel has rail voltage on the output so it won’t come out...

Yeah, mine a 3 way, and the speaker connectors are towards the bottom of the cab. They have very good range..and tight bass.

I have had these for about 20yrs, but never bothered to work out what model they are. I don’t suppose someone out there has seen these and knows the model number? I’d say they used to have stickers on the back, but they are long gone.

Noboby wants a crack at this??

I have this sub, that has blown output fets and fuse.. I have replaced both fets, and to be on the safe side, I also replaced both opamps and Q610 I hooked up an amp meter on the fuse holder, and slowly brought up the voltage on a variac. no sooner there is about +-6v dc on the rails, the...

This is not believable. It looks like all the record wires are disconnected. Question is, what the hell is connected to the heads that are on there? Are these really 280ss heads or just 280d heads someone has put in?/ Because the heads only have 4 pins, whilst in the manual, the photo has 8...

hi all, as the title suggests, it won’t actually record (in record mode), but is erasing, to summarise what I have diagnosed: Oscillator working, with a 70v p2p output on the scope Although not sure what frequency it should be. I measured around 220khz.(not sure what it should be) The input...

thing is, if its working (as in producing good sound), I guess the sparking can be easily fixed by a tech.. I mean, it is working as well, right?

I am now super confused. if two stations, on the same frequency, and one is more powerful, wont you always pick up the more powerful one? how is a tuner supposed to know, especially if they are on the same frequency. now if they are not on the same frequency, then I understand your response..

yes the main board at the bottom. from memory there should be 8..D409-412, and D417-420. if some are barely lit, that can still be a bad solder joint. I once had to go over the whole main board, every point, to make it work.. it needed nothing else but that. by all means, check the main output...

from experience, these are notorious for having bad solder joints on the main board, which will cause DC to be present as well. if not all the LEDs are lit on the main board (make sure you have identified all of them, as sometimes you will miss one), the servo will not work properly, and voila...