C-audio SR606 Power Amplifier

[kamskoma]

Hi,

I need information regarding mods and schematics for a C-Audio SR606 this is an English company I don't know the factory name but C-Audio and/or Cambridge Electronics is printed on the amplifiers it is NOT the Cambridge Audio HiFi company.

The problem is in the primary of power supply the soft start circuit has a problem, Poff and Blue smoke has occured!

Kamskoma

[anatech]

Hi Kamskoma,
Check the simple stuff first. Look at the rectifiers, main filter caps and output transistors. Anything that goes short there will take out the soft start as well.

Soft start circuits are great at limiting the amount of damage that can occur in an amplifier!

-Chris

[kamskoma]

The problem is that the large 47 Ohm resistor in series with 230V primary has blown, I think this resistor should be 10 Ohm as I have seen in other BIG amplifiers , this is a BIG amplifier with a Big toroidal transformer.

A rely will short the resistor after a while maybe the time delay circuit is broken.

Need info maybe some English member can help.

Kamskoma

[anatech]

Hi Kamskoma,
Okay, the soft start resistor can be shorted out temporarily. You will need to troubleshoot further as the unit has drawn excessive current causing the soft start to burn open.

Connect the unit to a variac after shorting the resistor, never plug it directly in until the resistor has been replaced with the same value. If you don't have a variac, you must use a low wattage lamp in series.

If you test the rectifiers and output transistors I will bet you'll find a short somewhere. I have seen the odd filter cap short without venting. You must find these faults before attempting to repair thesoft start circuit.

If you replace the resistor now, short it out and follow my advice before applying full power. If you do otherwise you will extend the amount of damage there already is.

-Chris

[pinkmouse]

The SR606s are very reliable amps, so much so that I have never had to open one up apart from when I had to swap out a broken speaker post.

However, if I remember correctly they use a rectifier bridge with push on spade terminals. Disconnect those, wrap a bit of tape around them to prevent them shorting to anything, then you can test the soft start circuit without risking anything.

[anatech]

Hi Al,
Do you have a schematic?

In my service experience, I've never had the surge resistor go unless one of two things happened. Amplifier fault or technician slow starting without shorting the part. There is always a first time though.

-Chris

[pinkmouse]

Originally posted by anatech
Hi Al,
Do you have a schematic?

I haven't, but I know someone that has! It may take a while to get it though as I'll need to visit and probably end up having a liquid lunch.

Kamskoma, I've changed the name of the thread to something a little more informative.

[anatech]

That doesn't sound like a bad thing

I'd be happy to join you, but there is a bit of water between us (and a few time zones).

-Chris

[kamskoma]

Thanks a lot for your kindness.

Ok, I found the schematics(old) but it shows that the soft start resistor should be 10 Ohm/50W not 47 Ohm/50W as I found in my two SR606.

For many years ago I troubleshoot a SR606 and I will remember that C-Audio had some problem with the rely circuit.

A Schrack 48V DC relay is the relay that shorts the 47 Ohm resistor ( there is three relays in this amplifier).

My idea is; if the resistor has 230V for a too long period it will blow, and the timing circuit may have some problem or if the shorting relay dont short the resistor effectively.

I can run one of the amps and it works OK but the resistor in this working amp looks very funny the internal resistor body have moved a bit from its housing ( it preparing it self for a small explosion and blue smoke).

I think that Mr CA have done some modification to this circuit but what and where can I get this information.

One more problem Tyco/Schrack has no 48V DC relay in their product catalogue, the relay types is RM805615 (115V AC) and RM 805048 (48V DC).

I have two more SR606 in alles four with exactly the same problem?????

So..... if I could fix them it would be nice.

I'll try to scan the schematics and send them in next reply.

Thank you

Kamskoma


Kamskoma

[707dave]

The soft start circuit blowing up can sometimes be an o/p device failing. The energy in the Psu is enough to cause a shorted o/p device to go open circuit so when you repair the soft start the origional fault is no longer evident.