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Old 21st January 2012, 01:49 PM   #1
Wendyb is offline Wendyb  United Kingdom
diyAudio Member
Join Date: Jan 2012
Location: Norfolk, England

I've been looking at mending my partners Mission 778 with my Dad and I can't get hold of a circuit diagram anywhere. Mission said the circuit diagrams had all caught fire 13 years ago!! When I phoned them again they said Cyrus probably had the circuit, so I phoned Cyrus and they didn't have it.

Anyway, we have replaced 2 x 100uf 63v capacitors and put the other 2 old ones back in,(the insulation had melted on one cap and another had snapped easily on inpection). This didn't sort it out, but still waiting for 2 other new ones from Maplins.

Then we replaced 2 x LM317T 1.5A Adjustable Voltage Regulators as there were cracks in one, it also had to be attached to a heat sync. But it still doesn't work. Dad thinks it may be the transistors in the output stage, I have attached a photo with these marked, we have no idea what they are as the writing has been rubbed off. Link to photo on my website: http://dhost.info/wendyb/mission.htm

I had to use someone elses photo, hope you don't mind. Any help would be appreciated. Looks like we are hitting a dead end.

Many thanks
Wendy B : )
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Old 23rd January 2012, 12:22 PM   #2
homemodder is offline homemodder  Portugal
Account disabled at member's request
Join Date: May 2006
This is most likely designed by Stan Curtis, outputs are probably lateral mosfets 2SJ49/50 and 2SK134/135.

Google the name Stan Curtis, he has a webpage and I think he even has the schematic on the site. Look for mission 777, compare the circuit to your amp circuit, likely the same. Hell be able to help you if you mail him, very friendly nice guy.
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Old 24th January 2012, 07:06 AM   #3
Wendyb is offline Wendyb  United Kingdom
diyAudio Member
Join Date: Jan 2012
Location: Norfolk, England
Thanks for your reply homemodder. I think I will try emailing Stan, as if he has time to reply, could be very helpful. We had a look at the Mission 777 on Stan's website and it wasn't anything like the 778 inside, although some parts may be similar.

Not sure if it was Stan who made the Mission 778, as I don' think it is mentioned on his website, all I know is it came out around 1984. Thanks for the mosfet numbers also. Will post how I get on, as it may help others.

Kind Regards

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