technics amplifier repair!!

[jamesie]

hi all , is there anyone in devon that repairs hifi , i have a technics se-a808 power amp that need a repair , the amp powers up , the internal relay does not click "on" so no audio , all fuses inside of the unit are ok,,help!! , its a shame not to repair it as i have the preamp and remote unit as well.

[istari_knight]

Do you know the history of the amp ? Did you buy it untested or were you using it when the fault occurred ?

The SE-A808 uses STK modules so there's not an awful lot to go wrong but when they do its expensive to fix... Replacement STK-1050's cost £22+ each & there's two of them...

[jamesie]

i bought it with the fault ,, it came with the pre-amp st-k808 and remote processing unit sh-r808 ,, my ebay bargain of the month £1.20 , it is all very clean and i thought if it was a cheap fix i may get it done ,, it has not been tampered with and is in very good clean condition , there is some discoulouration on the board around one of the small 3 pin transistors , was kinda hoping the stk units were ok, although i have found replacement sanyo units for around £7 each free delivery, at that price i could just order a pair and put them in see what happens

[istari_knight]

Can you post a picture up of the internals ? Would be good to see where the discolouration is.

Are you looking at getting the STK's from China ? Beware if so, every transistor/IC/Opamp I've ever bought from China has been fake...

[jamesie]

i have a pic on my phone , if you pm me your mob number i can send it to you ,, the STKs i found are from china :( they are on ebay although they are meant to be sanyo and the seller has 100 percent.

[istari_knight]

PM sent.

You could take a chance on the Chinese STK's... In defense of the Chinese sellers I've dealt with, they all apologised & gave full refunds after I told them they were fake [I'm sure they knew but if only 2/10 buyers complain its still profit I guess.]

Personally I would be inclined to keep the original transformers as they are good quality but replace the PCB with modern amp boards. There are so many available now it should be easy to find some that match the transformer secondaries.

[jamesie]

"ITS ALIVE":) a very big thank you to you james , i did as you said , fortunately i removed the offender first time ,only took about 15 minutes , plugged it in and the harmonious click of the relay was heard,:) plugged in the ipod as it has a volume control and there was sweet music , so that is only one stk that is down and had sent it into protection mode, exactly as you said, i made my choice of which one to remove first based on the fact that the right channel stk came away from the heatsink very easily , the left channel stk was rather hard to pull from the heatsink ,(i had to get a blade behind it) which i thought probably indicated "heat" , so should i replace both stk units or just the offender ?, i am thinking just the offender as the other channel is working fine ,no distortion ,hum or buzz. this is destined for my conservatory when i have built it later on in the year , it will be for an ipod based system with a small pair of monitor type speakers, which i havent purchased yet.

[istari_knight]

Result :thumbsup:

Yeah, just replace the knackered one, don't forget to renew the thermal compound when you fit the new one ;)

[RobbieGong]

James 'istari_knight, You are the man :)

[jamesie]

got the new stk1050 yesterday , as i had a few hours alone this morning i thought it a good opportunity to fit it , all went without a hitch , turned the amp on and click ,, over went the relay and it is working fine , thought i would check the dc output voltage as well ,so i got the meter out let the amp idle for 10 minutes , disconnected the speakers and source input , set the meter to mv setting and probed the outputs , left channel 5.5mv left channel 2.8mv , so all pointing to a good healthy amp , i have read anything less than 15mv is good and healthy and that slight differences between channels is quite normal. as long as you dont get readings over 50mv because that points to a problem looming , the reason i wanted to check this is that i purchased the replacement stk1050 from ebay and it arrived from china for £6.22 delivered (although it is meant to be a sanyo part), i had concerns that if it was a cheapo nasty fake part that it could be sending high levels of dc current to my speakers , but looks like all is well , i am very pleased ,
once again thanks james (istari knight) for the advice.:):):):)

[istari_knight]

Nice one :thumbsup: Sounds like you got a genuine part - Bonus ! Your quite right, DC offset under 50mv is perfect.