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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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12th Dec 2019, 4:36 pm | #1 |
Diode
Join Date: Dec 2019
Location: Galway, Connacht, Ireland
Posts: 3
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Technics SU-V4 no output
Hi all, (my first post)
This amp just cut out while playing a record through it not too loud. I replaced ic301 stk8050 (a direct short on pins 2&3). Protection circuit would still not kick in. I jumped the relay points on both channels ( bypassing the protection circuit )& get an output hum on the RH side (driven by ic3] but the LH side is still dead from newly replaced ic3. On checking v readings The main 48v + & - are ok, however pins 12 to 14 on both stk8050 ic’s are incorrect with pin 14 at 14v. Also ic303 a duel opp amp pin 1 is reading 14v even when isolated, p2 is 0v & p3 is 0.13v power to pins 4&8 is correct. Any help appreciated. Frankcla |
13th Dec 2019, 3:54 pm | #2 |
Diode
Join Date: Dec 2019
Location: Galway, Connacht, Ireland
Posts: 3
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Re: Technics SU-V4 no output
Hi
I’d just like to update my last post, more info, for technics amp su-v4 This amp just cut out while playing a record through it not too loud. I replaced ic301 stk8050 (as there was a direct short on pins 2&3). Protection circuit would still not kick in. I jumped the relay points on both channels ( bypassing the protection circuit )& get an output hum on the RH side (driven by ic 302] but the LH side is still dead from newly replaced ic301. The main 48v + & - are ok, however pins 12 to 14 on both stk8050 ic’s are incorrect with pin 14 at 14v. Also ic303 (an6552) a duel differential amp pin 1 is reading 14v even when I isolated it. p2 is 0v & p3 is 0.13v power to pins 4&8 is correct. Looks like one side of the ic is faulty? How does the protection circuit work & what components are linking to it from the output amps STK8050 Would appreciate any help here Thanks Frankcal. |
13th Dec 2019, 4:47 pm | #3 |
Octode
Join Date: Feb 2007
Location: Ely, Cambridgeshire, UK.
Posts: 1,975
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Re: Technics SU-V4 no output
the one note I have is to check Diode D311 if s/c or leaky will damage stk8050
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14th Dec 2019, 5:27 pm | #4 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,780
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Re: Technics SU-V4 no output
It's not the easiest circuit to follow!
Do you have a schematic of some kind for the innards of the stk8050? If you have +14v on both 8085 inputs could it be the -16V line is down? Power supplies common to both halves? John |
18th Dec 2019, 3:57 pm | #5 |
Diode
Join Date: Dec 2019
Location: Galway, Connacht, Ireland
Posts: 3
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Re: Technics SU-V4 no output
Thank you both for replies
All supplies are OK 16V and 48V both + and - I now suspect IC303 is faulty on the pin 1 to 4 side as pin 1 reads 14v even when it’s disconnected and does not change state when I tie the input pins 2 & 3 togeather. When I repeat this on the other side (2nd dif amp output pin 7 changes state. This ic seems to control both IC301 & IC303. I will order a replacement and hope it works? |