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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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23rd Sep 2022, 10:16 am | #1 |
Pentode
Join Date: Jan 2021
Location: Hinckley, Leicestershire, UK
Posts: 119
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Testing STK4142
I have this module out of circuit for testing, from a Denon RCDM38 which is in protection mode, its the most likely failure point.
Pin 9 -VCC Pin 10 RC out Pin 11 +VCC Pin 13 LC out Testing resistance across these pin the results are 11&10=15MOhm 11&13=15MOhm 9&10=15MOhm 9&13=OL Which suggests to me that -VCC to LC out is blown. Am I correct or should I be testing other pins? |
23rd Sep 2022, 12:18 pm | #2 |
Pentode
Join Date: Jan 2021
Location: Hinckley, Leicestershire, UK
Posts: 119
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Re: Testing STK4142
With the amp board completely disconnected its still in protection mode, so I am guessing power supply.
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23rd Sep 2022, 7:17 pm | #3 |
Dekatron
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,670
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Re: Testing STK4142
If the amp is in protection mode finding out why will help diagnose what possible circuits to test further. Depending on the protection circuit used and it's complexity they mostly work by detecting DC on the output. DC on the OP could be caused by various things, shorted OP transistors or in your case shorted power amp IC, leaky caps etc.
A good point to start is to check for DC on the speaker OP. Andy.
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24th Sep 2022, 1:54 am | #4 |
Pentode
Join Date: Jan 2021
Location: Hinckley, Leicestershire, UK
Posts: 119
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Re: Testing STK4142
The amp board is disconnected, so there cannot be any DC on the output. Its the testing of the STK I am not sure about. If I can get a pass result then move on to other circuits, if it has failed I will probably bin it. This is a micro HiFi with 9 boards crammed inside. It had a favourable review on What HiFi so thought it worth a look.
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24th Sep 2022, 7:06 am | #5 |
Octode
Join Date: Feb 2007
Location: Ely, Cambridgeshire, UK.
Posts: 1,976
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Re: Testing STK4142
last time i had a STK i was not sure about i brought one off these
https://www.ebay.co.uk/itm/262935943...Bk9SR67qyuHtYA and then built it up as a test bed with the supect STK |
24th Sep 2022, 7:08 am | #6 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,580
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Re: Testing STK4142
...not forgetting the protection circuit itself! I was caught out once by a protection circuit that had actually failed. In desperation, I disconnected the protection circuit to 'see where the smoke came from' and to my surprise, everything started working (into dummy loads I hasten to add)! It was a s/c transistor in the protection circuit.
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26th Sep 2022, 12:47 pm | #7 |
Pentode
Join Date: Jan 2021
Location: Hinckley, Leicestershire, UK
Posts: 119
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Re: Testing STK4142
I think I may have found the problem. Unit stripped down to test transformer. There no is continuity on the primary winding, the red and black going in.!!!
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27th Sep 2022, 10:04 am | #8 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
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Re: Testing STK4142
That could be easier to sort than sourcing a decent STKxxxx!
(Though it's always possible that a blown STKxxxx might have cooked the transformer in the first place )
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28th Sep 2022, 12:08 pm | #9 |
Hexode
Join Date: Dec 2020
Location: Raunds, Northamptonshire, UK.
Posts: 359
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Re: Testing STK4142
If that is so the amp would not even have gone into protection mode.
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Graham |