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Denon S-301 Malfunction

Claudel Filion

Jan 14, 2018
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Jan 14, 2018
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Hi there !

I have a Denon S-301 that has stopped working , when pressing the on/off button, the blue led light around the button starts flashing repeatedly and nothing works. Suspecting one of the several power outages in my area during windy weather to have something to do with all this.

I have read on this issue and checked my two speakers and subwoofer internal resistance, no short circuit.
-Tried performing the ''hard reset'' and issue persists.
-Decided to carefully open the device to look for anything obvious , i.e. : burnt fuse, visual defect on PCB... etc... none was found.

I am an automotive technician with decent understanding of electronics, but yet not a lot of experience.
I would really like to find a way to diagnose/fix my Denon unit(and learn at the same time ;) ! )because it is immaculate and i don't wanna trash it.
-I started checking how everything is supplied through the voltage transformers , supply to the 2 125v fuses, etc.
-I heard of possible ''output transistor'' failures, and i have found one of 2 fuses not being supplied, suspecting a specific transistor base not being triggered on one the Subwoofer unit PCB, where the supply units are.

Would anyone be kind enough to help me find a solution for this problem , or maybe have access to Denon Wiring schematics
for this specific unit ??

thanks in advance,
Kind regards,
Claudel
 

kellys_eye

Jun 25, 2010
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Testing the supplies is the usual first point of 'attack' and, in the history of potential fault symptoms, dried electrolytic capacitors in the power section are a good place to point at suspects.

Post some clear, close-up pictures of the power supply section. You can sometimes 'see' the defective capacitors by recognising a 'bulge' on the top of them.
 

Claudel Filion

Jan 14, 2018
7
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Jan 14, 2018
Messages
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Thank you very much for sharing your knowledge and thoughts with me !
I have checked most of the ''cylindrical'' capacitor types and could not find a visual flaw, same as for the other types of capacitors. I have attached a few pictures of the main power supply board , some with details of ''my findings'' !
Again what i wrote there might not be a defect , this my quick perception of what i found while taking a few voltage drop readings with a live circuit. Maybe that transistor i am talking about not being triggered, might be a consequence of something else as well...failsafe mode or something !?!

All i know is that F902 is not supplied with any power, and following the power supply logic evolution through the board seems to stop at TR902.

Also , in the section shown of picture 118, the last part of the circuit supplied is the collector of TR902( 9.33v) from JV12.

-Picture 116 with details of Fuse 902, left and right side of fuse.

I don't know if this will help , but trying does not hurt... they say !

let me know if you have further questions or inquiries !!

thanks a ton
Claudel
 

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Claudel Filion

Jan 14, 2018
7
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Jan 14, 2018
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wow this is a truck load of relevant info, i looked for documents online... probably did not search hard enough !!
Currently overviewing all this , and patiently waiting for your reply ! thanks
 

Claudel Filion

Jan 14, 2018
7
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Jan 14, 2018
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The full technical manual is readily available here:

https://www.manualslib.com/manual/1185943/Denon-S-301.html

which I suggest you download and we can discuss the rest of the procedure by reference to it.

Hi there, sorry for the delay, but i think i might of found something !!
If you go to page 201 on the pdf document and look around the transfo T901, in particular the ceramic capacitor C935( light Blue ).

Looking at the wiring layout, i think i should have voltage on both sides of that capacitor !?(correct me if i am wrong).
I have 11.5 V AC on one side and nothing on the other side of it ( testing live ) . Also comparing that capacitor visually to the others that have the same rating on the pcb... it looks like there might be a ''buldge'' on it, kind of a bit thicker or deformed..

let me know your thoughts on this,
thank you in advance
 

Tha fios agaibh

Aug 11, 2014
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Maybe that transistor i am talking about not being triggered, might be a consequence of something else as well...failsafe mode or something !?!
All i know is that F902 is not supplied with any power, and following the power supply logic evolution through the board seems to stop at TR902.

The role of tr902 is to switch on the relay feeding power to f901. Do you hear the relay click and do you have AC power at f901?
If so, I would suspect the primary of t901 isn't getting fired (by pwm). This is controlled by ic902. I don't know it's specific function but it's looking for the proper feedback via ic906. It's worth mentioning that photocouplers are a common part to fail in switch mode power supplies (what this is) but it certainly could be something else.

It could be that it's shutting it down because it senses a overload downstream or something like a failed diode or cap in the nearby circuit.

Be aware that dealing with high voltages in a smps can knock you on your arse. So be careful.
 

Claudel Filion

Jan 14, 2018
7
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Jan 14, 2018
Messages
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Good evening Tha fios !

many thanks for your time and interest in my case !!

Sorry for the delayed reply, last week-end i have investigated a bit more into my issue ( everytime i have a bit of free time i try to resolve that problem...) .

I have figured out that i have to trace my voltages in the '' 2-3 second window '' before the unit goes into failsafe ( pure logic ).
I have progressed a lot further into my problem, but the challenge is to find who is causing the failsafe, like you also mentionned.

-I have measured, first of all, the ''internal/total'' resistance of the unit via the A/C supply cord (without a/c supply of course ) :
approx 1.075 kohms.

-Then i have measured the resistance between the line and chassis/the neutral and chassis :
both approx 2.240 mohms.

On the SMPS supply board ( page 201/202 ) , looking up at my inputs/ouputs connectors :
( CY041/CY043/CY071/CY101) :
-All the grounds are ok ( very low resistance in regards to the chassis, 0.2 ohms ) .
-Most of the +/- votlages(DC) are there, very close to the specs written at each pin(only present for 2-3 seconds) ,

EXCEPT FOR :

- CY071 : pin 1 : +12V : 11.77 V
pin 5 : limit + : 5.9 V
pin 7 : limit - : -6.25 V ...(i am not sure of what i should be reading for limit +/-)
- CY101 : pin 7 : power_down : 0.860 V steady (does not change before or after failsafe, also present with unit in standby)
pin 8 : On/Standby : 3.1 V
pin 9 : +5v_NSW : 6.3 V steady ( does not change before of after failsafe, also present with unit in standby )
pin 10 : C_sens : nothing here (12mv) steady ( does not change before of after failsafe, also present with unit in standby, also unsure of what C_sens stands for... sensor ?? ).

at this point, if your knowledge could help me progress further, that would be awesome !
Also if you have any tips on how to check transistors or diodes in continuity or ohms ( i know it is harder to diagnose when they are in a circuit ) .

let me know your thoughts,
best regards,
Claudel
 

Tha fios agaibh

Aug 11, 2014
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Hi Claudel, Glad to help if I can with what little knowledge I have.

A couple of things; I wouldn't be looking at total resistance as it's not much help at this point.
When measuring voltages, measure with respect to related ground pin.
Example; cy041 pin is +31v with respect to pin 3 or 4 which is Gnd_P. This reference point may be different than Gnd_A or chassis ground. May sound like like nit picking, but the devil is in the details.

I'd start by checking all major voltage supplies and look for major dips. I would expect roughly -5% to +15% of the expected voltage. So, 11.8v on pin 1 of cy071 (with respect to pin 2) is probably fine. As far as pin 5 (limit+) and 7 (limit-) also on cy071, I'm not sure of its function. It looks like a regulator circuit in the smps that steers the voltage + or - based on feedback from ic501,502 and 503 (p205) which are presumably comparator circuits of the audio polarity. There's only 1/4v difference between limit+ and limit- so I wouldn't be too alarmed by that.

Then, I would take a close look for burned or swollen components. Sometimes a discolored component can flag you to the vicinity of a shorted component.

I'm confused why there seems to be the same circuit on page 201,202 and 203.
Do you have more than one smps?
 

Claudel Filion

Jan 14, 2018
7
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Jan 14, 2018
Messages
7
Hi Tha fios,

i couldn't agree more with you, everything is in the details !! I have double checked and the readings are all the same with their respective ground points.

thanks for the inputs and clarifications, will keep that in mind !

As far as voltage tracing, before i proceed further on the AMP unit board for exemple, i was trying to understand a bit more the '' power_down'', on_standby and C_sens as their nominal value are harder to evaluate...

-I suppose that ''power_down'' with a steady voltage of 0.860 v isn't really alarming, and since there is no change on the value, i suppose i can set that aside for now ( still unclear to me...what do they mean by power down exactly)?!?
-As for the on_standby value, at least on this one there is a reading that makes sense with the symptom, but i don't know if the 3.1V is what i should read there before the failsafe takes place ?
-And then, the C_sens is the one that really throws me off, no reading there at all... maybe normal, maybe not, maybe some sort of circuit to indicate if there is a fault for a sensor or whatever feedback...i need to dig in further here.

I did a close visual check a few times, the SMPS and AMP board and their components are looking fine to my ''unexperienced'' but pretty accurate eye. The Receiver unit is harder to evaluate due to the complexity of more refined electronics, but from what i can see, i could not see anything obvious standing out, i might have to completely strip the receiver apart at one point, but then it will be hard to diagnose it in a dismentled state.

Page 201/202/203 is because there is 3 types of Denon s301 ; E3, E2 and JP models.
My SMPS board has ''E3'' stamped on it so we need to focus on page 201.
Sorry, i should of mentionned that earlier.

Thank you very much for your time, and please correct me where you think i am wrong.
I would like to have your opinion on the 3 circuits i mentionned ealier, would be appreciated.

I will try to spend more time on it this week end and will update my findings accordingly.

kind regards,
Claudel
 

Tha fios agaibh

Aug 11, 2014
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I don't have time to get too in-depth, at least at the moment.

I still say your better off looking for the vital things like voltage checks first.

I'd guess "power down" is a input or bus to the processor to systematically turn off things in a safe maner.
If your still curious, look at pin 17 of cx201 on page 195 that goes to "audio" and try and find where it goes.
If there's descrete components its function can be figured out, but of course dealing with a digital processor you'd have to know the intricacies of its program to know how it works.

There are details about the chips and their pins in the pdf. that should be a big help if you get to that level.
Happy reading and probing.
 
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