Advice/guidance on reusing the power supply & power amp module from the Onkyo TX-875

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Advice/guidance on reusing the power supply & power amp module from the Onkyo TX-875

I've Finally decided to start stripping the rest of my old Onkyo TX-875 that's been sat in the shed partly dismantled for ages for any reusable parts however the only issue was the common HDMI fault and i did try getting it to work with I2s digital input however could never get it to work as a system, i learned a lot from experimenting with the digital DAC board from the unit with a Cubietruck SBC providing 4 stereo I2s input's however once it was put into the amplifier the system processor would mute all audio and what ever else that stopped the audio signal getting from the DAC to the power amp,

anyway upon starting to take it apart i noticed the complete power supply and power amplifier is one complete unit and for what i can tell quickly looking over the power supply and power amp board's and also looking at the service manual it should't be to difficult reuse as a complete unit

there's a couple of relay's to control the power, both main's to the primary and a couple from the secondaries to the power amplifier for B+ and B- also
Relay's for each each speaker output plus 15V+/- regulation on another board and then 7 line level input's and everything look's pretty easy to understand and modify into a 7 channel power amp to use with another pre amp the only thing holding me back is my lack of understanding of the protection circuits as there's fan control with sensor's on the heatsink's to work out but more importantly there's a Protect line coming from some transistor's fed from the IPRO and VPRO line's also another called VOLH from the power amp,
Question 1,
am i correct in thinking two of them is for over current and another over voltage sensing ?
dose one of them detect DC on the amplifiers output
Question 2,
how can i best reuse these signal's and use them to continue to help protect any speaker's connected as they appear to go straight to the processor unit and will have to test everything with the multimeter to check the voltages involved ??

any advice would be gratefully received as there's nothing wrong with the power supply and the main amplifier stage and it's a beast i would like to be able to make use of in my future project's and there's only my lack of understanding of the 3 IPRO, VPRO & VOLH control line's really stopping me so any guidance at all would be gratefully received,

thank you
 
Has anyone got any information regarding the IPRO and VPRO line's also the other one called VOLH from the power amp please ?

is the IPRO the current sensing ? what dose it do please ??
is the VPRO the voltage/power sensing on the speaker output as it comes from the speaker output's and passes through a 47K resistor ??
and the VOLH for sensing DC on the speaker's output because it's connected to the speaker output and passes through a 1SS133 diode and 47K resistor ??
the service manual is here and it's on page 17/18

https://www.manualslib.com/manual/1064234/Onkyo-Tx-Sr875.html?page=4#manual

please could anyone give me any information at all as this is just as much about learning as it is about getting this working

cheer's
 
Also would anyone with experience of working with the 2sa1962 / 2sc5242 output transistor's please advise,
The power amp uses 2 pair's on each channel,

So here's what i'm thinking, I'm interested in finding out if it's possible to modify it and use two or even three of the channel's output stages (2sa1962 & 2sc5242) in parallel like they do with a lot of the PA amp's by using multiple output transistors in parallel with 0.22 ohm resistor's ect which the power amp board already has for increased output using a singular driver board making a more powerful channel to drive a subwoofer and leaving 4 channel's to bi-amp a stereo pair of speaker's

please check the service manual page 15/16 as i would like to know if,

would it work if all the 2sa1962 base lead's are connected together and also all the 2sc5242 base lead's connected with one driver board or would i need to inject the audio +/- signal from the driver board im actually using into the bases of the driver transistors on the other channel board's

if someone with the knowledge and experience could please look over the service manual and please advise on any of my question's and provide any guidance on moving forward please

I know it's a long shot but you don't know if you don't ask/try :)
 
Not digging deep inside this very complex 7 identical channel power amplifier, just thinking aloud:

1) you have seven 140W@8 ohm amplifiers, thanks God each one has its own personal input which makes them usable.

2) although in principle a single driver board might drive 2 pairs of power transistors, as easily it might not; even if it could supply drive current to more pairs maybe/probably the protection circuits would not like that, so that´s a stick in the wheel.

3) and it would increase power by increasing current capacity only, but not voltage capacity, so only way to profit from that would be to halve speaker impedance.
So you will still get 140W watt into 8 ohm, no matter how many transistors you parallel, and to achieve an increase you would need to find a 4 ohm 280W woofer.... or use 2 8 ohm woofers in parallel per channel.

4) given that, and wanting higher woofer power, I would drive 2 channels with exact same signal (inputs in parallel), each one driving *one* 8 ohm woofer, and mounting both in the same cabinet, which would be labelled "Left woofer".

Same with another 2 channels, now label that cabinet "Right woofer"

5) we are left with 3 channels.

Sadly even numbers are hard to split in halves, so I would use 1 of them to drive a smallish bookshelf speaker and call it "Main Left", assign another to "Main Right".

So now we have a stereo amplifier driving 2 nice compact cabinets, helped by 2 wall shaking double woofer cabinets ... not bad, huh?
And *guaranteed* working, plus not messing with (and maybe damaging) amp guts.

6) you have a spare channel left.

You may leave it unused, or if that is unthinkable (OCD? ;) ), feed it a mono mix and use it to drive a couple background music little cabinets somewhere else: garden, by the pool, kitchen, whatever.
With its own volume control of course.

I fear messing with such a beast guts (I shudder thinking about hair thin traces and minuscule pads) may leave you with a dead or at least lobotomized fine amp.
 
Thank you for your reply,

if you read my first thread I've actually stripped this amplifier down to it's core part's i want to use for this project, it's power supply section and power amplifier only taking out all of the complexity that makes this amplifier as a hole a nightmare to work on/modify and only want to use the power amplifier section (all the digital logic/processor and control circuits has been removed) and so i'm left with a bunch of 12v relay's to control power to the transformer's primary and a couple from the secondary winding's to the power amplifier, 7 more 12v relay's for each channel speaker's output then i've got 7 line level input's, 1 for each channel's driver board i'm wanting to use with another external pre-amp

HELP NEEDED >>>>>>>>>>>>>>>>>>>>>
My main challenge/learning curve of building my own protection circuit and learning how to implement that using the IPRO and VPRO line's also the other one called VOLH from the power amp as at the minute there isn't any and i'm yet to try if in fact the amplifier will work without it for testing purposes until i've found a way to implement my own protection circuit to control power and speaker output's and need support and guidance in doing this,

If you check the service manual using this link you can see how the 3 IPRO, VPRO and VOLH are connected to the amplifier, now it appear's to be pretty much the same as i've seen in other service manual's when repairing them however they appear to all call the signal lines something different (which seem's a common theme)

IPRO appear's to be linked to the bias current through a 2SC2240 transistor, bias is on it's base and the IPRO is connected to the collector and 33K resistor

VPRO is connected to the speaker output through a 47K resistor

and finally VOLH is also connected to the speaker output and first go's through a 1SS133 diode and then a 47K resistor

https://www.manualslib.com/manual/1064234/Onkyo-Tx-Sr875.html?page=16#manual

you can also see on page 16 how the 2 2sa1962 and 2 2sc5242 output transistor's are set out in parallel and going back to page 15 will show you the driver board's for each channel and there all identical,

and my last challenge is see if it's possible to....
there is already 2 pair's of 2sa1962 / 2sc5242 output transistor's on each channel however i'm interested if it's possible to drive 4 pair's of 2sa1962 / 2sc5242 in parallel from the same driver board and run them in parallel for better current handling for driving a 4 ohm subwoofer however that appear's to be just something im going to have to try and see if it work's as the protection circuit is the more important thing to work out

Cheer's
 
Got The Power Supply and Power Amplifier Stage Working !!!!!

Turn's out the audio input stage is really sensitive even on really low volume it kick's out pretty high volume level's

as i now have the power amp stage WORKING with just the power supply and power amplifier my only issue left is there's no kind of protection what so ever apart from fuses

I now need the help, support and guidance to implement my own amplifier protection circuit for the powers supply and speaker's ?

are there any good thread's people can provide link's to or solution's for monitoring the power supply for dead short's ect and also bias current and DC voltage on the speaker output's please ???

i'm really exited about getting this monster of a project finished now and making a multi channel power amp out of it to use with my Yamaha AVR receiver using the preamp out's for driving my front stereo pair of speaker's using 4 of the channel's for true Bi-wiring for my monitor audio main speaker's and using another for my monitor audio subwoofer which is now passive thank's to a failed power supply (Hence me asking if i can use 2 of the output stages in parallel as the subwoofer is 500W RMS @ 4 ohms and looking at it the modification is easy to do however i'm yet to try it to see if it work's and something that can wait till i've got a mean's protection

Please any help what so ever, it's now just like any other project amp and how do i make a protection circuit and impalement it to protect the power supply and speaker's please ???
 
Someone please, i only need advice on one thing, I've got it working and just need to know how to implement a protection circuit using the "Protect" & VOLH signal lines that would normally go to the microprocessor to trigger the relay's for the power supply and speaker's to be able to use this in my next project ?

PROTECT pin - dose the microprocessor look for this signal to be pulled high or to ground on this pin or a voltage/current change if there's any issues to put the amplifier into protect ?

VOLH is this for the DC speaker protection or excessive volume protection as it comes from the speaker output through a 47K resistor and a diode letting DC positive voltage to flow then a couple of resistor's and a diode to ground them to the microprocessor so dose it look for a DC/excessive voltage on this pin before triggering the speaker relay's ?

I just need to know what i'm looking for on these 2 sense wires from the amplifier to make my own protection solutions so please help ?



Why isn't there more interest in this beast of a power amplifier module with 7 really high quality individual channel driver boards each driving 2 2sa1962 and 2 2sc5242 with genuine output transistor's and a huge high current power supply as there showing up really cheap all the time for spares or repairs with no audio due to HDMI board issues or going into protect and even if one channel's gone down it still leaves 6 which would still leave it a great project to drive a pair of 3 way speaker's with active crossover and another preamp as i will be documenting what and how to reuse this great 7 channel power amplifier and power supply for people in the future to work from and use in there own project's
 
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Here's some pictures of the service manual covering the main part's im using, hopefully it will help....

here's the circuit layout from 1 of the 7 identical driver board's, please note i'm wanting to know if/how i can possibly use the IPRO & VPRO and VOLH sense lines for building my own protection circuit

https://www.dropbox.com/s/ngkt81vhy2gphu1/Onkyo TX-875 Amp Driver Board.png?dl=0

Here's the circuit layout of the X2 2sa1962 and X2 2sc5242 output transistors

https://www.dropbox.com/s/l758lcp3d...stors 2SC5242 & 2SA1962 layout board.png?dl=0


and here's some more covering the rest of the IPRO, VPRO & VOLH sense lines and also power and temperature sense and control lines also power relay's for B+/B- from secondary winding's also the 7 line level input's

https://www.dropbox.com/s/wrcdfp5bx1lj0y0/Onkyo TX-875 Power Supply and protection board 1.png?dl=0

https://www.dropbox.com/s/amml26symaoumpf/Onkyo TX-875 protection IPRO, VPRO & VOLH.png?dl=0

Please could anyone have a look over them for me and give any advise,

please let me know if you can't load the pictures
 
Think i'm just going to settle for fuses in the power supply and standard DC speaker protection board's you get cheap from china in order to use it safely,

Would anyone with experience paralleling output transistors just check this out for me please,

here's a link to the pic of the driver board and i'm interested in knowing if the 6 pin connector to the right of the pic that connect's to the circuit with the main output transistors and is shown on the link below that would be safe to connect to another channel's output transistor's using the same 6 pic connector and joining both speaker output's together and running them in parallel for the higher current and driving a 4 ohm's load please ??

Driver board...
Dropbox - Onkyo TX-875 Amp Driver Board.png

The output transistor circuit layout...
Dropbox - Onkyo TX-875 Power Amp transistors 2SC5242 & 2SA1962 layout board.png

Yes there's questions if the drivers have enough current to drive 4 pair's of 2sa1962 / 2sc5242 unless someones got any ideas of modifying the second driver board to keep both in perfect sync in order to drive the output transistors in parallel,

My idea was to cut the traces on the second driver board at the bases of Q6036 & Q6046 and (inject/modify) drive the transistors with exactly the same signal coming from the base of the driver transistors on the driver board im actually using to provide the extra current to drive the extra 2 pair's of 2sa1962 / 2sc5242 and joining the speaker output's together to run them in parallel ?

can someone please give thoughts an advice please ?

cheer's
 
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I've got the modification for extra current to drive lower impedance load's by using 2 channel's now using 4 pair's of output transistors in parallel working by connecting the same 6 pin connector for the output transistor's to the next channel removing it's driver board and connecting pin's 2,3,4,5,&6 from the used driver board still in place to also drive the second channel's 6 pin connector and joining the speaker output's together, (still got to get my scope out to check for any crossover distortion) but there was only 38mvdc on the speaker output even on high volume level's and sounded OK on my simple test rig with old speaker's

Hope that's clear enough for anyone in the future looking to do any similar modification's as it's the main reason for documenting this build,
People seem to be really good at buying kit's and following instruction or placing pictures stating look what i've build but few actually seem to document or modify/reuse savaged part's compared to the actual number's of people using this side or there's a lack of support for people doing so on here,
anyway

So moved on to finish the power supply modification's but unfortunately i was wrong about the Onkyo transformer it appears to have 3 secondary winding's providing 3 different voltages to the amplifier stage all split rail out, +/-24Vac Gray Wires, +/-33Vac Yellow wires and finally +/-48Vac and a common black wire centre tapped rail coming from the transformer and the +/-24Vac is hard wired straight to it's own rectifier then to the B+/B- of the amplifier,s reservoir capacitors, then the +/-33Vac is controlled by 2 relay's again going through it's own rectifier before connecting to the same B+/B- of the amplifier,s reservoir capacitors and the same is repeated for the +/-48Vac with it's own pair of relay's and rectifier before connected to the B+/B- of the amplifier,s reservoir capacitors,

would this be used when you set the speaker's ohm's rating's or required power power output and how do i stand having all 3 supply's connected at once for extra current as that's what's thrown me all being different voltages and the lower +/-24Vac supply is constantly connected and the other two are relay controlled ?

Scrap's my idea of using the different winding's to power different channel's for left and right as i wrongly presumed they was all the same adding up to more current output capability however what's peoples ideas on using this setup with 2 higher controllable voltages to power 4 channel's aimed at Bi-amping a stereo pair of speaker's and i'll just add to the already 18'000uf reservoir capacitors and drive the remaining modified channel's run in parallel from the separate +/-65Vdc power supply
would this be of any use in my application ?

i may just use a 3 way switch on the rear of the enclosure once i've found one for power output rating of Low, Medium and High output wattage because that's the only thing i can think of doing with it ?

Any ideas please ??
 
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in fact with more deeper investigation with a test meter it appear's to be different tap's of the same secondary winding providing different voltages controlled by relay's,

any idea's why ? benefit's of doing this please as it's the first time i've come across it in a project where i need a basic understanding of why and how best to use it if at all ?

would it serve at providing different wattage output's into different load's ? 4-8-16 ohms

cheer's
 
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here's more info for anyone in the future,
connection P7210A is a 9 min connector on the far left of the amplifier board and went to the microprocessor/control board and so far i've worked out when supplying connection JL6900A with 12v from the speaker output board that,

Pin1 FANCTRL requires high logic signal (i think as haven't tried it as going to provide my own temperature control circuit to control the fan's better
Pin 2 SEC1M Requires pulling to ground to activate the relay's on the adjoining power supply board to use the +/-33Vac supply
Pin 3 SEC1H Requires pulling to ground to activate the relay's on the adjoining power supply board to use the +/-48Vac supply
Pin4 VOLH go's high to 13vdc unloaded ?? can't think of anyway of testing this so may just leave it as i don't need it,
Pin 5 PROTECT this is interesting as after a small period of time this go's high to around 16vdc (anyway to test if this senses DC on the speaker output's without damaging the amplifier ? thought about just supplying the required 12v and disconnecting the B+/B- power supply to the amplifier and applying a couple of DC volts to the speaker output and seeing it's reaction ? hopefully it cut's out the 16VDC supply so i can use it to switch the speaker relay's and use it as intended

Pin 6 THERMAL_2 both from the heatsink thermal sensors
Pin 7 THERMAL_1 both from the heatsink thermal sensors
Pin8 +3.3VDG power supply to the thermal sensors
Pin 9 GNDDG ground for the thermal sensors


Connection P5000A is the line level input's for each of the 7 channel's

also each speaker output from each channel, the common negative are the wires from the base and each positive comes from between the vertical driver boards

I've left NAPS-9040 power supply board in place with fuses and relay's that deal with the secondary winding's from the transformer for the amplifier and i may also be reusing the speaker output board as it already has the 12v power supply for the PROTECT circuit and fan and just a bunch of relays to control for each speaker output however if i don't get anywhere using Pin 5 PROTECT i'll just use the general speaker protection board's off eBay,

I've got this great power amplifier working by stripping it down, see pic..

Dropbox - Onkyo TX-875 amplifier 1.JPG

and

Dropbox - Onkyo TX-875 amplifer 2.JPG

applied main's power directly to the primary winding of the transformer and bridged the top pair of relay's on the power board to provide power to the amplifier and checked the voltages specially looking for any DC on the speaker output's and then applied a line level signal from another preamp with volume control to connector P5000A that you will find central to the board in front of the big cap's and used pin's 1(+) and negative/ground to pin 2 for testing purposes that will use the surround left channel, the right most driver board and connected an old speaker, and the other channel input's are on pin's 3,5,7,9,11,13 as they go from right to left, the wire coming from the base is negative and the one coming from the board fixed to the heatsink with the power output transistor's on for that channel is your speaker positive,

it was possible to use the amplifier like that however if had no protection apart from fuses on the power supply
 
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