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JBL PRX 712 - Help!

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Earplug View Drop Down
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    Posted: 14 February 2018 at 11:18am
I´ve got a prx 712 amp module here that someone has "had a go at" and is missing some components.  Confused

Namely:-  T501, T505, T508, D500, D503, D505

Anyone have the schematics, or able to identify the missing bits. At least that would help me get started on the thing. The preamp module is still working, so I´m hoping that it is not totally beyond salvation.   Smile


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Post Options Post Options   Thanks (0) Thanks(0)   Quote doctor Quote  Post ReplyReply Direct Link To This Post Posted: 16 February 2018 at 8:19pm

In the PRX712 powered speaker the S-PRO2 digital power amplifier is used.
Pascal Audio Company from Denmark makes this module. Very, very unreliable device.
The fact is that, in addition to the missing elements, you will need to replace many other elements (mandatory: IC500, IC504, IC505, T503, T506, T509, OC500, OC501, OC502 and many other if it is necessary) and this is not a guarantee that the device will start working.
I really do not recommend repairing it.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 17 February 2018 at 1:09pm
Ok, thanks for the heads up.

I do know how bad they are, but replacement boards are stupidly expensive. A friend bought 12 of these of which 3 blew up fairly quickly. Fortunately the problem was just the the TVS diode (D522) - maybe a bad batch, or design fault? It´s just trying to replace parts that aren´t there is a bit impossible - and getting hold of some schematics would help as well...    Ermm

Since posting, I have had a closer look at the board and noticed at least one discoloured IC (not sure of the number - 8 pin device between C504 and C506), so - as you recommend, will most probably pass on the repair.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote doctor Quote  Post ReplyReply Direct Link To This Post Posted: 17 February 2018 at 1:58pm
Defected D522 (TVS diode) is the simplest defect, which arises due to external overvoltage. As a rule, a board remains intact. Unfortunately, most boards are damaged due to internal reasons.
A method of fixing a board paying attention to discolored or blackened components is ineffective, especially for complex digital boards. In order to repair such board one need to know how SMPS and digital power amplifiers work.
The simple example: discolored IC505 chip is the IRS21867S (MOSFET driver) - very simple chip.You need to read its datasheet and you must understand this so that you can explain its work to someone else. Try. Are you ready?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 17 February 2018 at 5:14pm
Ok, thanks for all the advice, but do you have the schematics? Then let me worry about figuring out how the thing works!   Smile


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Post Options Post Options   Thanks (0) Thanks(0)   Quote doctor Quote  Post ReplyReply Direct Link To This Post Posted: 17 February 2018 at 6:36pm
Pascal Audio does not disclosure schematics even for authorized laboratories. Their repair policy provides only the replacement of the complete module.
I do not have these schematics. I fix such modules without schematics.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 18 February 2018 at 12:48pm
Yes - just what I suspected. So much for building a more sustainable world! And why it´s better never buy crappy self-powered cabinets. From what I´ve seen, even the Crown plate amps JBL are now using aren´t that reliable either - especially in the heat we get down here.   Ouch  Unhappy  Ouch


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Partyson Quote  Post ReplyReply Direct Link To This Post Posted: 04 May 2019 at 10:04pm
a little bit late, but here is a list of parts that I replaced and everything earned the first time, some replaced by the closest analogues that were in stock
IC505
IRS21867SPBF /INFIN /SO8

T501.5.8
STF21NM60ND/ST/TO-220F

IC500
UCC2893D /TI/UTD /SO16

most likely burned out resistor R507 (10 Ohm)

I will be grateful for the hint which transistor is installed T511
he is feeding IC500 UCC2893D
Thank!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 05 May 2019 at 4:17pm
Ok, yes - been a while.

Thanks for the parts ID.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote doctor Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2019 at 2:23pm
T511 is the BC857B.

T501,T505, T508 are the STP26NM60.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Partyson Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2019 at 12:37pm
thank you so much for the tip!  The question on T511 is the transistor of the PNP structure, but on the base it has the same voltage as on the emitter and it is constantly closed, pressing the standby button does not change the situation.
There is still some kind of malfunction, and this is not a dual transistor that controls the base t511, please give a part of the circuit of this chain
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Post Options Post Options   Thanks (0) Thanks(0)   Quote huanvojnito Quote  Post ReplyReply Direct Link To This Post Posted: 11 June 2022 at 11:12am
Hi Doctor!

I have an amplifier like this, and I am confused a little bit. Do you can help me please? I am not sure to identify some of the components for change in the motherboard

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