[TechAssist] Re: Pioneer Power Amp OUTPUT MODULE Shorts ASAP
- From: peggs <peggs@xxxxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx,".TECHASSIST @ freelists . org" <techassist@xxxxxxxxxxxxx>
- Date: Tue, 04 Nov 2003 09:01:37 -0800
I have the M-790 manual,what's your fax # ???
The PCB's(front and rear) including the outputs can be purchased from
Pioneer if they are still available. 800-457-2881
Front rwz3697, $33.54
Rear rwz3698, $33.54
Remember to always discharge(bleed resistor)
the B+ and B- Voltages when your turn it off.
Manual says before performing Idle Current or operating Temperature
of Fan Motor adjustments,
Short the Blow Trigger Shorting Pin (CN7504 AKC-113 Blow Trig) of
the Front Assembly to prevent the protection IC from malfuctioning.
Peggs
At 10:31 PM 11/3/03, Bil Green wrote:
>Pioneer M-790 (and many other similar models)
>Audio output transistors (6) shorted
>
>Need the procedure to disable the Blow Trigger circuit so
>the new outputs will not be ruined during testing. I don't
>want to replace the module or boards, due to the high
>repair bill.
>
>
>These Pioneer power amps contain the output transistors
>within a cube like circuit boards/ heat sink/ fan assembly.
>
>And if it even thinks that something is wrong, it is designed
>to pop the output transistors, and thus blow the fuse. Someone
>should go to jail for this dirty trick.
>
>"The action of the "Blow Trigger" line is to INTENTIONALLY blow
>the outputs, so that the fuse will blow. It is a resistor ladder
>arrangement, the summed output of which is zero volts under normal
>conditions.
>
>Interestingly, DC offset is NOT monitored. If any of the supplies
>sags, the sum is no longer zero, and the BLOW line goes to .6volts
>or so, at which point the bias is slammed HARD. For example a bad
>cassette motor will cause the outputs to blow.
>
>There are surface-mount transistors which can be shorted base-
>emmiter to defeat the BLOW line for testing purposes."
>
>
>--
>Best regards,
>
> Bil Green
> 2001 TV VCR
> Mammoth Lakes, CA 93546
> 760-934-2001 mailto:tv.vcrrepair@xxxxxxxxxxx
>
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