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4 x HH M900 Mosfet:4 x Hotspot on driver PCB.

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Akino View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Akino Quote  Post ReplyReply Direct Link To This Post Topic: 4 x HH M900 Mosfet:4 x Hotspot on driver PCB.
    Posted: 16 March 2008 at 1:14pm
At this moment,i've 4 HH M900 Amps for repair.
besides,there's in the past,made some bad repairs.The fans and sensors was one of the wrong repaired things.

All the driverboard's have heat damage,..one is allready beyond repairs (just the PCB),the others are slowly burnigs temselves to death.
Is this just a desing flaw??Does't indicates there's somting else very wrong.
They become verry hot,...85 C + ,place a fan on them and they stay cool.
I've thingking of resolder them on the other side of the PCB,so they are cooled bij the airflow of the fan.
Now they are in a windless corner,at the base of the amp,with the PCB on top,so all heat rises into the PCB.

I've read also on this forum,about the old C-audio (en all the others A.K.A. mosfet UK Amps)
The desing is inside almost the same,so i assume that the issue with the 48V relays and the big 50 watt resistors is just the same here,as in all the other amps based on this desing .

I've started with almost no technical information,so i've disassambeled one amp,...as a reference for the others.

Is it correct to meassure the bias by this amp between te P and N channel,at the resistors ,point?


I've made some pictures,to illustrate the "hot spot" on the driverboards.

Burned out

XXXL size image


XXXL size image


XXXL size image


XXXL size image

On a road to hell



How not to secure the speaker terminal XLR (

one of 100 stupid things i've encounterd in the 4 HH Amps,..soldering the bias and offsetpots

The test and reference setup (and self education,)

XXXL size image

This setup is working fine,..


Edited by Akino - 17 March 2008 at 1:55pm
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Monitech View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Monitech Quote  Post ReplyReply Direct Link To This Post Posted: 18 March 2008 at 11:17pm
hi
i have the cct if this will help you
 
phoenix out of the ashes
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Monitech View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Monitech Quote  Post ReplyReply Direct Link To This Post Posted: 19 March 2008 at 11:26am
hi
hear is the info you need on the components
R41 = 4K7 / 0.6 W            R44 = 1K / 0.6 W
R48 = 3K3 / 0.6 W            R45 = 1K / 0.6 W
R43 = 22K / 0.6 W            R46 = 3K9 / 0.6 W
R61 = 3K3 / 3 W               R64 = 6K8 / 1 W 
R63 = 10K / 0.6W             R47 = 3K9 / 0.6W
R49 = 3K3 / 3W                R48 =100R / 0.6W
R68 = 3K3 / 3W       
Q11 = MPSA43                 Q13 = MPSA93
Q13 = 2N3340
ZD17 = 15V / 1W              ZD18 = 15V / 1W
D11 - 14 = 1N4148
C16/27 = 47uF 10V
C28/29 = 6u8 40V
VR 1 / 3 DC OFFSET adj
VR 2 / 4 BIAS adj
MEASURE THE VOLTAGE ACROSS R 18 /36 FOR BIAS
ITS BEEN ALONG TIME SO I CANT REMEMBER
IQ APROX =150MA
 
REGARDS
RICH
 
phoenix out of the ashes
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jbl_man View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 19 March 2008 at 3:30pm
One thing that strikes me looking at that photo,is how small the transformer is? i have a V800 here (basically the same amp,but with the led meters and handles) and the transformer is far larger,(at least half as big again) ,has someone changed the transformers?
Be seeing you.
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Akino View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Akino Quote  Post ReplyReply Direct Link To This Post Posted: 20 March 2008 at 10:17am
All 4 of them have the same type transformer,with the factory label HH156 badge still there.

I've never seen a V800 on the Inside.

Thnx for your information so far Monitech.
I will ad it soon to my HH M900 Service data file (14Mb,still working on it)
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EmPro View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote EmPro Quote  Post ReplyReply Direct Link To This Post Posted: 18 June 2022 at 12:27pm
i have 6 HH M900,just fit bigger stronger resistors on the back of the pcb and problem solved for 200+ years,as far i recall there are three of them that became hot as hell 3.3k,my amps have multiturn trimmers for bias and offset,same trasformer as my other HH V800 (+-75vcc)  and BHC filter caps,the V800 have LCR-s,after bias and offset adjustments,bigger resistors fited upside down in the ventilation airflow and full pcb resolderings my amps are bulletproof,for room loud listening the fan don't even turns on,the amps runs ice cold,and for outdoor events i have couple of them with bypassed thermal relay,so the fan is always on for maximum performance and stability. Wink

Edited by EmPro - 18 June 2022 at 1:01pm
EmPro Audio
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