CarAudioForum.com


Reply
Old 07-29-2003, 05:48 PM   #1
Seahag

Registered User
 
Join Date: Oct 2002
Location: Kitchener, ON
Posts: 622
Seahag is on a distinguished road



Amp repair

I have a Soundstream reference 1000s here that blew an 80 amp
fuse.
I took it apart and tested the transistors. All of them seem fine. No shorts.

what could be wrong?

Thanks in advance

Chris=========
Seahag is offline   Reply With Quote

Sponsored Links
Help Syrian Refugees Survive. Donate Now!
Or text REFUGEES to 50555 to give $10 to USA for UNHCR
Old 07-29-2003, 08:10 PM   #2
thylantyr

Registered User
 
Join Date: Jan 2002
Location: [Yoda] Belong to us all your base are...
Posts: 12,539
thylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond repute



It's possible to have bad transistors that are not shorted,
perhaps open-circuit. Sounds like you need to go
to the next level of amplifier repair.

Mosfet ?
Bipolar?

Do you read .7 using diode check on the bipolars?
base/emitter
base/collector

mosfet -> you can use the Nelson Pass mosfet checking
method..

Instead of using the meter to test for hardcore failures,
now maybe you need to actually place the transistors
in a circuit to see if it responds correctly.
http://www.passdiy.com/howto/matching.htm

Last -> After assembly of the amplifier with "good" parts,
instert a 5A - 20A fuse just to see if it comes up. Value
depends on the inrush current the amp draws -- which is
unknown.. that means you may blow a 5A fuse on a good
amp due to inrush ... so you might have to experiment.
I don't think a good amp would blow a 20A on turn on.
If the amp is still bad and you use too-high amperage
fuse -- you can blow the good transistors. Use your gut feeling
and wear the Jedi helmet... / lol
thylantyr is offline   Reply With Quote

Old 07-29-2003, 08:39 PM   #3
Seahag

Registered User
 
Join Date: Oct 2002
Location: Kitchener, ON
Posts: 622
Seahag is on a distinguished road



next step..

what would you do.. output.. then power supply?
or the otherway around.

Little story..

the guy i bought the amp off of had it sent out to soundstream to be fixed. they did a number of things.. and as i can see replaced 2 output transistors. (this apparently blew an 80 amp fuse)

He did not know where to get an 80 amp fuse.. so he put in a
50 amp. after it blew he got fed up and sold it.
he was running the amp at 1 ohm mono with 2 infinity perfects

could it be that the fuse is just wrong...

I DID not test this b4 i took it apart.. learn the hard way?

I`ll put it back together and check..
Seahag is offline   Reply With Quote

Old 07-29-2003, 09:03 PM   #4
thylantyr

Registered User
 
Join Date: Jan 2002
Location: [Yoda] Belong to us all your base are...
Posts: 12,539
thylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond repute



Always test first, never trust HuMans! /LOL

Prolly blew the 50A fuse because the amp
really drew that much power trying to drive 1 ohm.

/hehe
thylantyr is offline   Reply With Quote

Old 07-29-2003, 10:19 PM   #5
thylantyr

Registered User
 
Join Date: Jan 2002
Location: [Yoda] Belong to us all your base are...
Posts: 12,539
thylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond repute



Cliff on carsound posted this url.

not that you need it...

NPN and PNP check
http://www.kilowattclassroom.com/Archive/AN0007.pdf

diode check
http://www.kilowattclassroom.com/Archive/AN0001.pdf

Last edited by thylantyr; 07-29-2003 at 10:23 PM.
thylantyr is offline   Reply With Quote

Old 07-29-2003, 10:22 PM   #6
Seahag

Registered User
 
Join Date: Oct 2002
Location: Kitchener, ON
Posts: 622
Seahag is on a distinguished road



i tryed hooking it up to a 20 amp powersupply

nothing. theres no light on the amp indicating that its on.
I open it up and prob around.. theres power running
though it..

i hook up rcas.. nothing.. no sound..

the fuse doesnt blow.. but.. that might be because of the 20 apm powersupply..

what now?


I am starting to think i am huMan. hahaha
Seahag is offline   Reply With Quote

Old 07-29-2003, 10:24 PM   #7
Seahag

Registered User
 
Join Date: Oct 2002
Location: Kitchener, ON
Posts: 622
Seahag is on a distinguished road



ya know.. about the multi meter..

i got a diode check on my ohms setting.. thats it..

it doesnt measure volts..
i am getting reading like 450 on the "diode check" on the 2000 ohm setting.
Seahag is offline   Reply With Quote

Old 07-29-2003, 10:35 PM   #8
thylantyr

Registered User
 
Join Date: Jan 2002
Location: [Yoda] Belong to us all your base are...
Posts: 12,539
thylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond repute



Quote:
Originally posted by Seahag
i tryed hooking it up to a 20 amp powersupply

nothing. theres no light on the amp indicating that its on.
I open it up and prob around.. theres power running
though it..

i hook up rcas.. nothing.. no sound..

the fuse doesnt blow.. but.. that might be because of the 20 apm powersupply..

what now?


I am starting to think i am huMan. hahaha
doh..

If the bench PS holds 12v and doesn't drop voltage when trying to
turn the amplifier on, then the ps is ok to power the amp. If
the power supply is weak as soon as you connect the
amplifier turn on wire, the voltage coming out of the PS
will sag down alot.... this is a sign of a weak supply...

I use a cheap old car battery... /heh

See if you can measure rail voltage - but you said the power
light is not on...

If you are sure the transistors are good, then the circuits
that turn on the switcher could be toast. I've only seen
this once in amp repair.. I would trace the turn on wire
on the pcb to find out where it goes -- other small signal
transistors? chips? diodes and check from there.

If... big if .... the power supply transistors are ALL
open circuit, then I can see this problem occuring, but
that is so rare that all transistors would open-circuit.

What about the output stage? is there a shorted transistor
that would cause the amplifier *not* to turn on because
it's built-in protection circuit is preventing it from turning on?
I don't know the details on that amp, does it have output
short circuit protection?

If all else fails and you tried everything, maybe remove the
output stage transistors -- to verify that there is no funny
business going on -- hoping the DC-DC power supply will
turn on... See if you can meausure the rails, typcally you
can use the meter and measure across the output power
supply caps, the ones next to the power supply with
higher voltage ratings... in pairs, one for +v, one for -v.

Do you have a spare diode ? any diode? -- to check
your meter for proper functionality.....The diode
check on your meter should read .6 (give or take .1),
should not read 450 ....

Last edited by thylantyr; 07-29-2003 at 10:38 PM.
thylantyr is offline   Reply With Quote

Old 07-30-2003, 03:13 PM   #9
Seahag

Registered User
 
Join Date: Oct 2002
Location: Kitchener, ON
Posts: 622
Seahag is on a distinguished road



I cant seem to measure the rail voltages. I dont know there to probe.

My multi meter looks like this.
http://www.avalonrise.com/catalog/im...eter_519_b.jpg

I need to set to ohms 2000 in order to get the diode check..
http://www3.sympatico.ca/chris.haig/Multimeter.JPG





For some reason if I loosened up the bolts that hold the transistors in,
the High power light came on
(The transistors are clamped to he top of the heatsink between the board.)

I don`t know why is it called high power?
dunno? I think its the power light


When I try hooking up a speaker.. I get sound!
I tried the other channel and POOF.. the power goes out in my apart.
Apparently the whole apartment is on 1 circut. I had the toaster, microwave ,
tonnes of lights, computer tv, stereo....
all that on a 15 amp circut.
I dunno if it was a coincidence? but I am scared to try again.

As far as the Clamping and it, and it turning on...
I moved the board around and then tried reclamping it. the light goes out on 2 of the bolts... if I loosen them off slightly, the light comes back on.

I measured the middle pin of power supply transistors to the heat sink and i am getting an open circut.

as well.. when I measure the ohms on the other 2 bolt locations and when I tighten them down I get a open circut between the middle pin and the heat sink..

I looked at the sheet (mica stuff) it looks Fine? theres no indication of wear.

Is this normal.. ?

Last edited by Seahag; 07-30-2003 at 03:17 PM.
Seahag is offline   Reply With Quote

Old 07-30-2003, 04:12 PM   #10
thylantyr

Registered User
 
Join Date: Jan 2002
Location: [Yoda] Belong to us all your base are...
Posts: 12,539
thylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond repute



I cant seem to measure the rail voltages. I dont know there to probe.

You won't measure anything if the amp doesn't turn on.
Locating the rail voltages - another way is to identify
the output ground from the DC-DC power supply.
(Not the input power ground). Practice makes perfect.
Then use this ground reference and probe with the red meter
lead on the transistor pins until you read +v, then the other
set of transistors (maybe located on the opposite side of
the board) will read -v.

Your meter is fine, just get a brand new cheap diode
and make sure the diode check works correctly - to verify.

For some reason if I loosened up the bolts that hold the
transistors in, the High power light came on (The transistors are
clamped to he top of the heatsink between the board.)


The transistor metal tab on the back needs to be electrically
isolated from the heatsink.. because the tab on transistors
is actually connected to one of the three transistors pins
and if it's not isolated, you are shorting that pin to the heatsink
which is connected to ground (maybe) or the complementary
transistor pins.. The mica insulators are typically used with
silicon heat compound --> to help transfer heat from the
transistor to heatsink.. You may also see the grey pads
that don't need the white goo. Use the DMM on "ohms"
and measure each transistor tab to heatsink and it should
not read "short" or low resistance -- should be open.
But, heatsinks are anodized which doesn't conduct electricity
so when you touch the meter probe on the heatsink, try
to find a bare spot or insert the meter probe into a threaded
hole on the heatsink to ensure you are making electrical contact.

You can do this before/after you tighten the bolts -- to see
if something happens. Also, make sure there is no wires leads
sticking out under the pcb that may touch the heatsink when
you re-assemble the amp.

post pic.
thylantyr is offline   Reply With Quote

Old 07-30-2003, 04:29 PM   #11
Seahag

Registered User
 
Join Date: Oct 2002
Location: Kitchener, ON
Posts: 622
Seahag is on a distinguished road



The amp does turn on when the selected screws arent tightened down.

I looked and there doesnt seem to be damage to the mica.
I dont understand when i tighten the bolts down there is a short.

does this mica stuff breakdown?

should i replace it?

if i move the board around , different screws are the culprit.



I cant post pics at the moment.. if i dont get this sorted out soon i will take good pics.
Seahag is offline   Reply With Quote

Old 07-30-2003, 04:42 PM   #12
thylantyr

Registered User
 
Join Date: Jan 2002
Location: [Yoda] Belong to us all your base are...
Posts: 12,539
thylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond repute



Screw problems ?

You probably are creating a short somewhere when
clamping.. after you clamp, use the meter to check for
shorts.. there is a gremlin somewhere hiding..

A new meaning to the word ..... / being screwed /



/hehe
thylantyr is offline   Reply With Quote

Old 07-30-2003, 05:19 PM   #13
TO-3

Registered User
 
Join Date: Jul 2000
Location: Scottsdale
Posts: 1,034
TO-3 is on a distinguished road



Quote:
Originally posted by Seahag
The amp does turn on when the selected screws arent tightened down.

I looked and there doesnt seem to be damage to the mica.
I dont understand when i tighten the bolts down there is a short.

does this mica stuff breakdown?

should i replace it?

if i move the board around , different screws are the culprit.



I cant post pics at the moment.. if i dont get this sorted out soon i will take good pics.
If the amp runs without screws, I am assuming the lid has fingers on it to apply pressure on the xistors to press to the heatsink, turn the amp on without the lid. Then press down on each of the metal tabs on the TO-220s. When you push on a tab and the power cuts out, lift that device and scrape the sh!t out from under it, "spooge" it and you should be good to go.
Jon

Last edited by TO-3; 07-30-2003 at 05:23 PM.
TO-3 is offline   Reply With Quote

Old 07-30-2003, 05:28 PM   #14
Seahag

Registered User
 
Join Date: Oct 2002
Location: Kitchener, ON
Posts: 622
Seahag is on a distinguished road



THE TRANSISTORS ARE LAID AGAINST THE BOARD AND SANDWITCHED BETWEEN THE BOARD AND THE HEAT SINK.
This makes it hard to test if the tabs are shorting.. i just measured the middle pin..




I just whipped off all the grease
and cleand the sink and mica.

The mica stuff is pitted but not shorted out.

I will replace it and see what happenes.

what kinda grease am i looking for?

Thanks

Last edited by Seahag; 07-30-2003 at 05:36 PM.
Seahag is offline   Reply With Quote

Old 07-30-2003, 05:36 PM   #15
thylantyr

Registered User
 
Join Date: Jan 2002
Location: [Yoda] Belong to us all your base are...
Posts: 12,539
thylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond reputethylantyr has a reputation beyond repute



thermal heatsink compound

same shiznit used for computer CPU installs...

radio shack has the white goo..

i just measured the middle pin..

cool.... this pin connects to the tab right /just checking..



//// another note //////

Is the screws going thru the transistor hole? or
is the screw just part of the clamp assembly
and doesn't go thru the transistor hole.

Last edited by thylantyr; 07-30-2003 at 05:39 PM.
thylantyr is offline   Reply With Quote

Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT. The time now is 07:24 PM.
Powered by vBulletin® - Copyright © 2000 - 2014, Jelsoft Enterprises Ltd.
Copyright 1996 - 2011 by CarAudioForum.com - all rights reserved.