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1979 sanyo receiver blowing fuses

Zenbrewer

Nov 9, 2014
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OK thanks
first thing we need to prove is if that large bridge rectifier is the cause
That's the large black block immediately to the right of the yellow wires in pic's 1&2

how do i go about testing it?
 

davenn

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the second thing i noticed is what appears to be something missing in the board #2
which lead me to look at the amp pictures where i saw #3
the final thing is that what i think is a small heat sink is melting the board a bit #4

#2 & #3 ... doesn't look like anything has ever been soldered there
#4 ... may be a worry .... we look at that after the other main hassle
same with the diode

OK

cct2.JPG


See if you can identify those 2 wires I have highlighted blue that go from the power board to the main amp board
They will be the higher voltage supplies to those power modules
you can see each connects 3 in from the end on the amplifier board
disconnecting them and powering on again will prove if that big rectifier is causing the fuse to blow

Dave
 

Zenbrewer

Nov 9, 2014
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#2 & #3 ... doesn't look like anything has ever been soldered there
#4 ... may be a worry .... we look at that after the other main hassle
same with the diode

OK

View attachment 17042


See if you can identify those 2 wires I have highlighted blue that go from the power board to the main amp board
They will be the higher voltage supplies to those power modules
you can see each connects 3 in from the end on the amplifier board
disconnecting them and powering on again will prove if that big rectifier is causing the fuse to blow

Dave
Diconnected amp power as mentioned and fuse blew.
Should i now start digging online to find a rectifier?
Any ideas where to buy one?
 

davenn

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get back to you soon with that
am busy at monday morning work at the moment :)
 

Zenbrewer

Nov 9, 2014
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So digging a little I found an exact replacement for the bridge rectifier, at it seems a bit pricey. I also found multiple bridge rectifiers on other sites for much much less. The part number is s5188, and one website notes it as a 200v 11a. Would any 200v 11a rectifier work in its place? Or will the mounts be different? .
Is it possible to remove and repare the bridge rectifier?
 

davenn

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sorry about the late reply, been a hectic few days

what do you call a bit pricey ? should be $10 or less + shipping

no you cannot repair it, the diodes are all encapsulated

the KBPC1504G is an ideal replacement 15A 400V but seem to be currently in short supply from a lot of the suppliers

Mouser have them in stock for several prices up to $3.97
http://au.mouser.com/Search/Refine.aspx?Keyword=KBPC1504

Yes anything from 200-400V and 11 - 15A should do, just make sure it has wire leads and not tags

Dave
 
Last edited:

davenn

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That should keep you out of trouble :)

EDIT ... Oh and after you remove the old one BUT BEFORE you install the new one
check and see if the fuse blows
 

Zenbrewer

Nov 9, 2014
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Pulled the bridge rectifier and powered up.
Pretty lights but no blown fuse.
Just waiting for the mailman now
 

Zenbrewer

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That should keep you out of trouble :)

EDIT ... Oh and after you remove the old one BUT BEFORE you install the new one
check and see if the fuse blows
Well sadly
Without the bridge in place the fuse did not blow.
With the new bridge rectifier in place it blew.:eek:
I still have not reinstalled the high voltage leads to the amp or replaced the two large power supplys.
Should these need to go back in?
Or is there another possibility?
 

Zenbrewer

Nov 9, 2014
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Should i look at that extra large capacitor listed on the diagram as c910?
Seems like its the next thing in line after the bridge rectifier.
I am getting the concept that i could isolate things further by removing one or more parts from the circut past the rectifer to tell me what it could be.but couldnt i also use the voltmeter to run tests on diodes, capcitors, etc?
 

davenn

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greetings

was just having another hard look over that diagram and realised I didn't pick up on something the other day
that's the problem when am at work but doing internet hahaha

here is an updated pic with a few extra colours.....

cct3.JPG


OK
sorry that this was overlooked earlier ....
This main supply from that bridge rectifier is a split rail supply. That is there is a + V, a 0V and a -V rail

When I got you to disconnect the blue leads, you were only disconnecting the + rails to each of the 2 amplifier output stages

So, lets take a step back and sort out one amp module at a time
we may still find that one or both or neither are faulty .... hope you have a good stock of fuses ;)

so this time, with the new bridge rectifier in circuit, disconnect the blue and yellow wires say from the lower diagram connections. Power up and see if fuse blows, if so, disconnect the top blue and yellow and try again
if it does THEN NOW that will definitely prove the fault to the PSU board.

lets try that and then ponder next step :)

Dave
 

davenn

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Should i look at that extra large capacitor listed on the diagram as c910?


C910 and C911 are the 2 smoothing caps off that bridge rectifier ... 910 for the + rail, 911 for the - rail.

how do they look to a close inspection ? any sign of bulging or heat stress ?

if so replace. if not they may be OK but if the system is over 10 - 15 yrs old and had a lot of use, they may be drying out anyway and replacing wouldn't hurt in the long run

They are not likely to be the reason for the blowing fuse


D
 

Zenbrewer

Nov 9, 2014
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greetings

was just having another hard look over that diagram and realised I didn't pick up on something the other day
that's the problem when am at work but doing internet hahaha

here is an updated pic with a few extra colours.....

View attachment 17190


OK
sorry that this was overlooked earlier ....
This main supply from that bridge rectifier is a split rail supply. That is there is a + V, a 0V and a -V rail

When I got you to disconnect the blue leads, you were only disconnecting the + rails to each of the 2 amplifier output stages

So, lets take a step back and sort out one amp module at a time
we may still find that one or both or neither are faulty .... hope you have a good stock of fuses ;)

so this time, with the new bridge rectifier in circuit, disconnect the blue and yellow wires say from the lower diagram connections. Power up and see if fuse blows, if so, disconnect the top blue and yellow and try again
if it does THEN NOW that will definitely prove the fault to the PSU board.

lets try that and then ponder next step :)

Dave

Dont mind the overlook becuase id be nowhere at all without the help;)

Connected the +v and -v rail to the left side of amp only, fuse blew.
Disconnected the left side +v and -v rail as well and fuse blew.

Looks like it is a psu problem
You mentioned it was not likely the smoothing caps.
So the other things noticed crossing into the voltage rails are the following resistors.
R901,902,911,912
My rookie side of course wouldnt know what to do with them. Just learning to read:)
Let me know what you think would be the next logical step.
 

duke37

Jan 9, 2011
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Put a light bulb in series with the mains input, then you will not blow a 4A fuse..

Measure the voltages at the output of the bridge and further down the line. If there is a dead short you will get no voltage but if there is a partial short you should find if it is the + or - supply which is faulty.

Check the old bridge with a meter.
 

davenn

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Connected the +v and -v rail to the left side of amp only, fuse blew.
Disconnected the left side +v and -v rail as well and fuse blew.

what about the right side ? you didn't comment

disconnect the yellow and blue's from left and right sides
 

davenn

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OK to confirm, so with the 2 sets of yellows and blues disconnected, the fuse still blew ?

Ohhh to stop fuses blowing during testing note what duke37 said a couple of posts back .... the old trick is to put a 100W 120V light globe in series with the mains live wire to the unit under test ... if you have a globe holder around and a power plug and socket and suitable 120V cable to make it up.

If fuse still blowing with all 4 wires disconnected 2 x yl and 2 x bl. then yes fault is elsewhere in PSU board

check 4 caps around bridge rectifier C901 to 904. those may be disc ceramics ? maybe 0.01uf or 0.1 uF

Check R's 901 and 902 they are across the supply rails and discharge the C910, 911 caps when the power is turned off, they should be highish values
maybe ~ 10k Ohms

there's also a + rail that meanders out to the right to R952 that feeds the relay. other than that I don't see any other feeds off either of the rails

have labelled the 3 resistors and 2 large caps to check


Dave
 

Zenbrewer

Nov 9, 2014
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OK to confirm, so with the 2 sets of yellows and blues disconnected, the fuse still blew ?

Ohhh to stop fuses blowing during testing note what duke37 said a couple of posts back .... the old trick is to put a 100W 120V light globe in series with the mains live wire to the unit under test ... if you have a globe holder around and a power plug and socket and suitable 120V cable to make it up.

If fuse still blowing with all 4 wires disconnected 2 x yl and 2 x bl. then yes fault is elsewhere in PSU board

check 4 caps around bridge rectifier C901 to 904. those may be disc ceramics ? maybe 0.01uf or 0.1 uF

Check R's 901 and 902 they are across the supply rails and discharge the C910, 911 caps when the power is turned off, they should be highish values
maybe ~ 10k Ohms

there's also a + rail that meanders out to the right to R952 that feeds the relay. other than that I don't see any other feeds off either of the rails

have labelled the 3 resistors and 2 large caps to check


Dave
Do not have the right meter to read in uF but digging a little found the idea of testing capacitors using the ohms setting.
Did this to C901, 902, 903, 904
903 and 904 slowly ran up to 2k and in the reverse direction slowly went from -1k to 0 back up to 2k.
C901 to 902 however read .001 bolth directions.
From what i read this was showing me that 901 and 902 were short.
Removed them from the board and they read nothing at all.

Am i on the right track with this?
Or do i need to buy a new meter?

Is there any way to read the resistors using this meter?
 
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