AU-919: Peculiar behaviour of protector after recapping.

Helios

Active Member
I have just finished recapping my AU-919, replacing all electrolytics except the big oval ones. I have a strange behaviour when I put the main switch ON; I see the relays going to ON, then to OFF (protector mode) and ON again afterwards; needless to say that there is a scratch to the speakers when it is happening. If I wait a bit, then put the switch to OFF and then to ON, sometimes the ampli goes directly to the protector mode and then the relays are ON. When I inspected the pics that I took while doing the job, I observed that on the protector board (F-2840) the C03 and C04 were installed in reverse originally (see pics, before and after); on the schematic it is indicated for C03: 220 uF 6,3V (B.P.). I do not know what the BP stands for. Could it be the cause of this behaviour ? I must add too that on the Pre-Amp P/S board (F-2844), the C05 and C07 were originally installed in reverse; I installed the replacements like the SM and indications on the board told to do.

My second problem is what prompted me to do the recap process; I had lost the right channel. While recapping I inspected carefully the driver board (F-2839) and saw that one cap was doubful C38: 0,001 uF 100 V mylar (see pic). I tried hard to find replacements here locally but to no avail. I resorted to exchange the C38 with C37 just to make the test, and in fact now the right channel works while the left one is gone; so that must be the origin of the problem, no ? Can someone confirms that it might be possible, or do I have to look elsewhere ?



Helios
 

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I have just finished recapping my AU-919, replacing all electrolytics except the big oval ones. I have a strange behaviour when I put the main switch ON; I see the relays going to ON, then to OFF (protector mode) and ON again afterwards; needless to say that there is a scratch to the speakers when it is happening. If I wait a bit, then put the switch to OFF and then to ON, sometimes the ampli goes directly to the protector mode and then the relays are ON. When I inspected the pics that I took while doing the job, I observed that on the protector board (F-2840) the C03 and C04 were installed in reverse originally (see pics, before and after);

You should ALWAYS re-install caps the way they were installed at the factory - UNLESS you suspect another person has done work on the amp. In which case further investigation is needed. Treat the orientation information in the SM schematic and on the PCB with great caution - record ALL orientations as you take out the old caps - photos help with this.

on the schematic it is indicated for C03: 220 uF 6,3V (B.P.). I do not know what the BP stands for.

You should not be working on this amp if you do not know what that means !
It means 'Bipolar' - it would appear you have fitted Polar electrolytics here which may explain some of your problems.

Could it be the cause of this behaviour ? I must add too that on the Pre-Amp P/S board (F-2844), the C05 and C07 were originally installed in reverse; I installed the replacements like the SM and indications on the board told to do.

How were they installed originally? - see previous note !!!

My second problem is what prompted me to do the recap process; I had lost the right channel. While recapping I inspected carefully the driver board (F-2839) and saw that one cap was doubful C38: 0,001 uF 100 V mylar (see pic). I tried hard to find replacements here locally but to no avail. I resorted to exchange the C38 with C37 just to make the test, and in fact now the right channel works while the left one is gone; so that must be the origin of the problem, no ? Can someone confirms that it might be possible, or do I have to look elsewhere ?

Helios

Get 2 new caps and replace both - they are not hard to find, try Here
 
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Yes, the 6.3v 220uf are definitely BI-Polar and you need to order that kind. Also, both the 919's I restored had additional jumper wires with resistors and diodes soldered (by the factory) onto the trace side of the protection pcb. Did you remove anything like that on yours ?

Scott T.
 

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Yes, the 6.3v 220uf are definitely BI-Polar and you need to order that kind. Also, both the 919's I restored had additional jumper wires with resistors and diodes soldered (by the factory) onto the trace side of the protection pcb. Did you remove anything like that on yours ?

Scott T.

No Scott; mine is a late production unit. I have not some resistors and some black flags that I saw on yours. Only a few jumpers on the equalizer. I checked again for the caps that I had removed, and these are the only who are BP; I will reuse them.


Helios
 
no need to order enything, in my517 the bi polar cap i chenge them with polar just taking two of the same conect the two (-) and put the two(+) to the pcb.
 
Finally I made my order to Digikey to have this super rare (locally) 0,001 uF 100V; at the same time I ordered too Bourns 25 turns trimmers for the Driver Board, and 220 uF 6,3 V BP (P1144-ND) for the replacements of Elna CE-BP on the protector board. Now the two channels work properly, so the 0,001 uF was the cause of my problem.

I made the adjustments for the Equalizer and Driver boards (bias current, DC offset). The unit works just fine with all inputs: AUX, Tuner, Phono-1 and Phono-2. The Bourns trimmers were really welcomed, as the adjustments for the bias current are rather steep.


The problem with the protector that I had was due to the fact that one leg of the 470 uF (C606) was not properly soldered. Now it is working as it should.

Thanks again for the help, guys.



Helios
 
Hello...arrival a few years late: D C07 and C08
they are inverted with respect to the writing on the board F-2840
better late than never!!!;)
 
they are inverted with respect to the writing on the board F-2840

You mean F-2844 ? - F2840 does not have C07 & C08.

And for F-2844, and C07 & C08 only, they might be installed opposite to the PCB markings NOW - but that's how they should be, the amp has worked for 30 years like that.

There are some muddled up PCB and circuit references in Helios Posts above - beware!
 
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i never seen three-pin capacitors. I refer to the 1000uf ( c02/03) in board f 2844
where the third is for support only?!
 
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