au-717 not happy

U

Underworld

New Member
I have an au-717 that is not working. Initial troubleshooting:

1) all fuses test good
2) no bias voltage on either channel (no change with adjustment either)
3) test on each channel for voltage on 12 to 3 shows erratic voltages... 380ish volts, then 70ish volts, then 0... it doesn’t stabilize. 12 to ground shows same.
4) test on power board for voltage at 21 to 23 and 22 to 24 shows same erratic voltages... 380ish volts, then 70ish volts, then 0.

This all makes me think the power board is bad... not sure what to treat next to narrow down the issue.

any help is much appreciated!
 
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Underworld said:
I have an au-717 that is not working. Initial troubleshooting:

1) all fuses test good
2) no bias voltage on either channel (no change with adjustment either)
3) test on each channel for voltage on 12 to 3 shows erratic voltages... 380ish volts, then 70ish volts, then 0... it doesn’t stabilize. 12 to ground shows same.
4) test on power board for voltage at 21 to 23 and 22 to 24 shows same erratic voltages... 380ish volts, then 70ish volts, then 0.

This all makes me think the power board is bad... not sure what to treat next to narrow down the issue.

any help is much appreciated!
Click to expand...

also, forgot to mention that it does come out of protection mode, and i can hear the relay switch.
 
Assuming 380mv?

Has this 717 ever been service or more importantly has the glue been removed on the power and two driver boards?

Among many issues that are problematic with the 717 (fusistors, dual diodes) the glue is corrosive and has.most likely decayed one or more components it has touched.

With mine I could not see the damage until I removed the power board. Here is an example:

20200208_094524.jpg
 
MIJ_Pioneer said:
Assuming 380mv?

Has this 717 ever been service or more importantly has the glue been removed on the power and two driver boards?

Among many issues that are problematic with the 717 (fusistors, dual diodes) the glue is corrosive and has.most likely decayed one or more components it has touched.

With mine I could not see the damage until I removed the power board. Here is an example:

View attachment 1788775
Click to expand...

I haven't checked that yet...

I'll be pulling the board out later to check it. If that is the issue, can I just clean up the glue? Or is it likely that some components are fried?
 
All the 717s are full of garbage at this point. All of the glue has to come off. Everything the glue touched should be replaced. This will include diodes, resistors, and capacitors. All of the fuse resistors need to be replaced. There are capacitors, transistors, and diodes that should be replaced as part of a restoration, but are not necessarily failure points right now.

Ideally what you would be doing with any AU-717 (or other amp in the series) is replacing every electrolytic capacitor, every small transistor, every fuse resistor, every blob diode, and everything that was touched by the glue.

I rebuilt one of these. It was not a whole lot of fun. I replaced everything except the main capacitors, which tested good and I didn’t feel like doing. Removing the glue is agonizingly slow and involves acetone and cotton balls.
 
EastPoint is right. I went the route of doing a full overhaul and replacing all diodes/transistors/electrolytic capacitors, and a few others. I found it difficult to work on, removing that glue really is irritating. However it's very rewarding when it is complete.

Here is some info that will help:

https://audiokarma.org/forums/index.php?threads/au-717-recap.903438/

Underworld said:
I haven't checked that yet...

I'll be pulling the board out later to check it. If that is the issue, can I just clean up the glue? Or is it likely that some components are fried?
Click to expand...

Pulling the board out requires documenting what goes where and desoldering about 10 or so wires. Make sure you are committed when you start. Have you done this kind of work before? Do you have a dim bulb tester?
 
Thanks for the info...
I did have a meter issue... it’s auto ranging, and i thought auto sensing ac/dc... both of which caused the erratic readings.

am now getting more appropriate readings based on what I’ve read elsewhere on the forum...

Will be pulling the power board still to check it over... likely will have more questions in the coming days.
 
MIJ_Pioneer said:
Assuming 380mv?

Has this 717 ever been service or more importantly has the glue been removed on the power and two driver boards?

Among many issues that are problematic with the 717 (fusistors, dual diodes) the glue is corrosive and has.most likely decayed one or more components it has touched.

With mine I could not see the damage until I removed the power board. Here is an example:

View attachment 1788775
Click to expand...

Wow that glue is some nasty $hit! Had no idea it would rot stuff away like that. It’s like a disease.
 
playittwice said:
Wow that glue is some nasty $hit! Had no idea it would rot stuff away like that. It’s like a disease.
Click to expand...

Yeah I was surprised when I first saw it too. The 717 I had was still working with very low miles on it. Shame too because it's not an easy fix for a non enthusiast.
 
The power board can be pulled out the bottom along with all the filter caps and no wires unsoldered. Recap it (it’s out so now is the time) remove glue (I scrape and pick it off, no need to be perfect, just get it off the components) replace anything that corroded became of the glue.

The amps are out to get the power board and caps out, recap them and replace all fusistors with metal film resistors.

Pull the pre-amp/function board, replace fusistors and recap while there.

As long as it’s apart, finish the recap. Last boards behind face.

Reassemble and test. Adjust as needed or trouble shoot now that known issues are fixed.

The only transistors that may be an issue are some trouble makers that get noisy in the Phono section. All others, as long as they are not actually blown, are fine.

I’ve rebuilt 6-7-8 (?) of these and only found noisy phono transistors in one. I’ve never had to replace any transistors to “fix” them.
 
1. The amp will probably sound better with transistor replacement--less background noise.
2. I'd rather have the amp completely done now, than have a transistor go bad six months after it's rebuilt.
3. Transistors are really cheap. If you're buying in bulk, you can redo all the small transistors in an AU-717 for maybe 2-3 bucks.
4. I'd rather shotgun them now than have to pin down which one is acting up if one does go bad.
5. Half the labor on this is removing the glue and getting access to the boards. As long as you're in there, why not do the transistors?
6. If you're quick and have a nice desoldering gun, you can redo a transistor in 30 seconds or a minute, so clearing them out shouldn't add much time.

I get why other people don't do it, and I don't want to start an argument, but these are my reasons.
 
The AU-717 contains few if any transistors that are difficult to find replacements for, so recommending wholesale replacement might seem like a good idea, providing the correct replacement types are used. However because of the quite severe glue damage seen in these models, cleaning the glue, and replacing many glue damaged components is also required along with the usual other activities and capacitor changes. And then adding on changing all the small signal transistors I feel for some, can be a bit too much, substitute transistor pitfalls can easily catch out the unwary for one reason or another.

Unfortunately people extend the transistor replacement idea into other areas, and to models which are unsuited to this approach, believing incorrectly, that the newer so called replacements are better, when they are not. Last but not least, the replacement of standard diodes and rectifiers - this is plain ridiculous - there is seldom a need to do this.

Finally, when I reconditioned my AU-717 (which I have owned from new), I changed one transistor, the relay driver transistor - and only because EW said it would be tired. I have never had any transistor failures of any kind, including the badly behaved ones. YMMV.
 
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Hyperion said:
. Last but not least, the replacement of standard diodes and rectifiers - this is plain ridiculous - there is seldom a need to do this.
Click to expand...

Ehhhhhhhhh, it really depends what model you're talking about. I have seen a number of 5050s and 6060s with shorted power supply diodes, and I replace those on sight. Redoing all ten zillion little glass diodes on an AU-717? Probably not necessary, but anything the glue touched should be replaced, IMO.
 
Hyperion said:
Well, obviously failed diodes or rectifiers should be replaced, but I am talking about NOT replacing diodes and rectifiers 'just because they are old'. :)
Click to expand...

What I'm saying is that I pre-emptively replace them in some gear, just on the expectation that they will fail sooner or later.
 
EastPoint said:
What I'm saying is that I pre-emptively replace them in some gear, just on the expectation that they will fail sooner or later.
Click to expand...
My personal view is that this is a false expectation, except for example in some (exceptional), cases where an upgrade demands a more robust part to be installed. ;)

I sometimes change parts that are not faulty, to replace them with an upgraded part, with advantageously better performance. But what I see are people routinely replacing 1S2493 diodes with 1N4148's - there is no advantage in doing that, and no indication that a 1S2493 'will fail sooner or later'

Apologies to the OP whose thread is a bit messed up now.
 
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Goodaye all

On my 717 l had a lot of mismatching parts on both channels or the power and driver boards so l changed them all to matching.
l also had a fault l was chasing.

Hoping not to much more than a recap on the other boards.

l feel its a good idea to have matching parts on both channels.

regards Bruce
 
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