Pioneer SX-950 faults at 125 Volts in Owners house

[Palmer]

I have a client who had me go over his Pioneer SX-950, he had it done- quite thoroughly, by a service tech prior - he told me it cuts out, randomly. Not volume related. Comes back after 20 seconds or so. Opened the unit up, the original tech did not change the relay in the power amp side - I got a new relay, better than the original. Tested everything, DC bias fine, Rail voltage fine. Ran the amp in my place for about 2 days straight, 2 speakers, 4 speakers - no issues. Client picks it up, brings it home. Fine for about 2 days - guess what, cuts out. So I go to the clients house - and just out of curiosity I measure his outlets. 124.8 to 125.0 Volts. That's exactly where about these older receivers run into issues, especially with the fault circuit.

As I find out, the Service providers don't spring into action unless it's above or at 126 Volt. Neither will the HOA. So there's that. Now, I disconnected the Pre- from the Power-, and loaned him a Fosi Audio V3, and that works just fine. However the client wants to modify the Receiver, so it's perfectly capable to run in his house - on the AC he gets. I suggested other options - but that's what he wants.

So if anybody has re-worked an older Receivers Power supply for issues like that - I would really appreciate any input.

Cheers and thanks

 

[mhardy6647]

Addition of a bucking transformer isn't a terribly elegant solution but solves the problem with a minimum of hardware & effort.
"We" do it with seriously old vacuum tube hifi all of the time. It's easier than adjusting components in the circuit and/or in the P/S to accommodate higher mains voltage.

Bucking Xfmrs

Bucking Transformers - What they do, how they do it, and how to determine the proper transformer to use

sound-au.com

 

[Palmer]

Addition of a bucking transformer isn't a terribly elegant solution but solves the problem with a minimum of hardware & effort.
We do it with seriously old vacuum tube hifi all of the time. It's easier than adjusting components in the circuit and/or in the P/S to accommodate higher mains voltage.

I wholeheartedly agree - that's what I suggested. However - this particular gentleman wants it inside of the amp. That would be difficult. Not that much room in there...

 

[mhardy6647]

I wholeheartedly agree - that's what I suggested. However - this particular gentleman wants it inside of the amp. That would be difficult. Not that much room in there...

Much easier to fix with an outboard solution!

 

[Devnull]

Have the primary power transformer rewound with fewer output turns.

 

[Palmer]

Tell me about it. I rarely do anything in the amp/ preamp department, turntables are my passion. But this fellow came through a connection, and I had to help out. No good deed goes unpunished...

Cheers

 

[kyuu]

It's unsurprising no one will do anything about the voltage hanging about at 125VAC, since that's in-spec. AVRs typically don't buck the voltage until it gets over 127V, and of course one of those isn't going to fit in the case anyway.

Unless you're going to replace the power supply with a modern design that doesn't choke on normal voltage deviation, the only easy solution would be something like a double-conversion online UPS which of course is an external device.

 

[Hayabusa]

I have a client who had me go over his Pioneer SX-950, he had it done- quite thoroughly, by a service tech prior - he told me it cuts out, randomly. Not volume related. Comes back after 20 seconds or so. Opened the unit up, the original tech did not change the relay in the power amp side - I got a new relay, better than the original. Tested everything, DC bias fine, Rail voltage fine. Ran the amp in my place for about 2 days straight, 2 speakers, 4 speakers - no issues. Client picks it up, brings it home. Fine for about 2 days - guess what, cuts out. So I go to the clients house - and just out of curiosity I measure his outlets. 124.8 to 125.0 Volts. That's exactly where about these older receivers run into issues, especially with the fault circuit.

As I find out, the Service providers don't spring into action unless it's above or at 126 Volt. Neither will the HOA. So there's that. Now, I disconnected the Pre- from the Power-, and loaned him a Fosi Audio V3, and that works just fine. However the client wants to modify the Receiver, so it's perfectly capable to run in his house - on the AC he gets. I suggested other options - but that's what he wants.

So if anybody has re-worked an older Receivers Power supply for issues like that - I would really appreciate any input.

Cheers and thanks

Insert a few serie/parallel diodes in mains path?. Each pair would reduce by 0.7 v

 

[kyuu]

Not an electronics expert, but isn't putting diodes into an AC circuit making a rectifier?

 

[Redacted]

We've all been in a situation where, after analysis, you present solution A or solution B. The user wants the solution C, as A and B are not acceptable to him. You explain what solution C involves, and user doesn't fancy it either. In this situation, I'd politely explain I can't help, and walk away. Experience has shown me that avoiding misery for all is the best way to stay on good terms.

 

[Hayabusa]

Not an electronics expert, but isn't putting diodes into an AC circuit making a rectifier?

two in anti parallel:

 

[Palmer]

Insert a few serie/parallel diodes in mains path?. Each pair would reduce by 0.7 v

Did not think of that, I am admittedly a little rusty... Appreciate it.