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Is your unobtainium power switch worth $5 and an hour or so of your time?

Matkot said:
Hey,

while I am currently working on cleaning the power switch with a Q-Tip, I also prepared two schematics for discussion:

1. The Original Wiring Schematic of my Pioneer SX 750:
View media item 18850
2. The TRIAC Wiring Schematic:
View media item 18858

Am I on the right path?
Click to expand...

Hey there,

I tried this on my own 750 but after power on the transformer starts humming like crazy (not on the dim bulb btw).
Is there another iteration of your schema or am I doing something very, very wrong?

Bert
 
Ah, and now the entire sx-750 is dead. So either the transformer died on me or the triac is busted.
I hope it is the triac :-(. Not sure why it failed as that schematic was implemented and looks fine.
So let's remove the entire setup, see if the old method powers the machine and implement a secondary bypass power switch.
Too bad, this looked like a nice method to prevent butchering the machine.
 
The European units usually have a double pole switch, and switch both side of the AC line input. The US and Canadian modes have a single pole switch, so it is easy to replace the switch with a single triac. I have thought a lot about the difference, but have never come up with a way that works correctly, protects the switch, and still meets the European legal requirement of switching both sides using a triac. It is easy using a double pole relay that has a 220/240vac 50Hz coil.
 
merlynski said:
The European units usually have a double pole switch, and switch both side of the AC line input. The US and Canadian modes have a single pole switch, so it is easy to replace the switch with a single triac. I have thought a lot about the difference, but have never come up with a way that works correctly, protects the switch, and still meets the European legal requirement of switching both sides using a triac. It is easy using a double pole relay that has a 220/240vac 50Hz coil.
Click to expand...

This unit uses a three pole power inlet, it is more like US models. So the live and neutral (and groiud) are always the same and the power inlet even has that intel printed on the back.
So basically in this scenario is should be possible to implement that triac in the 'US method'.

I used a Littlefuse triac which was way overspecced but something must have gone seriously wrong. I doublechecked my implementation and it is as the schema 'dictates'. Out of frustration I didn't look at the machine yet to see what has failed. I am crossing my fingers it is not the transformer.
 
For the implementation it is electrically irrelevant which leg the triac is on, neutral or live.
Unless you left it on for a long time and over-heated the transformer, the transformer is probably OK. What usually happens when a transformer overheats, is an internal thermal fuse opens, rendering the primary winding side an open circuit. Test the primary winding with an ohmmeter. it should be just a few ohms.
I believe the reason for the double pole power switch is government / safety regulations. There is no electrical reason to need a double pole switch.
If you can implement it without breaking a law you can use a triac on just one leg of the AC line.
The drawings you provided are not done with normal electronics symbols, which makes them VERY difficult to interpret.
Are you using it in a location with 220/240vac 50Hz AC mains?
 
A single pole power switch depends on the polarized plug and that the house power outlet is wired correctly to insure the switch is in the hot wire on 110v system.
Many 1950 and before radios did not have polarized plugs and it was 50/50 that the power switch is in the hot wire. I have a Hallicrafters S-77A SW receiver that had a hot metal case with the plug in one way and the power switch ON and with the plug in the other way, it had a hot metal case with the power switch OFF! This tube radio has all the tube heaters wired in series giving a required 110 vac load.
I took the wire and polarized ALCI (Appliance Leakage Current Interrupter) power plug from the hair dryer and installed it on the S-77A receiver to make it safe to use.
Charlie
 
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Damn I totally forgot about the double pole switch, it's not legal then (or you must double the triacs).
Let me check this tomorrow, I'm not in the lab at the moment.
This machine is indeed on 230Vac with a 50hz mains, it's in Europe.
These old transformers are unlikely to have a thermal fuse.

That image is not a schematic, more like a visualisation of wires.
It was implemented on an EU machine, so seemed safe. But again, no considerations were made for the switch.
Let's see what I can find tomorrow (if I have the time).
 
Just performed this mod on my MAC1500 and it works very well, no hum and no issues so far. I heard about the MAC’s power switch issues and how unobtainable they are and decided to take the plunge and do it. Took longer to read about how to do it properly than to actually do it properly. 9A91D925-7D0D-4254-9F86-61BA04DAB7EA.jpeg
 
1rebmem said:
Matkot......I opened up my 750 to get you some pictures. Hopefully this works for you.

Hand sketch of how I wired mine. I made notes of wire colors as they are in mine. I don't think I used any new wire but was able to re-route the 750's wires.
View attachment 1510455

Overall shot. I mounted the triac along side of the power transformer. I drilled one hole and secured the triac to the sheet metal using a sheet metal screw. The triac has some thermal grease smeared on it to transfer heat to the sheet metal.
View attachment 1510465

As you know, the power switch is the brownish bakelite cover with the 2 terminals. Originally there is a capacitor soldered across the 2 terminals, clip that cap out and chuck it, not needed. One terminal now has the 100 ohm resistor soldered to it. The other end of the resistor attaches to a new solder terminal strip which again, I drilled one hole and to attach said terminal strip. So after the mod is done, one switch terminal has a resistor attached and the other has one wire which goes to the triac.
View attachment 1510476

Next shot shows the wiring on the underside of the convenience outlets. You can match up wire colors on the hand sketch.
View attachment 1510480

And the triac and fuse. Compare your original wiring on the fuse. Now the right side of the fuse has 2 wires attached. The new wire (yellow) goes to the power switch.
View attachment 1510491

Let me know if this doesn't fully show what you need.

Edit: I just remembered, I didn't rewire the unit so that ac power inlet hot wire goes first to the fuse then to the unswitched outlet. That would be the most correct way BUT to ensure the ac hot always went to the fuse you'd have to put a polarized power cord on it.
Jef
Click to expand...
Thanks SO MUCH for these entries. Fixing up my daughters SX-750 based on this, with a Littlefuse Q4025L6TP from Arrow Electronics. Due next week. Do I have a 100 ohm resistor for the gate resistor in the basement? Time will tell. I'll also print a sticker on the xfrmr... good form.
 
Would a Bryston B4 power amp be a candidate for this mod?
I did the mod on my Sanyo Plus 55 receiver and I have a friend with an older Bryston B4 with power switch issues.
 
If I don't have a 100 ohm 1/2 watt resistor on hand, could I substitute (in series) a pair of 50 ohm 1/4 watt resistors? One to the gate leg, and I was thinking of putting the second a few inches along the path, close to the receiver's venting. Heat shrinked, of course, but maybe with the bulb of the resistors uncovered, for air to dissipate heat.
Is that stupid. It's an SX 450.
 
The 100 ohm looks like a gate stopper to prevent oscillations or limit gate current. It will likely work fine with a single 50.
 
McFork said:
Awesome, thanks, Was just worried I was missing something obvious and stupid.
Click to expand...
If you want to be sure, try it and measure the voltage drop across each resistor. Then calculate the power dissipation in the resistor - P=V^2/R. Make sure it's under 1/4 watt.
 
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The timing for this resurrection is good. Making a switch box for a Citation 12. No power switch. A lot of big capacitors, so inrush is pretty healthy. Going into a project box, so the triac can be added after my next part order.
 
hopeless said:
The timing for this resurrection is good. Making a switch box for a Citation 12. No power switch. A lot of big capacitors, so inrush is pretty healthy. Going into a project box, so the triac can be added after my next part order.
Click to expand...
I think most modern, decent quality switches should be able to handle that amp...my understanding of the triac mod is to assist underqualified switches (mainly the ALPS, it seems) from buying the farm, so that the piece is still, essentially the same, with something added. Also the offending switches tend to be a rotating selector type, and I'm not sure if they're even made anymore, and why would they? They suck.
In your case, you're in control of the selection of switch, I'd say just pick a good one with the appropriate specs.
There've been a lot of posts about a speaker relay, and that may also be something to consider
 
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