Sansui TU-555 power on issue

[Bert Beukema]

Hi guys, I'm the proud owner of a Sansui TU-555 tuner (which accompanies an AU-555 amp). I bought the set in mint condition some time ago, complete with the original boxes and materials. It's a fine set and i'm enjoying my little 'old school' happy place.

However my TU-555 tuner is experiencing problems now. Generally it won't switch on, nothing happens. Now, strangely enough, when I remove the fuse (1A) and play around with it then return it, sometimes it will power on. Then it's playing fine but after roughly 30 minutes it will power down again. And of course it won't turn on again. The fuse itself seems fine, it doesn't burn out. In my rather dusty electrical mind it does seem like a problem with the power, but i'm not sure where to start looking.

As these are old machines and 'power on' issues are rather common I was wondering if anyone could chip in with an idea? It might be a stupid thing (wrong fuse type?) or a big thing (blown transformer) but I'd rather not muck around it's insides without some peer guidance.

Thanks for thinking with me!

 

[mikstick]

It could be coincidence that when you play with the fuse / holder it starts to work, or it could be that the fuse and or holder is oxidised. Buy a new fuse and some switch cleaner. Keep unplugged and squirt some switch cleaner into the fuse holder once or twice and wait a good while before powering up. See if that helps

 

[Bert Beukema]

It could be coincidence that when you play with the fuse / holder it starts to work, or it could be that the fuse and or holder is oxidised. Buy a new fuse and some switch cleaner. Keep unplugged and squirt some switch cleaner into the fuse holder once or twice and wait a good while before powering up. See if that helps

Yes, it could be just a fluke of course (playing with the fuse). Let me try your suggestion first before escalating. Do you have a recommendation for the type of fuse to use in these machines? It's only rated at 1A but that was 40 years ago, it might be the case that a wrong fuse is used currently.

 

[Bert Beukema]

It could be coincidence that when you play with the fuse / holder it starts to work, or it could be that the fuse and or holder is oxidised. Buy a new fuse and some switch cleaner. Keep unplugged and squirt some switch cleaner into the fuse holder once or twice and wait a good while before powering up. See if that helps

Hmmm, this may be a complete dummy question but i'm wondering which type of fuse to use here. It's not on the board but in the back and the fuse that's in there now is a no-name no-spec fuse. Is a fast acting fuse good enough or should it be a quick acting one?

 

[LBPete]

Sansui sometimes put a sticker with the fuse rating on the board under the fuse. Other than that you would have to reference the service manual to get the fuse rating. If it's completely dead, no sound, no lights when it shuts down, it's probably a power supply issue and may be as simple as bad connections. For example, the fuse holder may not be holding the fuse tightly enough to make good contact. Tuner's don't draw a lot of power so a one amp fuse may be correct.

- Pete

 

[Bert Beukema]

I'm sure it's a 1A slow blow fuse, so i'm going to replace that one. I've opened the machine and for all intents and purposes it looks brand new to the untrained eye. It's completely clean and dust free, I can't see any visual problems such as corrosion or leakage. Of course that doesn't mean there is no problem but man, i've never seen something this old and this clean. To me, and i'm not a technician for sure, it looks almost brand new. So if the fuse trial and some contact spray doesn't work it has to be a component that has failed.

 

[LBPete]

Never use a slow blow fuse in audio gear! You want it to pop, the faster the better. You need to verify that the switch actually works. Do you have power at the transformer when the switch is turned on? Do you also have power on the output from the transformer when the switch is on?

- Pete

 

[Hyperion]

If you don't feel completely confident checking the things Pete suggested - it's better left to a pro - we don't want you getting electrocuted.

I have no idea of your skill level at this point. - Safety First.

 

[Bert Beukema]

Never use a slow blow fuse in audio gear! You want it to pop, the faster the better. You need to verify that the switch actually works. Do you have power at the transformer when the switch is turned on? Do you also have power on the output from the transformer when the switch is on?

- Pete

Hey Pete,

Thank you! The strange thing is, the fuse I got from the tuner is a very, very old one (the manufacturer doesn't exist anymore) and it is a Slow 1A fuse. I can replace it with a fast fuse of course, but the manual doesn't explicitly say that this is necessary.

As for the power switch. The unit sometimes switches on and then it works, if only for a short period (< 30 minutes). There is no 'sweet spot' for the switch to work, it's just randomly powering on. When the units powers down there is no indication something is wrong (such as excessive heat), the old fuse hasn't blown either. Of course, this may be because it is a slow blow fuse. When looking at the wiring, all seems to be okay, there is no decay or corrosion visible to the naked eye. There are no broken wires or soldering connections.

What would be your recommended steps in this regard? I do have my trusty multimeter but i'm unsure if that is enough to crosscheck the power lines.

 

[Bert Beukema]

I've made some photos from the unit's circuit boards, but they are very clean:

https://goo.gl/photos/ALJ5ct4hUkk1r42e7

 

[petehall347]

there looks to be some corrosion or something may have been spilled into the voltage selector switch .
you could try switching it a few times with the unit unplugged from the wall of course ..be sure to put it back where it is now in the 240v position .

 

[LBPete]

Look, this is just going around in circles. We understand the symptoms, we need facts. Do you have a multimeter and can you use it? You need to determine where the power drops out. It's a relatively simple task but, as John pointed out, you are dealing with voltages that can kill you. If you are not comfortable with that, you need to get it to a pro.

- Pete

 

[Bert Beukema]

Okay, I traced the entire board and the issue was with the fuse holder. I replaced the fuse holder in it's entirety with one from a donor and the system is now working like new again. Case closed ;-).