Any electronics hobbyist out there?

[orangecat]

I have an old Technics receiver that i really love but it's starting to show it's age and has a few electrical problems and I thought maybe someone coudl help me find out exactly what's causing the problem so I can fix it.

 

Here are a list of some of the problems it has...

 

1. Left channel cuts out sometimes

2. Left channel sometimes becomes distorted

3. Left channel sometimes doesn't output the correct power

4. Left channel sometimes has crackling and hissing when nothing is playing but disappears shortly after audio signal is present (I assume bad caps and they just need some extra current to charge up)

 

These are just some of the main problems the other problems are mostly just buttons need replacing or something needs to be cleaned.

 

All I really know about it is that it's real old and terribly inefficient. I uses Technics "New Class A" design but I couldn't find anything online that wasn't just people guessing. From what I gathered it could be one of a few possibly designs where it's class A until a certain power threshold then it switches to class AB for the efficiency boost. I also know it's supposed to put out 110 watts RMS per channel at 8 ohms but I've nearly cooked speakers rater for more so i think it's a bit underrated. The original spec for THD was about 0.005% but that's clearly gone out the window.

 

I'd really like to repair it and I would consider myself fairly knowledgeable about these kinds of things but I'd like a but of input to make sure I'm not a complete idiot.

 

The unit does work perfectly sometimes it's problems come and go. i think the problems come and go because of thermals on some of the bad components but without a proper schematic it's hard to tell what connects to what.

 

Also does anyone have any tips for buying replacement parts? I have tried looking online to match stuff liek capacitor values and stuff but it's hard to find the right stuff.

 

PS: The receiver is a Technics SU-V75 and it's not very popular since it's not the most high end or low end of products. Back in the day it sold for about $2,000 new and still sounds like it.

[MatthewEnderle]

Technics has used some bad MOSFETS before. My Digital piano had this issue. After playing a bunch of notes in the lower octaves it started to smell like electrical fire.

[Benjio]

It sounds like the issue with the left channel cutting out could be caused by the contacts corroding or wearing out on the relay. I'm having a similar problem with one of my receivers. In my thread (http://linustechtips.com/main/topic/428223-how-much-to-sell-non-working-receivers-for/) iamdarkyoshi was able to help me out a lot helping me choose a new relay and how to identify the bad one.

[orangecat]

Technics has used some bad MOSFETS before. My Digital piano had this issue. After playing a bunch of notes in the lower octaves it started to smell like electrical fire.

Mine gets really hot but it has never smelled like an electrical fire or as if anything was burning, though there are some dark spots on the PCB because some of the components handle a lot of power.

[orangecat]

It sounds like the issue with the left channel cutting out could be caused by the contacts corroding or wearing out on the relay. I'm having a similar problem with one of my receivers. In my thread (http://linustechtips.com/main/topic/428223-how-much-to-sell-non-working-receivers-for/) iamdarkyoshi was able to help me out a lot helping me choose a new relay and how to identify the bad one.

I'll try looking into that, the relay is definitely original and this unit has had allot of times when it was up to high for a long period of time and I'm sure the heat has gotten to it.

[Benjio]

I'll try looking into that, the relay is definitely original and this unit has had allot of times when it was up to high for a long period of time and I'm sure the heat has gotten to it.

You could try tapping the relay (might have to do it kind of hard) while its running to see if it affects the left channel at all. That would be a way to test if it is the relay or something else.

[orangecat]

It sounds like the issue with the left channel cutting out could be caused by the contacts corroding or wearing out on the relay. I'm having a similar problem with one of my receivers. In my thread (http://linustechtips.com/main/topic/428223-how-much-to-sell-non-working-receivers-for/) iamdarkyoshi was able to help me out a lot helping me choose a new relay and how to identify the bad one.

I found out the relay is rated at 125v 5 amps but I have no clue where I'd find that. I did a quick google search and I found allot that where under 5 amps and some that where way over in the 100s of amps.

[orangecat]

You could try tapping the relay (might have to do it kind of hard) while its running to see if it affects the left channel at all. That would be a way to test if it is the relay or something else.

I tapped it rather hard and it didn't knock the channel out.

 

Also heres a picture of it...

 

[Benjio]

I tapped it rather hard and it didn't knock the channel out.

Are you sure its the right one? My receiver had a couple relays in it. Also you could try when the channel is out already and see if it knocks it back in.

[orangecat]

Are you sure its the right one? My receiver had a couple relays in it. Also you could try when the channel is out already and see if it knocks it back in.

That's the only relay i can see and when the channel does go out it happens when it want to i can't really predict when it's going to happen, for example it's playing just fine right now with no problems but eventually it might fail but the next day it can work fine again. The best i got out of hitting the relay was it shut the entire amp off but i feel like that happened because the power button is broken and it might have jiggled the button around.

[Benjio]

That's the only relay i can see and when the channel does go out it happens when it want to i can't really predict when it's going to happen, for example it's playing just fine right now with no problems but eventually it might fail but the next day it can work fine again. The best i got out of hitting the relay was it shut the entire amp off but i feel like that happened because the power button is broken and it might have jiggled the button around.

Hmm okay. It may not be the relay at all then, I don't know. You might want to ask iamdarkyoshi to see what he thinks, he seems pretty knowledgeable. 

[Stefan1024]

I have an old Technics receiver that i really love but it's starting to show it's age and has a few electrical problems and I thought maybe someone coudl help me find out exactly what's causing the problem so I can fix it.

 

Here are a list of some of the problems it has...

 

1. Left channel cuts out sometimes

2. Left channel sometimes becomes distorted

3. Left channel sometimes doesn't output the correct power

4. Left channel sometimes has crackling and hissing when nothing is playing but disappears shortly after audio signal is present (I assume bad caps and they just need some extra current to charge up)

 

These are just some of the main problems the other problems are mostly just buttons need replacing or something needs to be cleaned.

 

All I really know about it is that it's real old and terribly inefficient. I uses Technics "New Class A" design but I couldn't find anything online that wasn't just people guessing. From what I gathered it could be one of a few possibly designs where it's class A until a certain power threshold then it switches to class AB for the efficiency boost. I also know it's supposed to put out 110 watts RMS per channel at 8 ohms but I've nearly cooked speakers rater for more so i think it's a bit underrated. The original spec for THD was about 0.005% but that's clearly gone out the window.

 

I'd really like to repair it and I would consider myself fairly knowledgeable about these kinds of things but I'd like a but of input to make sure I'm not a complete idiot.

 

The unit does work perfectly sometimes it's problems come and go. i think the problems come and go because of thermals on some of the bad components but without a proper schematic it's hard to tell what connects to what.

 

Also does anyone have any tips for buying replacement parts? I have tried looking online to match stuff liek capacitor values and stuff but it's hard to find the right stuff.

 

PS: The receiver is a Technics SU-V75 and it's not very popular since it's not the most high end or low end of products. Back in the day it sold for about $2,000 new and still sounds like it.

 

Ok, first of all class A means you only have one transistor doing the heavy lifting:

 

It is terribly inefficient since it allways uses the same power at idel as with a music playing at max volume. Since it is usually pretty hot inside the case the electrolyte condensators dry out over time. But normally a waek power deliverty would affect both channels. Do you have any measurement equipment and do you feel conftabe doing any measurements while the device is on? (Take care of the higth voltage circuit!!!)

 

The replacement capacitors should have the same capacity if possible and the same or higher voltage rating. The tollerance is not critical. Also you only have to replace the "big once". But the migth be quite expensive.