Sony STR 6800SD

[Scott5591]

Originally Posted by Mooly

That's good news

Discolouration can be pretty normal on many resistors. Hard to say how important they are or what stress they are under without seeing what they do on the diagram.

i think the contacts on the original relay were beyond salvageable, i think replacement was the only option.

no wonder the receiver wasnt sounding too good

[Scott5591]

Originally Posted by Mooly

That's good news

Discolouration can be pretty normal on many resistors. Hard to say how important they are or what stress they are under without seeing what they do on the diagram.

heres the schematic Mooly, ive highlighted the resistors.

[stevehertz]

Originally Posted by Scott5591

i think the contacts on the original relay were beyond salvageable, i think replacement was the only option.

no wonder the receiver wasnt sounding too good

Those would clean up to be serviceable at least. But having a new replacement is obviously the better option.

[Mooly]

Originally Posted by Scott5591

heres the schematic Mooly, ive highlighted the resistors.

Thanks...

So they are simple series feed resistors to drop some voltage and ease dissipation on the series regulator transistors.

Do they say 1/2 watt on the diagram? Its a bit blurry. If so then that seems odd because I think it says 53 volts on one end and around 30 on the other. So 23 volts dropped across 560 ohm is 0.95 watt.

I'm going to say that if it were mine I probably would replace them. 2 watt metal oxide (or metal film) would be suitable. 1 watt is to close for comfort and they have obviously got hot in normal use.

Those contacts have seen a bit of action. Assuming the amp has never had a 'DC fault' and so had to break a current then the only way they could get like that is by turning the amp on and off every time with the volume up really high.

[Scott5591]

Originally Posted by Mooly

Thanks...

So they are simple series feed resistors to drop some voltage and ease dissipation on the series regulator transistors.

Do they say 1/2 watt on the diagram? Its a bit blurry. If so then that seems odd because I think it says 53 volts on one end and around 30 on the other. So 23 volts dropped across 560 ohm is 0.95 watt.

I'm going to say that if it were mine I probably would replace them. 2 watt metal oxide (or metal film) would be suitable. 1 watt is to close for comfort and they have obviously got hot in normal use.

Those contacts have seen a bit of action. Assuming the amp has never had a 'DC fault' and so had to break a current then the only way they could get like that is by turning the amp on and off every time with the volume up really high.

Thanks for explaining that to me Mooly , other than being able to read symbols and values schematics really hurt my head

Is there any good books or websites on schematics for beginners?

Yep they are 1/2 watt, if that’s the case why do you think Sony would do this? Purely from a cost saving perspective?

[Scott5591]

Originally Posted by stevehertz

Those would clean up to be serviceable at least. But having a new replacement is obviously the better option.

Plus it gives me piece of mind knowing it’s not something i’ll have to deal with again in the near future should it start acting up again

[Mooly]

Originally Posted by Scott5591

Thanks for explaining that to me Mooly , other than being able to read symbols and values schematics really hurt my head

Is there any good books or websites on schematics for beginners?

Yep they are 1/2 watt, if that’s the case why do you think Sony would do this? Purely from a cost saving perspective?

Tbh they look more like 1 watt from the picture (size and type) but the diagram does show 1/2 watt.

You would never specify a 1/2 watt part where it dissipates 1 watt, you just wouldn't.

It is possible for service manuals to contain errors, in fact it is quite common on older publications. You could for curiosity measure the DC voltage across the resistor and calculate the actual power dissipated yourself using the formula:

W=voltage squared and then divided by the resistance. So 23 volts across the resistor would be (23*23)/560 which is 0.944

One of the most highly regarded books is:
https://en.wikipedia.org/wiki/The_Ar...more%20rows%20

but it doesn't come cheap. The earlier editions would be perfect as well if you can get a copy.

[Herald1360]

Interesting wheel diagram. I think it's the only place I've seen power = R x Isquared- it is, of course, but it's normally put the other way round- power = Isquared x R.

[stevehertz]

Out of interest, I restored a Sony STR 6800SD a few years ago and it was covered here on the forum. You may find aspects of it useful or interesting.

https://vintage-radio.net/forum/showthread.php?t=123492

[Scott5591]

Originally Posted by stevehertz

Out of interest, I restored a Sony STR 6800SD a few years ago and it was covered here on the forum. You may find aspects of it useful or interesting.

https://vintage-radio.net/forum/showthread.php?t=123492

Thanks, I remember looking at that but didn’t realise it was you.

Think mine has a similar fault with the fm tuner, the right channel seems to virtually disappear after being on for half an hour.

Doesn’t really bother me though as I rarely listen to FM.

[stevehertz]

Originally Posted by Scott5591

Thanks, I remember looking at that but didn’t realise it was you.

Think mine has a similar fault with the fm tuner, the right channel seems to virtually disappear after being on for half an hour.

Doesn’t really bother me though as I rarely listen to FM.

You're not interested in fixing it? Mine was just a 330k resistor. From posts placed, it would appear that Sony had a batch of 'iffy' 330k resistors at that time, and my set had one in it. Worth pursuing, especially as you now have a strong contender for the fault.

[Scott5591]

Originally Posted by stevehertz

Out of interest, I restored a Sony STR 6800SD a few years ago and it was covered here on the forum. You may find aspects of it useful or interesting.

https://vintage-radio.net/forum/showthread.php?t=123492

I see you replaced the 2 560 ohm resistors in yours Steve, the service manual states a carbon film. Is it a good idea to replace these with metal film or metal oxide? Think I’ll change them to a 2W resistor as mooly suggested just to be on the safe side.

[Scott5591]

Originally Posted by stevehertz

You're not interested in fixing it? Mine was just a 330k resistor. From posts placed, it would appear that Sony had a batch of 'iffy' 330k resistors at that time, and my set had one in it. Worth pursuing, especially as you now have a strong contender for the fault.

thanks to Steves thread i decided to check mine for faulty 330k resistors.

looks like most of the ones on the pre amp board have gone bad with only one of them still reading okay

Thanks Steve