Sony STR-6800 receiver - stiff tuning, dial lamps and...

[stevehertz]

Good idea David, I'll see if one of my mates has one that I can borrow. But as you say, it needs to have built in RIAA equalisation for it to work into an (the) Aux input.

[sp10mk11]

hmmm strange because I have used the same Ortofon devices with an MC-10 on mine without any problems like you mentioned.
The phono stage is next to the power amplifier board could it be possible that you have disturbed the wiring going to the phono stage whilst removing the power amp pcb.
If you have one to hand you could try a
Magnetic cartridge to see if the problem persists, if it does then it is obviously the phono stage at fault
Gary

Pic of the phono stage attached

[stevehertz]

Gary, when you say, "disturbed the wiring"? Surely the manner in which the wires are dressed is not critical? I wouldn't have disturbed them that much. Otherwise I'm in no rush on this as I don't often listen to records, mostly FM radio. But it has to be sorted. Substitution - as you and Gary suggest - will shed some light on things.

[sp10mk11]

Hello Steve by "disturbed the wiring" I meant broken a wire off of the PCB or maybe a component.
Good luck anyway
Gary

[stevehertz]

Thanks Gary.

Another point - is anyone getting bored yet BTW?! - the receiver has a hefty switch on thump. I've never 'liked' this kind of thing as it must stress bass drivers' surrounds somewhat and - I guess - ultimately reduce their lifetime. Now, correct me if I'm wrong, but aren't there two reasons for a switch on thump? The first being the power supply inrush current and general 'settling down' causing a DC voltage to appear at the output terminals. Is there a second one whereby there can be a standing (permanent) DC offset voltage at the output? In the case of the first, then building a small delayed relay circuit to connect the speakers will do the job, but in the case of the second type, then this wouldn't work it would merely delay the thump until the speakers were connected - am I right? I notice in the Hifi-Choice lab reviews of the Sony STR-2800 & 3800 & 5800 that they are all shown as having a DC offset (is that momentary or standing?), and in the case of the 5800, this is 40mV. Ok, mine's the 6800, but you can bet your life something similar is going on.

[sp10mk11]

That is not right at all, you should not have a thump at switch on at all, I am wondering if you have accidentily removed an ground connection some where if a stage is not grounded properly you could get this symptom which makes me wonder about the phono stage with its strange sound maybe a ground has come off it so it is not working as it should.
Do you get any thumps when you select different inputs or tape?
Gary

[Edward Huggins]

My God, this thread is now so long I get lost everytime I try to re-read it. Surely the PHONO stage on this receiver will already have RIAA equalisation as standard? Edward

[stevehertz]

Gary, it thumped from the day I got it a few weeks ago. And not wanting to be controversial, I have experienced many hifi amps that give switch on thumps, including brand new ones with 'nothing' wrong with them.

No, mine doesn't thump when switching between inputs.

[Goldie99]

Hi Steve - the schematic I have for the STR-6800 shows a protection / muting circuit & relay - are you saying yours 'thumps' when the relay closes, or literally as soon as you switch it on ? I assume the relay & protection / muting circuit is working properly ?

Did you try monitoring the speaker output terminals for dc offset, as you turn it on, and as the relay clicks in ? just to see what's happening. & when.

[sp10mk11]

Edward Huggins
Yes the phono stage has RIAA equalisation
Gary

[sp10mk11]

Goldie99
Good points you mention there, lets hope they bring some results
Gary

[sp10mk11]

Steve
yes in deed many amps can thump when you switch them on, but in the case of 1970s relay coupled outputs on Japanese amps unless there is some thing is wrong basically they don't thump.
Gary

[Edward Huggins]

My superb Pioneer A400 amplifier (dob 1990) gives a hearty thump when powered up. Good job it does - that red pilot light is so small.....Edward

[stevehertz]

Hmm. Now you mention it, when I was fixing it, I noticed that the outer two relay contacts on the PCB side had been shorted with wire links... I didn't stop to think what it was for at the time, but there you go. I'll remove the links in due course. But why would someone do that?!

[paulsherwin]

It's a bodge repair when something goes wrong with the protection circuit. Bad relay contacts or dry joints are the most likely fault but it could be lots of things.

You can leave it like that but the problem isn't the switchon thump - it's that your woofers will get taken out if the output transistors ever fail.

[stevehertz]

Right, just been to pick GF up from work and was having a think - as you do. As I said, the outer two relay contacts are shorted and.. the plastic cover for the relay was (is) missing, so someone has been having a good play around in this area. I guessed that maybe the relay was not operating so someone had shorted the relay out for that reason. But! just checking it out in situ, I turned the volume down to zero, stuck me head right next to the receiver, switched on (switch on thump) then after about three seconds the relay clicks in! So the relay is operating (unless there's another one in there?), so again, why did someone short it out? The receiver is not easy to keep moving in and out of situ (to put it mildly) due to its position on a shelf halfway up the wall, the connections at the back being very difficult to get at let alone make or break etc etc. So, I'm going to wait until I have done further testing wrt the poor sounding phono input, and attend to both issues at the same time. I'll remove those soldered links then anyway. Before I put it all back together last time I carefully cleaned and fettled the relay contacts, lined them up physically for equal pressure etc, so all contacts should be good now, if they weren't before.

And wrt the poor sounding phono, I'm begining to think that it's my grotty records that are at fault. That corner of the room suffers from damp issues (it's an old, cold house with no cavity) and on inspection the records all seem to have small amounts of surface mould on them to a greater or lesser degree. This morning I played the Eagles Hotel California album and at times the sound was quite good, good in fact. I moved to another part of the record and it was horrendous; high frequency hash and distortion. But the fact that - albeit spasmodically - it can sound 'good', I'm thinking there's no major issues with the equipment, it points to the mould growth on the records. Next step, borrow a known good record and play it..

[Edward Huggins]

Or just clean your records - properly. But this could be the start of a new thread... Edward

[paulsherwin]

If the relay is switching when it should then the contacts are probably dirty. The fact that the cover is missing suggests somebody was trying to clean them, presumably unsuccessfully. Replacement PCB relays are very cheap.

[stevehertz]

Paul, as I said earlier, I have already carried a thorough relay clean/overhaul (was one of my jobs as an apprentice in the company service dept!) so there's nowt wrong with it now. I'm expecting it to work fine when I can remove those links that some kind soul has soldered in.

I'm thinking it was maybe an audiophool who thinks that relays on the output of an amp 'get in the way of the signal path'... Dohhh. Other than that I cannot see for what reason the contacts may have been shorted? The relay 'operates' after all; I guess due to poor contacts it could have been causing intermittent speaker connections or something, but it seems crazy to link something out when you can just clean/service it properly instead! But hey, we're into bodgers domain now, or, the local repair shop where every minute used on a job is time 'lost'.

[stevehertz]

Originally Posted by Edward Huggins

Or just clean your records - properly. But this could be the start of a new thread... Edward

Well obviously, but that's ongoing. As I said, there's seemingly a mould problem, and it's going to take more than a cursory wipe over with a record brush (I exaggerate to make a point) to get 130 records clean and free from spots of surface mould. I'm currently checking out proper cleaners and also taking my whole collection to a Keith Monks machine facility. It will be done..