Internal grounding issue with Teac A-3340S

[ofajen]

I've started tracking ideas to my Teac A-3340S. I've noticed a little thing that I would like to remedy and would welcome some help on:

I have an intermittent noise issue. It sporadically appears in the output of all four channels, more obvious in "source" than in "tape" position, but if it's there, it's there either way and I can record it to tape and play it back. The proper signal is not interrupted, but it's the kind of buzzy, grounding issue sound you get from a cable hooked into an amp input but not plugged into a source. If it's not making the sound, it can be induced by a few "pro audio whacks" on the back panel or front panel, and then can be temporarily knocked off again by another few whacks. If it's recording quietly and I hit the transport to stop and rewind, it may pop back on, and if it's making the sound when the transport is stopped, starting the machine into play mode may stop it. I really noticed it most (as in the largest transient at the time of the whack) when tapping the back panel where the audio go in and out and the power and ground lug are located.

Given that the machine has RCA outputs and the ground part of the RCA jacks relies on contact with that back plate and presumably some grounding scheme from that point to other key points in the machine, I'm assuming there is some kind of intermittent ground contact within the unit. Any thoughts as to the most likely culprits? Something in the power connection? The RCA jacks themselves? I've also noticed I can induce the noise (and then abate it) by removing or driving in screws that hold the lower and back panels in place or other screws holding the exterior frame pieces together.

Helpful suggestions are welcome!

Cheers,

Otto

 

[Dr ZEE]

grrr, this may be a tough one.

After I've read your post, the first thing I did I've checked if my machine has some sort of "extra buzz" at extreme settings. So I did listen with headphones through the mixing console. The only "noise" I am getting is if I push sliders on the mixer all the way up (that would hit the "red" if I'd play something or source/monitor something at "normal" input/output level (around "7" that is). And in this "situation" I only get a bit of hissy noise comming in if I pass "8" of the output pots. So, basically at "normal" levels, everything is dead silent. So, I would guess that you sure have some not-normal situation.

...

Given that the machine has RCA outputs and the ground part of the RCA jacks relies on contact with that back plate and presumably some grounding scheme from that point to other key points in the machine, I'm assuming there is some kind of intermittent ground contact within the unit. Any thoughts as to the most likely culprits? Something in the power connection? The RCA jacks themselves? ....

My machine has no side panels, as it's in the rack-stand, so I can see some stuff inside, and I've made couple of shots (see attached).
So, what I see is this: the input RCA jacks' ground "sleeves" are connected together in pairs, this is the soldering point where two shields of the signal wires are connected, the signal leads are soldered to the strips to 150K resistors, which are soldered to "tips" of the RCA(s) (see also diagram).
These shielded wires then are tied together with bunch of others (and I can't see much from where I "stand" ) , but they must go to Input Level pots, and the shields must be soldered there (to the "ground" terminal of the pot) and then from there the ground connection must be provided to the rec amp board, maybe also via shields.
It may be a pain in the neck to look through and try to find if there may be some sloppy connection somewhere there. It maybe between boards, or between board and pots ????? Not easy thing to do.
I don't know, man, good luck
here are photos and a cut from diagram:

 

[Dr ZEE]

...It sporadically appears in the output of all four channels,

Do you mean all the "same" on all four channels in unison? I'd imagine that you should monitor them in quattro , or in pairs with a very sophisticated panning and a sharp listening ..heh heh
Or do you mean that the noise appears in four channels but independently?

I am wondering here ... meybe the input pots are getting tired/and getting sloppy sort of speak.
hard to guess

 

[ofajen]

Do you mean all the "same" on all four channels in unison? I'd imagine that you should monitor them in quattro , or in pairs with a very sophisticated panning and a sharp listening ..heh heh
Or do you mean that the noise appears in four channels but independently?

I am wondering here ... meybe the input pots are getting tired/and getting sloppy sort of speak.
hard to guess

Yeah, I mean it's pretty much "all" or "nothing". Either everything is quiet, or the noise appears roughly in equal amounts in each channel output, a little more in "source" than in "tape" position, but will be audible in "tape" position, even if the transport is idle.

BTW, thanks for the pictures and schematic! Given the broad extent of where and how the noise shows up, I'm suspecting something very fundamental in the grounding connections within the unit, rather than something channel specific. Do you also have the schematic showing the outputs? If it isn't too much trouble, would you post that here, too? Meanwhile, I'll be pondering what type of failure could be causing this...

Cheers,

Otto

 

[Dr ZEE]

Otto, these diagrams are from photo-shots of 2340sx machine schematics, that SteveM emailed me some time ago. With few exception it's pretty much the same as 3340s. That's what I use when need to figure something out with 3340s . You can d-load the zip file of all "cuts" I have here (scroll down there in the list): http://www.mzentertainment.com/studio_workshop_technical_archive.html
********
I am attaching the cut of "output block".

As I see it, the base of "physical architecture" of the machine is such, so it's built as two sets of identical blocks/boards (1&3 and 2&4).... so if anything goes wrong with, let's say, a ground wire or a connector that goes to a board, then most likely the two channels will be affected. Then if it's a specific part/component, then only single channel will act out.
Also I still am not sure how exactly have you determined that ALL four channels in "unison" are "acting out". If you have a short period of time (comes in and goes away "type") noise, then it must be a tough thing to do - to catch listening all four channels "separately" at the same time for that short period of time... I mean you can listen to a pair of channels with headphones each panned left/right, or you listen to a mix of four channels, but then how do you know what is "the source of noise in the mix" .., unless it's so loud that you actually get visual meter reading on the mixer for each channel?????
OK, anyway, if you are sure that the noise is ALL across all four channels, and it's all exactly the same, then the only thing that come to my mind is that the "entire earth" of your machine is shaking, sort of speak... as the ground is the "common" for all four, and you get a "common for all noise", then it's must be the "main ground noise".
Do you have your Ground Post on the back of the machine connected to the Mother Earth? Mine is connected, but I've tried to connect/disconnect and I have not noticed any difference ... But I'd try this in your case and see if this would do anything.

The othere thing I would look into power supply block (or better say - associated with power supply areas ), check physical conditions there, connections etc

here's output "block" cut (keep in mind, that these schematics DO NOT reflect the actual architecture of grounding as it is in the machine):

 

[ofajen]

Also I still am not sure how exactly have you determined that ALL four channels in "unison" are "acting out". If you have a short period of time (comes in and goes away "type") noise, then it must be a tough thing to do - to catch listening all four channels "separately" at the same time for that short period of time... I mean you can listen to a pair of channels with headphones each panned left/right, or you listen to a mix of four channels, but then how do you know what is "the source of noise in the mix" .., unless it's so loud that you actually get visual meter reading on the mixer for each channel?????
(snip)
Do you have your Ground Post on the back of the machine connected to the Mother Earth? Mine is connected, but I've tried to connect/disconnect and I have not noticed any difference ... But I'd try this in your case and see if this would do anything.

Since the buzzing will start up either by me whacking it or some transport control change, it can last for a while if left undisturbed. And it can be gone for a while if left undisturbed. So, once it's on, there's usually plenty of time to unmute channels, and since I have the four channels panned symmetrically and at similar fader settings and I get a basically mono image, that tells me its there in all four channels. Usually, I also have time to switch from source to tape, though sometimes that switching operation is enough of a "nudge" to cause the buzzing to entirely disappear on all channels. I know that buzzing also shows up in the inputs because it tracks to tape, though I haven't yet tested all four channels in record mode at the same time to confirm that I can record four tracks of buzz.

I'll start with the ground post.

Thanks a lot!

Otto

 

[Tim Gillett]

Otto,

I think I'd take off the back covers and very gently move wires and connections until I located which item was the culprit. Sounds like a grounding issue. Possibly a bit of corrosion. Intermittent faults sure are a pain. Good luck!

Cheers Tim

 

[ofajen]

Well there is something going on in the internal grounding! I checked for continuity from the ground post to one of the output signal shields (the "ground" part of the TS plug of the output cable that plugs into my patchbay).

Sure enough, when things are good, the resistance reads a fraction of an ohm. But when I cause the buzzing, the resistance goes up to as much as 30 ohms. So, I guess I'll start at the ground post and work toward the outputs and see who looks guilty.

Cheers,

Otto

 

[Victory Pete]

This could be the perfect scenario for Deoxit! I think you are getting warm! Good luck!
VP

 

[ofajen]

This could be the perfect scenario for Deoxit! I think you are getting warm! Good luck!
VP

Thanks, but I don't think so. I/O contact issues would only affect a single channel at a time. This is a failure that commonly affects all inputs and outputs together.

Cheers,

Otto

 

[Victory Pete]

I was thinking you could use it to clean the suspected ground connections.

 

[ofajen]

Well, the problem now seems to either be gone or at least in remission.

I pulled the remote control plug and cleaned the contacts, but that didn't change anything.

The bottom and back cover panels are normally off anyway, but I took loose the rear chassis panel that houses the channel cards, I/O, ground post, fuse holder and such. I couldn't really move it far from the rest of the chassis, but just enough to get in and mess with a few things. Since I noticed this evening that the record enable switches seemed to be able to trigger the problem about as readily as anything, I focused on the relays. I mainly just wiggled and pushed on them. I also opened the fuse holder and securely put it back in place.

Whether from general fiddling, the fuse holder adjustment or fiddling with the relays, it seems the problem can no longer be recreated. My guess would be the relays. Anyway, now it's back to good working order. Cool!

Thanks for the help, folks!

Cheers,

Otto

 

[ofajen]

Whether from general fiddling, the fuse holder adjustment or fiddling with the relays, it seems the problem can no longer be recreated.

Unfortunately, it was just in remission. Maybe it was a temporary hiatus from having been opened up and then buttoned back together. Anyway, the buzzing noise now pops up again sporadically when I make switch adjustments to either record enable switches or source/tape switches. Still get the noise in all channels and in both tape and source position (or not at all anywhere). I reckon I'll open things back up and continue the search.

Cheers,

Otto

 

[Dr ZEE]

try this (see attached "diagram")

get a jumper wire cut, tie one end to the ground post.
then connect one output only to the mixer (disconnect all the others).
then "set" the machine in its NOISY state. heh heh, when you need it it may refuse to do so ..hah hah
So, say you've got the noise going. So you are listening to only one channel now.
Now connect (simply touch) the other end of the jumper with/to RCA's ground sleeve of the pair-channel of the output or/and then with the sleeve of input (of the same pair).
And see if the noise is going to go away, gets less loud (or get louder...???)

Drop a not about what you get this way
***********
p.s.

In case you completely give up on trying to make your machine to behave, you may want to contact Lt. Col. Spike Jones @ 1:25 and ask him to have a word with your "child" , ... after all Lieutenant does not wear his fancy hat for nothing , or does he ???

 

[ofajen]

For the last month or so, I was trying out miking the kick drum with a mike inside the drum. I didn't really get that much better of a sound, so I spent some time improving the sound of the drum by damping the resonant head and now I can get some sounds I like with mikes either overhead or out front.

What had really annoyed me was that all that super low bass from the inside the kick sound basically sounded like garbage on the Teac. Tons of bass modulation noise. The Teac does much better when I'm using mikes outside the kick.

So, I've fired the Teac back up the last few days and that buzzing noise came back, along with a new noise: an intermittent, loud thrumming from what seems to be the capstan motor. I could damp it totally by pushing on the front panel.

Anyway, I tried an extreme measure and turned the machine back up to a vertical orientation. I don't know if it's temporary or will stay this way if it stays vertical, but both problems have gone away, and at present I can't do anything in terms of operation of transport or controls to recreate either problem.

So, it would seem that my machine is much happier in the vertical orientation, so I think I'll leave it that way.

Cheers,

Otto