TEAC A-3440 - Next steps -- Capacitor refurbishment.

hdp160

hdp160

New member
Hi everyone,

I've spent a few days stripping down the recorder, Cleaned, Lubricated, Changed belts and Reseated all the boards at the bottom of the recorder and everything is now working mechanically very well.

I intend now to move onto the electronics...
Generally everything appears to be functioning electronically FINE but a little bit below par.

The biggest problem I'm trying to resolve first is moderate sync related hum on channel 4.

(Tests below with NO TAPE INSTALLED AND CAPSTAN RUNNING)

With ALL inputs and Outputs set to zero and the master headphone volume set to Maximum and with SYNC selected I can hear hum through headphones when and only when channel 4 output is set to maximum.
Additionally,
With function select depressed on "any" of the four channels I can hear IN this hum the record warning led flashing.
This hum disappears when I ARM record. (and headphones are then nicely silent)

I'm guessing that this is going to be a capacitor problem or possibly a noisy relay.

Is there a list anywhere or video showing which capacitors should be changed on a recorder of this age (30+ years)

BTW I have circuit diagrams etc.
 
I've had a quick look at the circuit diagram and I'm """GUESSING""" the hum could be originating in the channel 4 "sync amp" if anyone could explain to me why when the record led is flashing it is affecting the sync amp i would be very grateful.

I think I will swap channel 4 and channel 1 boards over tomorrow and see if the problem hum moves from channel 4 to channel 1.
 
Last edited:
Well so far so good.. I removed all the sync amp boards cleaned them off thoroughly and reseated each one in a different slot and as expected the sync hum HAS disappeared and all channels are now nice and quiet.

The next problem to address is the artifact of noise generated by the FLASHING! record led (not heard when led is fully lit.) In channel 4 when it's output is at maximum, the headphone potentiometer is at maximum and 'sync' is selected.... Any ideas?

I have "dressed" the obvious cables in the vicinity of sync amp board 4 with no affect.
Additionally I have swapped all 4 of the REC/PLAY amp PCBs around, but the artifact remains on channel 4 through the headphones.
 
Last edited:
Fault located but not yet fixed....

Poor connection or dry joint near P130/P131 where the record/sync head leads attach to MOTHER board. Unfortunately I'm having a bit of difficulty moving the CONTROL board out of the way, it is not screwed in but there are one time black plastic clips which I don't want snap away today. Tomorrow I'll replace the clips with a few screws.
 
I have a 3440 but I am not sure how they generate the "flashing"? Way before such LEDs?
In any event, any pulse circuit is going to modulate a supply rail given half a chance so look for decouplers LOCAL to the flash circuitry.

It has been years since I studied the schematics of my machine and I forget how the PSUs are configured but if a bit primitive a sprinkling of 78s or similar regulators could help rather than refurbing old designs?

Bear in mind as well that this is TAPE FCS! Teac were probably not that fussy about getting hums etc much below tape noise and "weighted" noise figures help a lot in massaging specs!

Dave.
 
Is the noise of the flashing LED in the line out as well as the headphones?

The voice of reality answer: if the noise is not present in the line out, you are dealing with something that is only present in a cue monitoring buss...it won't be present in mastered material. Furthermore, you are hearing it when trims are at maximum (output level and headphone level), and we are talking about a complex electro-mechanical machine that is pushing 40 years old. It may be realistic you just put up with the noise as you may never actually hear it in a non-critical buss when levels are set to nominal positions.

Just something to consider. These things can be difficult to track down unless you have a scope, know how to use it.

Wait...[re-reading previous post]...you have found the location of the fault? How? How do you know there is a poor connection or dry solder joint on the joint PCB? Are you able to abate the noise by applying pressure to that connection or something?

If that's the case nice job getting this far...be careful poking around in there with the device powered...trust me, it's easy to unintentionally fry something.

It sounds like a possible shielding issue which could be a high resistance ground connection. So I guess keep at it what you are doing and report back.

General suggestion: when you are swapping amp cards around to see if a problem follows a card, don't swap them all around. Just do a pair at a time, otherwise you risk chasing your tail.
 
Your absolutely right living within the limitations of the technology.

I sold my scope a few years back, something which at times like this I regret, the easy way to find hums and clicks is as you say to follow the signal backwards.
Yes the "slight" click was/is leaving the machine via line out channel 4, that's why I eliminated the latter stages of amplification.

Looking at the circuit I couldn't see any obvious decoupling culprits, that’s why I'd decided to work forward from the sync/record heads.

As you correctly guessed I probed the hidden P130/131 connectors with my trusty nylon knitting needle and could make the LED artefact go away.

I bought the recorder last week on a whim and I'm looking forward to playing with it over the next few weeks.

BTW do you have a copy of the TEAC A-3440 >>>>"Circuit Description"<<<< manual? TEAC product number 510 326 30 apparently it is hard to track down (I've managed to download all the other A-3440 manuals and Les Carpenters guide.
 
If you probed the contacts with a metal probe the noise may have gone away because of the added capacitance of the probe vs a physical connectivity issue.

I'll have to check on that document when I have a chance.
 
I am still after a 12 pin rectangular plug for my recorder for the wired remote. Got it all working but with 30mm panel pins!

Dave.
 
You must log in or register to reply here.
Back
Top