Diagnosing temperature related noise?

[Atmosferit]

Lockfit have a quite distinctive body shape.

Yeah, I've no see any such angled transistor components.

One thing I'm wondering though, is the variety of colors on the electrolytic capacitors: There are black ones, orange ones, a light blue one, a couple of purple ones, ... I'm half wondering if that's from the original design or if somebody already did some repair work on the deck, that could explain the smashed resistors and bent fuse holders?

I assume the noise symptoms also exist on the headphones output. Do you get the noise symptoms both with Dolby on and Dolby off ?

Pressing the Dolby or Chrome/Ferro button has no impact.

(Also of interest, when the sound crunches/stops, it's also reflected on the VU Meter properly like if it was part of the original sound)

I actually only tried on the Line Out, so from what I saw on the schematics, that makes the sound exit after the first filter and the dolby chip (NE5458), just before the preamp (TA7066P), I assume that would also happen on the headphone, I did not check because I could not find my 6.3mm jack adapter today

If the noise symptoms continue only to be on the left channel then that is good, as then you can monitor left and right signals (assuming you have a 2 channel scope) and that may make it easier to see the noise signal.

Yeah I've a two channel model, I'll try that tomorrow, I'll have to be careful because from what I see on the board/schematics, the 220 DC is actually going to the main board, which is why there are the two fuses and the four diodes rectifier bridges, I wish that had been neatly separated on another part of the tape deck.

[DMcMahon]

Tried to see the Playback/record switch in the manual, can see it in the block diagram but struggling to see it in the schematic. Also cannot easily see it on the mechanical drawing, item 43 is listed as the Record/PB actuator, if you can see item 43 on the drawing then the switch must be nearby I assume.

[DMcMahon]

Yes your personal safety is paramount ! be very careful.

[DMcMahon]

The AC voltage into the board itself is unlikely to be a high as 220 because the 2 bridge rectifiers are fed from the mains transformer secondaries, to produce correspondingly lower DC voltages.

However because it is not known what actual voltages are present at the transformer outputs and even a much lower voltage than 220 can be potential dangerous, assume that it could be as high as 220 and treat accordingly with respect.

[Atmosferit]

Originally Posted by DMcMahon

The AC voltage into the board itself is unlikely to be a high as 220 because the 2 bridge rectifiers are fed from the mains transformer secondaries, to produce correspondingly lower DC voltages.

However because it is not known what actual voltages are present at the transformer outputs and even a much lower voltage than 220 can be potential dangerous, assume that it could be as high as 220 and treat accordingly with respect.

I have measured 18 volts on one of the inputs, and 11.8 volts on the secondary, I unscrewed the mains connector and transformer block to get them out of the way, and there does not seem to be any exposed 220 connection point, it's all protected.

I tried to play a test sound from the line in, see if I could get it to play to the line out, tried with different combinations of record+play+pause, could not get the sound, so my next step is to use my 3000 hz sinus signal tape and play it directly on the device, and then check with the scope if I get my 3khz on the other side.

The main issue really is that this thing is super cramped and weirdly shaped: It's awesome as a decoration piece, but a bit of a pain to work on

[DMcMahon]

The transformer voltages being low is good (for safety).

Yes it certainly looks good but must be difficult to work on.

What is sinus ?

[DMcMahon]

I have experienced lots of different noise issues, particularly on older Akai R2Rs (older than your Cassette Deck) both constant and intermittent.

Many of the noise issue have been magically fixed by Servisol (or similar) switch cleaner spray application (not too much) to area's such as volume control, Source/Tape Monitor switch (don't think your Yamaha has this), Record/Playback switch and the various record/Playback calibration pre-set potentiometers (pots).

After cleaner application, exercising the item many times, also afterwards I like to leave the unit running playing music for quite a while, I think this may help dry up any left over residue.

Calibration pots are a somewhat difficult area to disturb as you do not want to upset the calibrations, not so bad if you have the relevant test tapes. When I do it I carefully note their physical positions of the pot wipers and to double check I measure their resistances both sides of the wiper. After any cleaning and exercising then putting the wiper back to the original position should then basically be in right ballpark position.
I personally then would tweak them if required as per set-up procedures.

I am not suggesting that you should clean/exercise your pots at this stage but maybe consider it later once other things have been checked but problem persists. By the way the pots I could see in your photos visually look good, they are often in a very dirty/tarnished poor looking state on many older R2Rs.

[DMcMahon]

Originally Posted by Atmosferit

Yeah, I've no see any such angled transistor components.

One thing I'm wondering though, is the variety of colors on the electrolytic capacitors: There are black ones, orange ones, a light blue one, a couple of purple ones, ... I'm half wondering if that's from the original design or if somebody already did some repair work on the deck, that could explain the smashed resistors and bent fuse holders?

Pressing the Dolby or Chrome/Ferro button has no impact.

(Also of interest, when the sound crunches/stops, it's also reflected on the VU Meter properly like if it was part of the original sound)

I actually only tried on the Line Out, so from what I saw on the schematics, that makes the sound exit after the first filter and the dolby chip (NE5458), just before the preamp (TA7066P), I assume that would also happen on the headphone, I did not check because I could not find my 6.3mm jack adapter today

Yeah I've a two channel model, I'll try that tomorrow, I'll have to be careful because from what I see on the board/schematics, the 220 DC is actually going to the main board, which is why there are the two fuses and the four diodes rectifier bridges, I wish that had been neatly separated on another part of the tape deck.

Very difficult to know about the different colour electrolytic capacitors, they will not necessarily all be the same colour, depending upon make etc, unless there is any obvious signs signs of new/later soldering work around them, I would not suspect there is a problem with them.

But it would not do any harm (particularly if there are signs of the soldering being disturbed) if you are able to while probing around, to check they are the correct values and polarised correctly (in right way around) but I do appreciate that this is much easier said than done.

Yes would expect to see the noise on the VU meter. Your circuit is not the easiest to find one ways around !

[Atmosferit]

I made a quick video of the oscilloscope showing the signal from the test tape ("Sine", not "sinus", sorry ) by reading at the line out, and got something similar on the headset output, so I guess I can eliminate the are around the preamp, it's most probably somewhere between the Dolby chip and the play/record head.

https://www.youtube.com/watch?v=lkycSuUibXc

(What happens is described in the description field, with timestamp links to the various sections)

I wanted to connect the two other channels to the record/play head yellow wire (around C2/R2/R18) but there's awfully no room to even approach the probes.

I'm thinking that maybe I should just solder some wire from the other side of the PCB, the main issue being that there is zero markings on the other side, so the probability of connecting to the wrong place is quite significant

[DMcMahon]

There is a lot going on in the scope results so not easy to comment, I can only see 1 comment in the description field ?

Presumably the horrible right channel trace at the beginning is the noise in question, so now showing on the right channel, yesterday was it not the left ?

At times there is quite a lot of general frequency instability on both channels when playing the 3kHz, some of this may be due to scope triggering/set-up and some of it could be fairly normal.

At times there is quite a bit of amplitude instability in the right channel with the sine wave, I assume this is due to the noise signal.

When you say you can eliminate the preamp did you mean phone amp (as its called on the block diagram) ?

[DMcMahon]

I can now see the full description comments, I did not see the "show more".

Is the volume control ganged or are there separate left and right volume sliders, as can see at times when you are adjusting the volume control you have no right channel sine wave. If both channels are ganged then interesting that at times you lose the right channel signal.

Unless playing the 3kHz test tape increases the likelihood of the noise being seen/generated, I would personally would just try and follow the noise back without the tape playing.

[ms660]

The schematic I'm looking at (manufactures manual on vintageshifi) appears to have several errors, so far as I can make out there's no bias supply to the Rec head, also the B+ supply for the RH Dolby IC appears to be wrong.

Have you tried scoping the input to the Dolby IC in the defective channel when in playback?

Lawrence.

[DMcMahon]

Yes I saw the apparent lack of bias at the record heads (shown on the block diagram of course) and thought I must be missing something, unusual for a schematic to be that incorrect !

[Atmosferit]

Originally Posted by DMcMahon

Presumably the horrible right channel trace at the beginning is the noise in question, so now showing on the right channel, yesterday was it not the left ?

It was the right channel at all time, just that I had the cable plugged the other way around (most CINCH/RCA are colored, but that one has two black connectors). (The VU meter confirmed that the problem was on the right, not left)

At times there is quite a lot of general frequency instability on both channels when playing the 3kHz, some of this may be due to scope triggering/set-up and some of it could be fairly normal.

Yeah, it's the scope trying to sync things: If I disable the right channel, the blue sine curve is steady.

When you say you can eliminate the preamp did you mean phone amp (as its called on the block diagram) ?

I mean the TA7066P

The schematic I'm looking at (manufactures manual on vintageshifi) appears to have several errors, so far as I can make out there's no bias supply to the Rec head, also the B+ supply for the RH Dolby IC appears to be wrong

I've only been using the ones in the Service Manual (which are annoying because not printed super clearly, and also reverted - as seen from the solder side instead of component side)

Have you tried scoping the input to the Dolby IC in the defective channel when in playback?

Nope, but that's a good point, I'll go fetch the pinout information and check that!

Is the volume control ganged or are there separate left and right volume sliders

It's two separate sliders that are easy to move together

Unless playing the 3kHz test tape increases the likelihood of the noise being seen/generated, I would personally would just try and follow the noise back without the tape playing.

That was my idea, it's easy to see that the signal is still playing, and the corruption is still quite visible.

Thanks for all the suggestions
Going to check this Dolby chip input.

[ms660]

Pin 5 of the Dolby IC is the principle input.

Pinout etc for anyone that needs it:

http://www.datasheetbank.com/NE545B-...DF-Unspecified

Lawrence.

[Atmosferit]

I miserably failed, I was able to get the signal probe attached to the pin 5, had to attach the ground clamp to some other exposed metal part (it's wayy to large to fit to the ground pin of the dolby chip without short circuiting anything), but I did not get any meaningful value (just a flat line) (obviously with the Dolby button pressed).

I was able to measure at least the voltage between pins 9 (ground) and 16 (v+) and got 12.2 volts on both chip (which is in the 10-20 volt range the datasheet mention)

Could anyone explain what these two push rod thingamagic on the attached picture are for exactly?

I know that if I press them while the oscciloscope is on, the signal goes all over the place, but I've been going through the service manual and I have still no clue about what they are for!

[ms660]

Originally Posted by Atmosferit

Could anyone explain what these two push rod thingamagic on the attached picture are for exactly?

I know that if I press them while the oscciloscope is on, the signal goes all over the place, but I've been going through the service manual and I have still no clue about what they are for!

They are the Record/Playback switches....One assembly per channel.

The contacts are numbered on the schematic (left hand channel)....1 to 27, they are shown in the Record position in the schematic, the switch contacts need to be clean.

Lawrence.

[ms660]

A correction and addition to my last post:

Switch contacts for the LH channel Rec/Playback switch are numbered in the schematic, starting at 1 and finishing at 24, there's actually 27 contacts in the switch, contacts 10, 11 &12 are not used, neither are contacts 25, 26 & 27.

The RH channel Rec/Playback switch also has 27 contacts, again contacts 10, 11 & 12 are not used but contacts 25, 26 & 27 are, they are numbered on the schematic and they enable the pitch control on playback:

https://www.vintage-radio.net/forum/...6&d=1580571188

Lawrence.

[Atmosferit]

Switch contacts for the LH channel Rec/Playback switch are numbered in the schematic, starting at 1 and finishing at 24, there's actually 27 contacts in the switch, contacts 10, 11 &12 are not used, neither are contacts 25, 26 & 27.

The RH channel Rec/Playback switch also has 27 contacts, again contacts 10, 11 & 12 are not used but contacts 25, 26 & 27 are, they are numbered on the schematic and they enable the pitch control on playback:

Oh my!

I've been looking for the pinout of these things all the weekend, I totally did not realize that this bunch of disjointed things spreadover the schematics were actually the pins of the record playback switch!

Mega thanks!

Now at least I can relate what is on the solder side with what it is on the schematics, and follow from "Record/Playback Head" to "Line Out".

I started poking with the probe, and I see that the voltage from the head is very weak (expected), but also apparently phase inverted compared to what is on the line out side, is that to be expected?

Another thing I will have to identify, is the correct values (and what they are for) of VR1/VR2, VR3/VR4 and VR11/VR12, because I would have expected them to be in the same positions, or mirrored positions, but they are not actually perfectly mirrored

Thanks so much for the help so far

[DMcMahon]

Changing the subject, do you like the scope ?

I have been thinking of upgrading my old Tektroinix for something more modern but am unsure about the all singing/all dancing modern scopes, though certainly would be very good to get the storage capability and nice to get 4 channels .