Denon Cassette Servicing Help Please
 

Hi All,

I have a 20+ year old Denon DR-M10HX cassette deck that I'm going to try and service.

I have aquired some test tapes and I have a scope. When I connect the scope to the L&R line level outputs I see a great deal of high frequency noise before I play the tape. Equally when I play a 3.5KHz (or any other frequency) test tape it's hard to see the test frequency through the noise.

The 3rd & 4th image shows the noise with modulation.

Any advise would be welcome.

Many thanks

Re: Denon Cassette Servicing Help Please
 

I would say the first question is to see whether the deck actually plays known good music tapes correctly and also whether it records and plays OK. If it does then we have to start questioning the test and measurement setup.

A lot depends on the level the test tapes are recorded at as well.

So to begin with do not look to hard for problems... just analyse the deck as a whole as a typical user would.

Re: Denon Cassette Servicing Help Please
 

That's a very good point.

I don't have any pre-recorded factory made tapes but I have some new blanks so I can make some new recordings and assess the results.

I'll report back.

Thanks

Re: Denon Cassette Servicing Help Please
 

OK as a first off I've made some recordings from the line level outputs of the deck feeding a USB sound card directly and recorded in Audacity.

The 'Not Playing Noise - Raw' recording is just the background noise with no tape playing.
https://drive.google.com/file/d/14K3...ew?usp=sharing


The 'Not Playing Noise - Normalised' is the same recording but normalised in Audacity.
https://drive.google.com/file/d/1shd...ew?usp=sharing

The 'Blank Tape Playing - Raw' is a blank tape playing (not normalised)
https://drive.google.com/file/d/1vVC...ew?usp=sharing

And here's the service manual:
https://drive.google.com/file/d/1o5o...ew?usp=sharing


What are your thoughts?

Many thanks.

Re: Denon Cassette Servicing Help Please
 

Just make 'some tapes' of your own music; from a CD, computer, radio, whatever. Then, if the results appear to be poor in any way; dull, bright, wow, flutter, dropouts, distortion, etc etc, whatever, you can then use the test tapes to help you hone in on the problem. I just think you're going about it in the wrong way if I may say so.

Re: Denon Cassette Servicing Help Please
 

I'm with Steve on this - if it ain't broke, don't fix it - and as yet, you have not established that it's doing anything wrong. Just try recording and replaying some music on a decent cassette to start with and take it from there.

Re: Denon Cassette Servicing Help Please
 

I agree with Steve. Test tapes are for very accurate and fine calibration, not for basic gross assessment. They are not for " telling me all the problems with my tape deck". Back in the day test tapes were expensive and not to be used casually. We would not let one anywhere near a tape deck before having spent time getting the deck in good basic condition such that it wouldn't damage the test tape and ruin its fine accuracy either mechanically or magnetically, if that's a word. This included carefully demagnetizing the tape path. Have you properly cleaned the tape path? From listening to one of your recordings I hear a whining noise which may be related to your digital recording setup rather than the tape deck.

Re: Denon Cassette Servicing Help Please
 

Hi All,

This is a short recording made on the deck. The source is a CD player connected directly to the tape deck. I recorded 6 seconds of 'silence' before the track starts in order to hear the baseline noise.

https://drive.google.com/file/d/1Uf9...ew?usp=sharing

Re: Denon Cassette Servicing Help Please
 

There are two TO220 transistors close to the bridge rectifier and smoothing caps. One is a D985 and the other is a B794. The trace below is from the emitter pins.

https://www.vintage-radio.net/forum/...1&d=1622479037

Re: Denon Cassette Servicing Help Please
 

I've never tried to diagnose cassette deck problems in this way. Scopes can reveal all sorts of strange things, which may or may not be significant.

Re: Denon Cassette Servicing Help Please
 

Thanks Paul.

So what is the sensible forwards?

Any advise would be welcome.

P.S. I've demagnetized the head and all the metal in the area. The heads, capstan and pinch wheel has been cleaned with isopropyl alcohol

Re: Denon Cassette Servicing Help Please
 

OK - on the principle of "what have we got on the ship that's good?", the WAV sounds pretty creditable - a fair facsimile of the CD track, only marred by the crackle. First thing to establish is whether it is present on playback of a blank tape, preferably one not used on this machine, and whether it is on both channels. At first listen, it sounds a bit like motor interference, not something to which modern decks ae particularly prone, but possible if the commutator is dirty or the screening can is not earthed, for instance.

Re: Denon Cassette Servicing Help Please
 

I bought a pack of new tapes and when I play one back the noise is there.

As soon as the deck is powered up the capstan motor starts. If I disconnect the connector to the motors the noise remains.

Re: Denon Cassette Servicing Help Please
 

Please state if the noise or its nature changes if Dolby B or C is selected. It is possible
for the dedicated Dolby IC to be at fault - play mode. The only way to obtain an
absolutely silent blank tape is to use a bulk erase device.

Re: Denon Cassette Servicing Help Please
 

. Then it's that change we need to hear in a recording. Ideally the only background noise we hear from the deck playing a new unrecorded tape is tape hiss. But there will also be the deck's preamp noise which often sounds like tape hiss. Often some hum induced by the deck's mains transformer which is probably what we hear in your last sample. But something has changed between your "not playing noise" sample and the last one. The whining has gone and the hum mentioned now appears. It's important in testing to only change one thing at a time. Otherwise things can get very confusing. Your uploads also appear to be all mono. As it's a stereo deck hearing both gives us a fuller picture. Sometimes a fault appears in only one channel. If so that should be apparent in your samples.

Re: Denon Cassette Servicing Help Please
 

Sorry to drag things back to basics, but if this unit has a mechanical record-playback switch might it be advisable to exercise it (operate it a few times) and see if that causes the symptoms to change significantly with each subsequent operation of the switch? Up to a certain point in time the number one cause of erratic / unreliable behaviour and odd noises on cassette decks was a dirty record / playback switch.

If this particular deck has purely electronic record / replay switching, ignore the above.

Re: Denon Cassette Servicing Help Please
 

Sorry, busy life has got in the way of this for the moment.

I'll be back.

Thanks