Denon DR-M10HX Cassette Deck Servicing Help

[Nevillet]

Hi All,

I have an old Denon DR-M10HX cassette deck and want to service it.
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. Equally when I play a 3.5KHz test tape it's hard to see the test frequency through the noise.

Any advise would be welcome.

[redwire]

Re: Denon DR-M10HX Cassette Deck Servicing Help

A dirty, oxidized Record-Play switch is a very common problem with cassette decks.
Spray some DeOxit or other PPE cleaner into the switch and move it back and forth a hundred times. Don't get spray on the belts! Check the other switches and potentiometers are not dirty.
Then, you bring out the scope if need be.

[budwich]

Re: Denon DR-M10HX Cassette Deck Servicing Help

probably no schematic for this, right? you are going to have to break into it and look for any labeling of voltages in and around some of the connectors / between the boards. Check those to see if they are correct.... and since you have a scope, check what those voltages look like (ie. how clean is the DC). Might give clues where a probably might be.
Next, once open, prehaps you might be able to get close to the outputs from the heads to look at what they are seeing at or near the pre-amp section. Go from the result.

One other question, does selecting / unselecting the dolby options change the signals that you see?

[Nevillet]

Re: Denon DR-M10HX Cassette Deck Servicing Help

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


What are your thoughts?

[Nevillet]

Re: Denon DR-M10HX Cassette Deck Servicing Help

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

[R_J]

Re: Denon DR-M10HX Cassette Deck Servicing Help

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

I was going to upload that manual but after looking at pictures of the deck's board and the manual's board layout, they were quite different. The schematic could be close enough to work with. I would start by scoping the output of the power supply DC voltages, (+- 12v?) they could be discrete components like the schematic or regulator ic's ie 78xx and 79xx
If the noise is on both channels it is usually something that is common to both like the supply voltages.

[Nevillet]

Re: Denon DR-M10HX Cassette Deck Servicing Help

The circuit board does not match the service manual. There is a discrete bridge rectifier followed by two 1000uF/25V caps. The image below is the trace acoss each of them:



Using a Peak ESR70 meter they each measure (in circuit) ≈ 994uF & 0.12Ω

I've recorded some music (MP3 so no HF above 16KHz) and here is a link:
https://drive.google.com/file/d/1Emi...ew?usp=sharing

[R_J]

Re: Denon DR-M10HX Cassette Deck Servicing Help

That service manual is for the DR-M10, not the DR-10MX, The wave form across the caps is the raw dc, it should then go into positive and negative regulator circuits. This is the place to check if the regulator and filter circuits are working.
Using the DR-M10 manual, you need to check the outputs (emitters) of TR353 & TR351, in this case + & - 9vdc

[Nevillet]

Re: Denon DR-M10HX Cassette Deck Servicing Help

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.



I have made a new recording of audio this time connecting a HiFi CD player directly to the inputs of the cassette deck. I have recorded some 'silence' before the music starts so you can hear the baseline noise.

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

[R_J]

Re: Denon DR-M10HX Cassette Deck Servicing Help

That noise is likely not from the power supply, but could be coming from the motor. I suspect the noise is there even if you hit play without any tape? if it is, use your finger to slow down the motor and see if the pitch of the noise changes, it could be coming from the motor.

[Nevillet]

Re: Denon DR-M10HX Cassette Deck Servicing Help

Slowing the motor does not seem to alter the noise. Even if I unplug the power cables to deck motors the noise remains.

[budwich]

Re: Denon DR-M10HX Cassette Deck Servicing Help

get a small hair dyer or equivalent. try carefully heating some areas up to see if there is any impact on your traces / output results.

[redwire]

Re: Denon DR-M10HX Cassette Deck Servicing Help

No way this cassette deck is getting fixed with random scope traces and sound clips.
You have to use formal troubleshooting technique, a bit of science, otherwise it's like walking into a casino.

Don't get lost listening to soundcard noise lol. The deck is all analog and sometimes SIGLENT adds it's own noise, unless your grounding is wrong.
Use a test tape with a 1kHz signal or music to troubleshoot the playback function. Recording a tape then playing it back requires everything to work and will not help narrow down what is going on, which section is dead.

Without a service manual, you'll have to pop the lid and post pics of the main board.

[Nevillet]

Re: Denon DR-M10HX Cassette Deck Servicing Help

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

I'll be back.

Thanks