Tascam DM24 Repair

A few days ago I was able to purchase a DM24 for cheap off the internet. The problem was that 4 of the faders weren’t working.

This post is just a list of things which I had to do to make it work. Hopefully this helps people who have similar problems.

Issue 1: Screen Contrast
As mentioned everywhere on forums and tascamforums, the screen design is poor such that it tends to get hot and have a shortened lifespan. Over time the screen will ‘die’ either by having lines across the LCD or the constrast going too high and not being able to read the items.

After turning it on for the first time, I did notice that the screen was very difficult to read. I initially suspected a damaged/ageing screen, but after popping the lid, I found out that someone had in fact replaced the screen!

The screen was a ‘new’ non original factory one, and this was also apparent because the alignment of the LCD was off as the mounting points did not even line up, instead parts of the screen were ‘blu-tacked / plasticined’ on to the chassis!

By the looks of it, someone had already done the screen repair here:

http://tech.hamsterfight.co.uk/2016/03/tascam-dm24-screen-repair/

The state of the unit looks so similar to it that I’m sure the person who repaired this followed his guide. However I noticed that the resistors on the LCD were not ’27k’, it was instead 20k.

Short of a 27kOhm SMD resistor, I used a 6.8kOhm PTH type resistor and stuck it to the other end of the 20k SMD.

WP_20180114_003

Seems to have done the trick!

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Issue 2: Unit seems to be forever calibrating faders.

After a bit of searching, many users have said that the DM24 power supply is quite prone to failure – probably due to higher internal temperatures when opering for long periods.

Over time, the switch mode power supply’s capactiors will leak or bulge and eventually fail.

http://diato.org/sonotrad/

Alternate Link if broken

This website has links to information about DM24 issues too. It’s in French but there is a link: http://diato.org/sonotrad/DM24_condos.pdf, which is in English which describes the exact fault I was seeing. ”

“Starting Fader Calibration
⋅⋅⋅
## Don’t touch Faders ##”
The documentation mentioned that Revision 01 and 02 units should not be susceptible to this problem as Tascam had fixed the design by that stage.

 

WP_20180115_012

Having a look at my power supply (bottom right with the big choke) it was clear that it had the higher quality capacitors, and that I would not need to replace any caps here.

At this point I believed that the unit would fail to calibrate as there was something wrong with the faders. The person who sold it to me said that 4 of the faders were not working well.

As I understood and going into Diagnosis Mode, the faders do not respond if the calibration stage does not pass. Despite being able to select ‘Fader Tests’, the values do not change unless the calibration has completed.

I’ve fixed a Tascam TDM1000 before (LCD and Fader issues too…. coincidence or bad design?) and it turned out that dust in the faders was causing the wipers to not make proper contact.

I think this is a common issue among mixing desks and sometimes they’re in dusty environments or being used as a dinner plate…

So I took to removing the fader board and taking a good look at the faders. I find that you can’t measure the resistance of the fader while it’s in the board as you get a strange reading which goes from 0 -> 3kohms -> 0ohms over the travel of the fader.

I had to desolder them completely to test whether it was going from 0 to 5k. Surprisingly, the non working faders had their wipers making contact with the resistive tracks.

Use a pair of pliers to open up the fader and look at the wipers! They’re basically swimming in junk! At this point, it’s also a good idea to make sure the wipers are sticking up and making a good contact with the carbon strips, ovetime their spring along with dust and junk could cause them to be bent away.

I actually soldered the cleaned fader back in place and went back to testing it, only to find that it still did not work. At this stage I checked all the ribbon cables which connected to to fader board and the main pcb – which turned out all fine.

By now it was 1am or so, and I decided to swap out a known working fader (CH5) with a non working fader (CH6) just to test the signal path. Surely enough CH6 began working and CH5 stopped! So it must have been the fader!

Another look at the fader has a touch sensitive wiper which is supposed to connect somehow to the fader handle.

WP_20180115_009

Up close, you can see two sets of wiper pairs, one for the position track and another for the touch sense. On the touch sense pair, one of them is touching a metal plate which in turn is part of the metal fader handle. The other wiper makes contact with the touch sense track.

WP_20180115_010

Anyhow I noticed that there was an open circuit between the fader handle and the touch sense track output pin. Other working faders had readings between 10 ohms to 40kohms, a huge range, I guess the touch sense circuit works on a capacitive type sense so it would be very sensitive and be able to work with a wide range of input impedances.

I wasn’t able to push the touch sense wiper down any further to make contact with the metal plate, so I ended up just soldering it. This was very difficult, because the metal plate is part of the fader handle which acts as a heatsink!

After the touch sense fix, the unit seemed to work! Amazing! I guess the unit tests the touch sense circuit and ensures that it is working before continuing, as without it, you can end up fighting the motor and cause a burn out.

I’ve put it back together now, and it works really well! The DM24 certainly has a lot of features, so many routing options, and tons of more complicated options too….

Issue 3: Tact Switch replacement

I haven’t fully screwed it back together because I plan to replace the tact switches too which don’t trigger 100% of the time and that really annoys me. So in time I will replace them too.

There are two types of tact switches used:

TACT SW,EVQ11L H=5 TP  (2pin out)

https://www.aliexpress.com/item/100PCS-Lot-2-pins-6-6-5-mm-Switch-Tactile-Push-Button-Switches-6x6x5mm-Micro-Switch/32703078819.html

TACT SW,SKHHDA (Square top)

https://www.aliexpress.com/item/6-6-7-3MM-copper-pins-feet-touch-switch-button-switch-6-6-7-3-square/32606708331.html

I sourced these from aliexpress.

 

I hope this helps anyone out there wil DM24 issues.

Issue 4: Fader 8 travel & Fader 14 Smoothness

The unit is not completely perfect. I noticed that my Fader 8 calibrates very slow and I have to nudge it during calibration for it to finish. This fader also reaches it’s end sooner than the others, -infinity appears at around -70db on the fader scales.

After a few hours I discovered that somtimes, Fader 14 during Single Motor Test mode would jitter while moving up and down the fader. While the fader was relatively clean and the touch sense was not obstructed, my next thought was that the motor had a bit of dust / issue.

I proceeded to remove the motor from the fader belt and run it with a 1.5AA connected to the terminals both directions. In addition I also gave it a few firm spins with my fingers. My guess is that it would remove any dirt or oxidisation on any motor brushes.

This seemed to do the trick for both Fader 8 and Fader 14. So now I have the unit having full motor range as well as a quick calibration at boot up.

I hope that this is all the issues I will encounter!

 

8 thoughts on “Tascam DM24 Repair

  1. These fixes took a few days and at times very frustrating as I’d put it back together and then after a while another issue would crop up. I think due to the age of this machine many things will start needing repair.

  2. Nice fixes !
    I am the owner of http://diato.org/sonotrad/ and happy that it helped you.
    You also have some interresting information in AudioFanzine :
    https://fr.audiofanzine.com/console-numerique/tascam/DM-24/pedago/astuces/
    Yes they are in French, but with the help of a translator it is understandable… and with some help, I am ready to translate them, then post them here : https://en.audiofanzine.com/digital-mixer/tascam/DM-24/tutorials/a.record.html
    Bernard

    1. Thanks Berl,
      Yes I found out the French audiofanzine forums, I went through every single post too with Chrome Translate and made a post myself, as I was trying to find replacement pots, but have given up.

      I’m just waiting for some replacement switches to give the tact switches some new life.

  3. https://www.sweetwater.com/sweetcare/articles/tascam-dm-24-microphone-preamplifier-design-philosophy/

    TASCAM DM-24 Microphone Preamplifier Design Philosophy

    Article #15379 Updated on Apr 27, 2007 at 12:00 AM

    When the DM-24 was being created, its designers recognized that one of the biggest criticisms of earlier digital consoles was their lack of headroom when dealing with loud input signals, such as live drums. This lack of headroom would result in distortion as a result of clipping the mic preamp, with the signal level rising above the 0dBfs ceiling.

    TASCAM’s design philosophy on the DM-24’s mic preamps was to overcome this issue by providing preamps that could handle very high input levels without clipping, and without incorporating a pad which would color the sound. We’re proud to say that the customized preamps in the DM-24 achieved that goal. However, in doing so, some DM-24 owners have had difficulty at the opposite end of the input level scale: that of very low-level signals.

    For most people who record rock and pop music, the internal mic pres on the DM-24 have been highly praised. Also, with the availability of inexpensive, high-quality outboard mic pre’s, TASCAM felt that DM-24 owners who regularly dealt with extremely low-level signals (i.e., distance-miked acoustic instruments and the like) would turn to their external preamplification solution of choice. Additionally, when combined with the additional 10dB of gain available at the DM-24’s input fader and yet another 10dB of gain available at its bus fader, both in the digital domain, these extremely low-noise (-128dB) mic preamps perform quite well.

    At approximately 95% turn, the pre’s achieve about 55dB of gain. Most input signals will require between 20dB and 40dB of gain, a range within the 65% to 85% turn of the trim pot. If more gain is required, raising the input fader to +10 provides an additional 10dB.

    In cases that that require more gain for quiet instruments or distant mic recording, TASCAM customers have reported to us that they rarely record with more then a few mics at a time in these situations. When this is the case, another solution is available: simply plug your mic into an XLR input and take a standard 1/4″ unbalanced cable from the insert of your input to the LINE input of the next available input. This gives you the combined boost of two mic pres with no added noise, making the gain much easier to control while offering plenty of gain for these situations. This input is then assigned to a channel and used normally. This may seem like a strange thing to do, but it works perfectly and is easier than buying an outboard mic pre.

    Tascam polled dozens of DM-24 owners in regard to the mic preamps, and the grand majority them have reported that they find the DM-24 mic pres great-sounding and are happy with their performance compared to those on other affordable digital consoles. However, for those of you that do work mostly with very low-level signals and would like to change the taper on your DM-24’s microphone preamplifiers (and not turn to an external preamp solution), an option is now available. For a charge of $200, TASCAM will upgrade your DM-24 input modules to those found in our premier audio production console/recorder/editor, the $8999 SX-1 Digital Production Environment. The only difference you will find is that the gain is more evenly distributed throughout the turn of the trim pot. This upgrade does not “boost” the gain of the mic pre or change any specifications regarding noise or other audio performance. It simply improves the trim pots curve for a more even response.

    If you wish to have TASCAM upgrade the mic preamps in your DM-24, this operation must be performed at TASCAM’s in-house service facility. While you will pay for shipping costs to TASCAM, we will pay return freight costs. To initiate this process, please call 310-726-0303 and ask to be connected to TASCAM’s service department.

  4. Hello. I found your article and I am asking you for help. I have DM24 and I decided to clean one fader that worked incorrectly. I unplugged the record and soldered the fader. After cleaning and reassembly, no faders work when the mixer is started. I have connected everything as before and nothing moves. Help

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