424 Mk III repair diary | Colour- coding Schematics | Monitor buss

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This is some footage I shot on my bench and using camtasia as I analysed and colour coded the schematic in photoshop during the repair of a Tascam 424 mk III.
The unit was bought cheap as a spares or repair item from ebay. It was received with a missing PSU.
I was able to wire up a compatible PSU with thew help of 3rd island's vidoe on the subject;-
• Tascam 424 MKIII power...
After inital cleaning and testing I discovered the following flaWS;- one dead mixer channel; the headphones only produced signal in the right speaker in mono mode; the right side of the monitor meter was not responding in L-R mode,; the headphone volume knob passed signal but the signal did not get louder or quieter or louder as the knob was rotated.
The mixer channel was narrowed down to the fader using signal tracing with a home made audio probe and an external amplifier. On removing the fader it transpired the conductive plate and the slider were both faulty, so I wired in an equivalent fader from a scrap XR3, reshaping the plastic shaft with jewellers files.
I started off assuming that the issues with the right side of the monitor buss headphone volume had the same casue, but they did not. The rotary dual gang potentiometer for the headphone level was faulty (requiring me to salvage a compatible part from a spares donor) ) whereas the monitor buss issue was casued by a non-conducting section of track on the printed circuit board between the master fader and the monitor switch (which I resolved with a jump wire).
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10 окт 2022

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Комментарии : 21

@SISKworks Год назад

Really good. Love learning your process with these type of videos.

@Tetrakan Год назад

Thanks Mike

@flypieTV Год назад

1:30 that tune is a trip 🥹

@Tetrakan Год назад

Ha yeah its extra special played backwards...check out drome and the Brothers Nylon if you haven't already

@flypieTV Год назад

@@Tetrakan I haven’t but will- thanks for the tip

@oinkooink 28 дней назад

Funny. Roughly, I suppose, I have a similar thing happening on my 424mkiii. The Monitor Level knob does nothing...totally unresponsive. But I can control cue mixes for overdubs via each channel's Effect 2/ Tape Cue control knob. So not sure I even need the Monitor Level knob to work. I think I mentioned this on another of your 424mkiii vids.

@wd4187 Год назад

Not sure how I've never thought of colour coding things digitally. Literally been sticking sheets of A4 paper together and using highlighters which takes up most of the living room floor. Thanks for this! Housemates will be pleased!

@Tetrakan Год назад

Haha glad I'm bringing the Marie Kondo effect to your process!

@johnnybeaver8351 Год назад

Just found your channel, really fantastic to share all of this. I have a MkII and III that have some highly noise pan pots and input switches. Been researching this for over a week but can't find any definitive information as to the right way to approach these. There's apparently a big D5 vs. F5 DeOxit battle. :P

@Tetrakan Год назад

Thanks! There's probably more than one effective way to clean these things but the way I do it is shown here ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-0-jzX_Ly964.html

@rthoulouze 8 месяцев назад

Hi! Thanks for your series on the 424 Mk3 and your blog. I recently lucked out on a unit that was lacking a power brick. After making one with a center tapped transformer all functions I tried seem to be working. However I do have some issues with it. The tape playback sounds uneven across channels (line in monitoring sounds fine), channels 1 and 3 are muffled and the best sounding is channel 4. Meaning if I record the same signal on different channels, they all sound different when playing back from the tape. I have yet to test with a different cassette but I was wondering if you had any idea about that. I also have a problem with weird mechanical sounds (periodical clacking) near the cassette player when everything is actually stopped. That one is concerning, actually. I haven't been using it too much for fear of something blowing up on me. Lastly, there seem to be bleeding on the meters? Like, no actual sound is audibly bleeding on other channels but the meters will show signal on other channels when I'm recording on one while the others are set to off and on safe. No clue if this is normal. I'll take any pointers you might have, thanks!

@nohrtillman8734 Год назад

Just found your channel after resurrecting my 424 MKII from its moving box. Great stuff! I hope to find one of your vids to help with mine. Signal paths through the mixer are clean and strong. Meters 1-4 show 0 to +6 recording. Upon playback, meters 1-4 barely blip up. My machine has deep problems I fear. High speed, DBX on play and record, on one of the fancy new 424 Master type II tapes. Should be great but playback output is so weak I know something is wrong.

@nohrtillman8734 Год назад

Problem identified. After cleaning and demagnetizing, I wanted a quick test of channel input and playback. I used (and learned): A-iPhone with the lightning to 3.5mm adapter (don’t) B-RU-vid music video source playing on the iPhone (also don’t) Something in that combination drove DBX nuts! By the time the record head saw it, the clean, strong mixer signal was badly attenuated, mangled and muffled. A real instrument input recorded and played back perfectly. Track 4 has issues, but that’s another day. Live and learn.

@Tetrakan Год назад

Glad you’ve made progress. Remaining mismatches between playback and record levels can be addressed by adjusting trimpots on the bottom board. For good gain structure, make sure you calibrate playback levels before adjusting the gain on the record amplifiers.

@tortugasoccerful Год назад

I'm having an issue with my 424 where when I have microphones connected, they pick up radio frequency. I know its fm and I've tried multiple cables and mics. It does not happen when I use quarter inch with a guitar plugged in...

@Tetrakan Год назад

I haven't encountered that before. Is this while using the XLR sockets? Maybe the third strand in the balanced cable is disconnected within the 424, so the shield is acting as an antenna? I'm talking otu of my hat though.

@SISKworks Год назад

What do you mean by audio probe? Can you recommend a model?

@Tetrakan Год назад

An audio probe is a homemade "stethoscope" so you can hear whether an audio signal is present and healthy at a particular point on a circuit board. Essentially you're temporarily hooking up the circuit under test to an external amplifier, with thevnegative side of a mono input cable going to circuit ground and the positive side connected to the point under test. The absolute simplest form of this would be a guitar practice amp, a jack to jack cable and 2 crocodile clip to crocodile clip cables: one crocodile cable would go from circuit ground (let's say the casing of a fader) to the sleeve of the guitar lead, the other crocodile cable would go from the test point (let's say you wanted to establish whether audio was reaching the input pin of an IC) to the tip of the guitar cable - any audio signal present will now be playing out of the practice amplifier. In my case I have an old multimeter stylus soldered to the positive pin of a female rca socket and a crocodile cable soldered to rhe negative pin. I use the cheap nearfield monitors by my bench to monitor the audio. I also gave a low value capacitor wired between the positve side stylus and the rca socket to prevent any DC current hurting the amp or speaker of the nearfields - anything under 10 uf will allow frequencies within the range of human hearing to pass unmolested. If you checkout this video you can see my probe in use and I linknin the description to a pedal building site with diagrams on how to build your own ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-fVs0ALyEUMY.html

@SISKworks Год назад

@@Tetrakan oh ok. I get it now. Thanks for such a detailed response. For some reason I thought it was a special tool that sent a signal into the circuit and you would trace with a scope. Didn’t realize you were tracing with actual audio coming out of a speaker. So do you just use any audio source as input when testing or do you some sort of signal generator?

@Tetrakan Год назад

I have a signal generator which will produce 1khz sine waves etc for calibration tasks where the amplitude needs to be steady and I can use that to trace audio in a mixer where the cassette player is disconnected but it’s less jarring on the ears to use a prerecorded cassette with actual music on it where possible

@Tetrakan Год назад

I think at one time they sold audio probes prefabricated from realistic, Tandy those sorts of manufacturers but I’ve only seen them occasionally on eBay at ludicrous prices