Tascam M520 Story...

[analogkid]

I think you are on the right track with the EQ... massive amounts of EQ are normally counter-productive to good tracks. Obviously you have to do some tweaking - but if you get solid tracks with a minimum of adjustments and effects, you will have far more options on mixdown. That is where the 520 should really shine!

The scratchy pots are annoying; if you have deoxited everything several times you may need to try some other things. Radio SHack still seels a product called TV Tuner cleaner - made for the old mechanical TV tuners that had hundreds of contacts in impossible to reach places, This stuff is HIGHLY pressurized, but it is a cleaner/lubricant combo, and may allow you to blast the dust and grit out of your pots and sliders. BE WARNED! It can be a messy process, but it might be worth your time to grab a can and try it on one slider or potentiometer just to see what happens. I have used some other tricks over the years to get the scratch out of a noisy potentiometer, but alas they either end up being temporary, messy, or involve products no longer manufactured.

AK

 

[sweetbeats]

Need help replacing VU meter lamps...anybody done this?

Earlier there was a post about having to pull the little metal caps off the ends of the old bulb to place on the new bulb...deseolder the end, squeeze the tip of the cap that has been crimped down on the bulb lead, loosen the bulb lead and then....

How are you supposed to safely get those caps off?? Mine are stuck to the bulb with some sort of adhesive...broke one bulb last night trying to pull the caps off.

 

[sweetbeats]

I'm changing some of my cleaning ideaology...

Well, I was hoping to be able to effectively clean pots and switches with the channel cards mounted on the face panel, but I think to do it right I am going to have to pull the individual cards out and do it...I've seen references to squirting DeoxIT into a pot from the bottom of it rather than the shaft side, and this could prove difficult with the cards installed. Plus, I found that it is much more effective to clean the latching switches by spraying the cleaner through a small hole that is toward the bottom of the switch housing on the side opposite solder-mount side. One little squirt and the switch fills up inside...so I'll definitely have to pull the cards to get to all of those...do it right, do it once. I thought my idea of dribbling DeoxIT into the switch down the shaft from the top would work, but not enough of the cleaner gets in there to do an effective job.

 

[dementedchord]

sorry didn't realize you were trying to do it from the top... i woulda said something sooner...

 

[sweetbeats]

No prob...I've had success doing it from the top on my MX-80...went from rubbing sandpaper blocks when twisting pots to totally quiet...I'd read about doing it from the bottom, I was just being stubborn I think. Didn't want to pull the cards off the faceplate if I didn't need to, both from a time standpoint but also to protect the cards.

Oh well. Its all a part of getting to know the unit.

 

[sweetbeats]

Updated cleaning methodology video

As a follow up to my last post, and to underscore dementedchord's (and many others over the years) implication that the only decent way to clean pots is to spray whatever cleaner you use into the pot from the bottom, I shot a video of how I'm cleaning stuff now.

Basically, the video I linked up in post #208 has a bunch of mediocre advice...thick skulled here.

Some points:

• Whereas before I was trying to avoid having to actually remove each card (for fear of causing damage getting it in or out and having it unsupported during cleaning), it is really clear now that, especially with the stacked pots, there is a great distance between the top knob and its associated potentiometer housing...There's no way the DeoxIT or whatever is going to make it down into the pot housing.
• I've already mentioned above my unsuccessful work with the latching switches, and the video shows what I anticipate to be a much more successful method.
• Cleaning the LED sockets...before, with the cards mounted, I didn't want to hose the sockets down because of the mess it would make down underneath. Well, I think that if you want your cleaning to be successful, liberal amounts of the cleaner are good (bearing in mind that you want to wipe up excess as you go and try and constrain the application to the component you are working on, i.e. having a piece of cloth covering the stuff you don't want sprayed). With the card out I can have it oriented upside-down so any cleaner applied that is excess runs off the top of the PCB away from components so like with the LED sockets you can shoot through and out the top rather than spraying down through and onto everything on the card.

Point is, get that card out of the mixer so you can really get the cleaner in where it needs to go and/or flush stuff out. Plus, if you are trying to clean pots from the top you risk washing more crud down into the pot.

I know this may seem like a "doh!" for many of you...this post is for all the people like me that just take awhile to figure stuff out for themselves and I'm trying to restore my misadvice from post #208. Go ahead and say "I toldja so."

Another thing I forgot to mention in the video is that the selector switches are well accessible when you get the card out too. These seem to be less susceptible to the maladies of the pots and latching switches just because of the mechanical design of them, but there is a hole in the face of the switch body just perfect for shooting in a blast of DeoxIT.

Anyway, here is the video:

YouTube

 

[sweetbeats]

Changing VU Meter Bulbs...ARG!

Well, due to the fact that Tascam used some sort of EVIL CEMENT to hold the metal caps on the ends of the original VU meter bulbs in the M-520, I had to basically bust the bulbs so I could chip and grind the glass out of the end caps. I even tried soaking the bulbs on acetone...didn't do a thing.

There's got to be a better way, but that's what I had to do...a couple minor cuts later I have caps ready to install on two of the new bulbs I bought...

 

[dementedchord]

...a couple minor cuts later I have caps ready to install on two of the new bulbs I bought...

that's why you make the big money...

 

[sweetbeats]

Livin' in the gauntlet, man!

 

[sweetbeats]

Replacing VU Meter Lamps Continued...

I think (hope) the meter bulbs Tascam sent me are the wrong ones. Look at the pictures below. The new bulb is the one on top in the pictures. MAN! I got all setup tonight to solder those caps on and then i see that the bulb glass as just about too short to actually be inside the caps if they are spaced right to fit in the bulb-holder in the meter.

I'll find out Monday...

 

[sweetbeats]

All they gots is the sorty ones...

FYI, all Tascam carries anymore are the shorter bulbs pictured above. The parts department told me that what people are doing is just soldering the bulb directly to the fuse type holder in the meter.

What I'm probably going to do, simply because I don't like the idea of soldering anything directly to my meters, is to go ahead and solder the the metal caps onto the short bulbs but hanging out enough to each the clips of the holder while providing some support to the bulb.

 

[dementedchord]

some boards dont use the holders... maybe remove them??? seems i remeber working on soundcraft/A+H/mackie boards where they were just soldered in... ymmv...

 

[sweetbeats]

Yeah, I think the bulbs in the little VU's on the 48 and 58 are soldered in...I'll probably try putting the caps on and see how it works...not comfy with modding the VU meters. Greenhorn here.

Though I will take a closer look.

 

[sweetbeats]

The results are in...

I finished cleaning up the channel card for channel #1 using all the new methods and got it reinstalled and tested it. AND....

Its pretty good...

• No scratchies on any pots except the TRIM pots. MAN! I must be gonna hafta HOSE those down with DeoxIT. But the rest of the pots are great
• No more flickering LED's (at least on channel #1).
• No more scratchy latching switches, although PFL and SOLO offer a little *click* in the phones when I press them, but maybe that's normal for that buss...plus that buss won't be printing to tape, so I'm probably gonna leave that one alone...

So overall it was a success except for the TRIM pots.

One observation/concern:

With the PHONES level knob at about 12:00, and if I'm monitoring, let's say AUX busses 1 & 2, it sounds like a waterfall. That is with the AUX send knobs at about 3:00 or 4:00, and the AUX masters for 1 & 2 set at between 7 and 8 (right around that "nominal level" gray band on the fader strip). Is this normal? I'd know better I guess with some program material at the input, but it just seemed really noisy...

 

[sweetbeats]

Pulled the channel card again...

Pulled the channel 1 card out again to try and get rid of the scratchies on the TRIM pots...shot them full of DeoxIT and shoestringed 'em x3. When I put the card back back in they're better, but not all better. Not sure if this means the pots are bad or if I just need to keep working at them...anybody have an opinion on that?

I also thought that I may have possibly missed applying DeoxIT to the SOLO and PFL switches which would explain why they "click" in the phones when I press them, so I applied DeoxIT to them and exercised them. Made no difference so I'm letting that one go. Everything else works great. On to channel #2.

 

[sweetbeats]

And 8 becomes 12...

Got all the VU's lit.

 

[dementedchord]

you've got a multimeter right??? if you dan get to that pot while it's hot see if there's some dc voltage on the lines... most of the time you dont see any dc just ac... so if there is some that could indicate a problem with the first stage of that pre... and that kinda thing can manafest as crackleing noise... you see it alot particularly with the tone section of guitar amps...

 

[sweetbeats]

Sorry for being daft...

dementedchord, its a little bit of a struggle but I can got to the pot while the board is hot. I did so last night, and there is DC voltage, but I'm not certain I'm referencing the right test points...

Honestly, I'm not quite certain how a variable resistor works and so I'm not clear on where I should be looking.

I did do some homework on it...studied the schematic for the channel card for over an hour...I have a little better understanding, but not enough to take your advice and truly put it to work, which I would really like to do...

To add to my confusiion there are actually 7 different channel PCB assemblies on the M-520, configurations A, B, C, D, E, F, and G. The schematic has a nice chart that lays out the differences between the different configurations. Channel 1, the channel with the noisy trim pots on my console, is configuration "A". VR1, the stacked input trims pot actually has 3 variable resistors on configuration A...If I'm looking at the schematic right, VR1 is the same as with the other configurations except that there is the third variable resistor, 10k(RD), that gets inserted into the signal path when sourcing the INST input (input "B" on the schematic) ahead of 10k(A). Is that correct? Its really confusing to me trying to read this schematic secondary to my lack of experience and the fact that Tascam decided to use one schematic for 7 configurations.

Whether or not I'm in the park on my understanding above, I'm still not certain which points to reference in looking for DC voltage. With a variable resistor there is one input current stream and two outputs? Do I look for DC voltage between ground and either of the output streams?

And another question: I'm not getting why there shouldn't be any DC voltage...isn't the input section powered by a DC rail??

 

[sweetbeats]

Back to bulbs for a moment...

I thought it might be valuable to post what I ended up doing with the VU meter bulbs to get them swapped out. I used hot glue to hold the metal caps on the ends of each bulb. That allowed the caps to be fixed in a position that was just at the ends of the bulbs to try and maximize the overall length, since the available bulbs are much shorter than the originals. There was a little bit of readjusting after soldering the caps to the bulb tails (from the heat...the glue liquified again), but having a cool damp rag cooled them down quickly while allowing me to hold the cap and bulb in position as the glue solidified.

They came out looking fine, and since those bulbs run so cool I'm not worried about the hot glue getting soft or anything.

Here is a pic of the bulbs installed in the meter assembly prior to putting it all back into the meter bridge:

And here is a picture of the two new bulbs with an original on the far left, and a bare bulb on the far right.

The new bulb assemblies are definitely shorter than the original, but you can see by the first pic that they fit well in the holders...plus there is very little if any variation in luminescence between the original and new bulbs as evidenced by the picture a couple three posts back of the full meter bridge lit up.

 

[A Reel Person]

That's...

sweet!........