What Does The 388 Use Sanyo LC4966 Semiconuctors For?

[Mark7]

There are four on the A buss PCB. According to the data sheet they're switching circuits. Wondering if a faulty semicondutor rather than a faulty pot is why I can't monitor Buss 2. I hope it is because i suspect the semiconductor would be easier to find a replacement for.

 

[sweetbeats]

Yes. I’ve seen a pattern of failures of the LC4966 in the 388 and the M-300 series consoles…enough that I think I purchased some at some point to have a stock of them here. There are several quad bilateral switch options in that package. The problem is all the other options, IIRC, have a maximum supply voltage swing of 15V, but in the 388 and M-300 consoles the logic switch ICs sit on +/-15V supply rails…30V total. So all the other options for parts cook if used. The LC4966 has a max swing of 40V. So it’s the only part that I’ve found that will work. There are NOS parts available online for ridiculous prices. I also see more reasonably priced parts available but I would be concerned about counterfeit parts…the risk they are a clone of some other quad bilateral switch and don’t actually have the same voltage rating. The other thing I think about is these ICs function in the circuit like four mini relays in one chip. Signal passes through them. So the quality of the part might matter more here than in other applications. So IIRC I went on a hunt for reasonably priced NOS parts I could trust were genuine. I found them at UTSOURCE…very reasonably priced, though they do have a minimum order and there are shipping costs, of course. For me that worked out fine because I had other parts I needed to get as well. But I just looked and they still have plenty of stock, and it’s the same stock from which I ordered my parts and I am confident they are genuine NOS Sanyo parts and indeed have a late-production date code of 2003, so they are likely about 20 years newer than what’s in your 388:

https://www.utsource.net/itm/p/1171...4szCHy2Sq-DLDfiiNdjjvu752Hy2IG5YO1k4xEnCKUq5h

 

[Mark7]

Is there any chance that the problem I've been having with monitoring PGM Buss/Track 2 is 4699 related? Because I really don't want to have to buy a replacement A buss board just to replace one unicorn poop rare bespoke Tascam volume pot.

 

[sweetbeats]

I already answer your repeat question in my last post. Please read.

 

[Mark7]

Would I need to replace all of them? How much is that going to cost? Is there a way to find the faulty one without desoldering them all from the PCB?

i missed the Yes at the beginning.

I really want to get this fixed

 

[sweetbeats]

Would I need to replace all of them?

That’s for you to decide. But first of all, remember, you don’t even know if the LC4966 is the problem. So first it would be good to learn if it is, and then decide if you want to replace them all. You should make your own decision. If it was me, if one has failed, and, knowing there is a pattern of these failing in this application at 40 years of age, if one has failed the others might also. I’d replace them all. But that’s me.

How much is that going to cost?

:|

The price for the parts will be whatever you pay for them depending on how many you get and from where you source them, and whatever other fees or charges are associated, plus any labor costs if you are not replacing them yourself. I already sent you a link to a good source for the part. You can see their pricing at the linked page. Did you look?

Is there a way to find the faulty one without desoldering them all from the PCB?

Again…we don’t even know any are faulty.

And in this case it is easier to identify if one or more seems to be faulty while they are still installed on the board by assigning test tone to the monitor paths and probing with your DMM at the outputs of the LC4966 parts. That’s how you suss out any signal path issues. This is no different. There are 8 monitor mixer channels. Each channel sources either the input path or the PGM channel path depending on the status of other things on the unit. So each monitor channel has two sources…8 channels…16 sources total for the monitor mixer, and that’s how we get to 4 quad switches…4x4=16. U109 does channels 1&2, U110 channels 3&4, etc. if you want to know if U109 isn’t working right, assign test tone to monitor channel 2, measure with your DMM to see if you have signal at pin 8 or pin 11 of U109…those are the inputs. If yes, then, when you should be able to hear that signal from channel 2, measure for tone at the outputs of U109 for channel 2, which is on pins 9 and 10. If you have signal at the input, and your controls are set to where you should be able to hear something from channel 2, and there is no signal at pins 9 or 10, then my suspicion is the part is bad.

 

[Mark7]

I did. Fuck that's cheap, Cheers.

So, I don't need to remove any parts but I assume I do need to remove the board. If only for the obvious reason that it's too cramped and dark to make the test with it in situ.
I think my DMM can generate some kind of test tone (there's a square wave symbol). But I've no idea how to use it (manual says nothing about it) What do I need to get?

 

[sweetbeats]

You know best if you need to remove the board. I can’t advise on that because I don’t know the physical constrains/circumstances you’re dealing with, so do what you need to do. The board will need to be fully connected unless you’re able to power it and inject test tone on a workbench, and my assumption is that is not the case. But if it’s too dark, you can always get more light. And if it’s too cramped sometimes the right kind of probes can still access what you need to access. But, again, you know your situation best.

I don’t know the first thing about your DMM and can’t get into helping you with that in a general sense.

You don’t need to get anything. This is basic stuff. Get on YouTube and search for test tone, or if you have a smartphone get a free tone generator app. You just need anything that plays a test tone and I usually use 1kHz for this type of thing; very common. The test tone is just convenient for troubleshooting because it’s a constant signal…it’s either there or it’s not…doesn’t vary. But you can use any signal, really. The other thing that nice about using test tone is that sometimes it’s helpful to be able to sniff the tone using a frequency counter, like if the level at a particular stage of the signal path is really low or the meter is getting confused by other signal or interference you can switch to the frequency counter mode and if you are, for instance, using 1kHz test tone the meter will pick that up and in the above circumstances be able to see the tone on the meter using the frequency counter. That doesn’t mean, if your meter doesn’t have that mode, you need to go get one. I’m just pointing out that option as an additional tool and benefit to using known frequency tone.