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 Forum index » DIY Hardware and Software » Thomas Henry designs
SN-Voice troubles
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lameth



Joined: Nov 21, 2010
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Location: Austria

PostPosted: Wed Mar 07, 2012 8:29 am    Post subject: SN-Voice troubles Reply with quote  Mark this post and the followings unread

Hello electro-music forum!

I finished my snvoice board the other day and started calibrating. First tried the Mixer Output -> nothing, so i went on testing. The result was no sound output from the 76477 only Tri und LFO were working as expected, but after consulting the schematic i knew they both have nothing to do with the 76477. Frustrated that the chip that i soldered directly to the board because in lack of an socket, was fried i stopped. Went on to read the data sheet and contruction notes that i found on the net and tested again today and now i think i know why there's no sound:

Pin 9 (System Inhibit) is always high because the Phase I Comp Out of the 4046 is high, so there's no sound because the systems is inhibited. Any Ideas why? faulty 4046?

And some other questions:
On the Mix Output i get a constant dc voltage with about 2v.

The ENV OUT has a voltage level about 0,05-0,15v p-p. is this normal?
The Attack pot is not to be turned else theres no ENV at all, whereas the Decay pot doesn't change a thing on the Decay time! (Only looked up on the osci, did not hear it)


Are there any Voltage Levels that i can test so that i can be sure the chip isn't fried?

Thanks
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State Machine
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PostPosted: Sat Mar 10, 2012 11:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Oh my, just saw this. I am not by my schematics (they are not in this computer) but will help. First, have any of your troubles been resolved since your last post? I know you mentioned that you did not socket the sound generator chip but usually the trouble is not the chip so don't fret my friend. Things like panel wire errors, PC board solder bridges, bent under IC pins ... etc., are the cause of most troubles. With that, look for silly things like that AND run continuity checks from your board to your front panel to double check your work. This may explain why some controls are not working at all.

Let me know then we will work from that point on.

Bill
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lameth



Joined: Nov 21, 2010
Posts: 6
Location: Austria

PostPosted: Mon Mar 12, 2012 7:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Bill,

thanks for the Answer.

I finished populating my second SN-Voice Board, this time after a night of searching successfully with an socket for the SN76477. Had much luck, the company is located in my hometown which made me very happy! Tested it yesterday and the second Board funtions properly so the Front Panel and its Connections are ok. YAY Smile

So i went on with the first pcb again, searched for solder bridges, scrubbed with an glasfibre cleaning pen so there should be no flux bridges, checked the IC legs and then compared the two boards.
The only difference i found was that i used 0,01uF Mylar for C8-C12 on the not functioning first board, on the second i have the 0,01uF Disc like stated in the BOM. IC's (except SN76477) swapping did not made any difference.
So i am down to two possible options i think: Either the capacitors or the SN76477 itself is the problem. I will desolder the Mylar and put the disc's in and hope Smile

I have attached a picture of the two boards, if someone finds another possible failure please let me know!

Thanks Gregor


FYI this company has the shrink dip sockets:
http://www.knap.at/
Link to the Sockets:
http://www.knap.at/produkte/steckverbinder/ic-sockel/326-327
they have very few on stock so you can not order in the onlineshop, just write them a mail what you need, very fast and friendly.
Didnt have the 28 pin version so they took some bigger socket and cut it into pieces, worked fine!


Board compare.jpg
 Description:
The two PCB's, First faulty one on the left side, second functioning one on the right side.
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Board compare.jpg


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State Machine
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PostPosted: Mon Mar 12, 2012 8:09 am    Post subject: Reply with quote  Mark this post and the followings unread

OK, now with this information, the capacitors will not make any difference in this situation. Let's focus on the sound generator SYS INHIBIT signal. This signal is derived by a couple circuits. Mainly the PLL chip, U2, CD4046. With no GATE applied to the SNV, pin 3 of U2 should be pulled to a logic high through R41, One input of phase comparator 1 of the PLL chip. The other input to this phase comparator, pin 14 SIGNAL IN, is Tied to the 5V power. Since the comparator is an XOR and is used as an inverter in this application, this output at pin 2 should be logic low at all times. Knowing this, let's take a voltmeter and just check that you have a logic high at pins 3 and 14 on U2. If not, just check connections and components around it. If they are both high and the SYSTEM INH is still high, then lets see if the sound chip is forcing it high by removing U2, gently bending Pin 2 up so that when the chip is reinserted, it will not connect to U1. Now recheck the level on lifted pin, 2. It should be logic low now. The U1 is most Likely the problem and is forcing this pin high.

Ok let me know how you do.
Bill
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lameth



Joined: Nov 21, 2010
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PostPosted: Mon Mar 12, 2012 10:31 am    Post subject: Reply with quote  Mark this post and the followings unread

OK thanks, glad i didnt start to desolder them!

Checked the levels with no GATE signal applied on U2 Pin 3 + 14, both high and Pin 2 is low. This is different to my measurements of last week where Pin 2 was always high. With GATE applied it jumps according to the GATE Signal. Maybe this was caused by a flux bridge? This is functioning normally now, but the Audio Out Pin 13 of U1 is again at a constant level of 2V, ENV is also the same as last week.

So now that U2 and the capacitors are ruled out as cause, the only explanation left is a defective SN76477 i guess? Or could this also be caused by a defective resistor/capacitor/transistor?

Thanks
Gregor
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State Machine
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PostPosted: Mon Mar 12, 2012 4:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK, so the system inhibit is a good logic level. Also make sure that pins 26 and 27 are logic low and the the pull down resistors, R64 and R65 (100K) are soldered properly in place. We don't want a float masquerading as a logic low. A float could look like a logic low and cause all sorts of havoc.

If you have not done this already, switch the sound generator to NOISE and see if you get that. If not, make sure, using an o-scope if you have one, the NOISE CLOCK is present at pin 3 of U1. This will also confirm that the PLL is now working. If the NOISE works BUT the VCO does not, the VCO could be driven out of its capture range and not oscillate at all. Thus, the problem may be at the expo converter and summing amplifier.

It looks more likely that your sound chip is at fault BUT covering many bases before you go and change it.

OK leet me know what your results are.
Bill
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lameth



Joined: Nov 21, 2010
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PostPosted: Mon Mar 12, 2012 8:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

U1 Pin 26 & Pin 27 are both low, Pin 25 switches with the Noise/VCO Switch, thats ok but i only get the 2V straight from the Out, no Pulse, no Noise. Noiseclock is fine at U1 Pin 3, yes checked with an Osci.

BUT when i measured the PulldownR's R64 and R65 they both showed only 42k which got me very confused because the colors indicate 100k. Very upset about my supplier i started measuring from the beginning and found these little bastards:

Resistor = Actual Resistance (Should be Resistanc)
R27 = 10k (47k)
R28 = 28k (47k)
R31 = 32k (82k)
R52 = 50k (220k)
R64 and R65 = 42k (100k)

Guess from now on i should check every Resistor before i solder it... Sad

But lets not get cranky!
schematics shows R27 is on the External VCO Control (U1 Pin 16),
R28 is on the Summing amp U4 Pin 9,
R32 and R52 are on the +15V Line of LFO and Tri OPAmp U4 Pin 2/6
and R64 and R65 are the Pulldowns but these should be the least Problem!

Your combination of thought about VCO and Summing Amp is very likely from looking where the faulty R's are so i will desolder these and give it another try!

Thanks
Gregor

edith says: desoldered the resistors and now they have their original value?! am i missing something about basic electronics? the value should be the same on the board as off or not????
guess i should get some sleep....
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Uncle Krunkus
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PostPosted: Tue Mar 13, 2012 2:55 am    Post subject: Reply with quote  Mark this post and the followings unread

No,
A resistor will always (nearly Confused ) measure lower than it's actual resistance when it's soldered into a board. Resistors always need to be tested with one end disconnected, otherwise the resistance of the rest of the circuit will be across the same two points.
Caps can sometimes be tested on the board, because you're usually looking for a short, but there may be many decoupling caps, so don't get fooled by thinking you know which one has failed!
So, no, a resistor's value is not the same "on the board as off" Smile

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State Machine
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PostPosted: Tue Mar 13, 2012 5:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Andy is correct, don't get fooled by the resistor values. They will in many cases read lower than their coded value due to it being in parallel with another resistance in circuit. Just brush up on some basic DC electronics. It's the old product over sum equation. Anyhow, it seems to me that it's time to yank that sound generator out, put a socket in your board and pull the chip from your working unit and try that one. You mentioned you had the other in a socket right? One thing though, Did you verify, before concluding that your noise was not working that your noise clock was indeed being generated by the CD4046 PLL IC and present at the sound generator input?

Bill
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lameth



Joined: Nov 21, 2010
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Location: Austria

PostPosted: Wed Mar 14, 2012 11:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes it's obvious that it doesnt have the same value, dont know what i was thinking. dont get much sleep atm with finishing my diploma, working, school, refurbishing the house and a little spare time for living and DIY!

Yes the Noiseclock from U2 Pin 4 was present on the Noiseclk Input U1 Pin 3 but definetely no Output from U1!

So i pulled U1 out, needed much time to clear the pcb-holes but finally i was able to stick the sockets in and got another SN76477 into the board aaaannnnndddddd YAY THERE'S SOUND! I can switch between Noise and Pulse Output, PWM Modes and the Locked Mode are functionable!

Only thing thats not as it should be is the Envelope Mode! ENV Out does nothing with GATE Signal applied to it except to give the before mentioned +2V on the Mix Output but no Envelope. ENV/Lock Switch does his thing switching Logic HIGH between U1 Pin1 and Pin28. In Locked Mode i get an Output on U4 Pin 14, throw the ENV/Lock Switch and the ENV Signal from U4 Pin 14 goes to 0V and the Mix to +2V.
Any Ideas on this one?

Thanks
Gregor
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State Machine
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PostPosted: Thu Mar 15, 2012 6:27 am    Post subject: Reply with quote  Mark this post and the followings unread

Assuming you check the state of the ENV lock bits and they are correct, in order for the chip to produce any sound with the ENV enabled, the SYS INH pin must be pulsed momentarilly to activate the one shot. When a GATE is applied to the SNV, Q5 collector goes low for the duration of GATE. C3 and R41 integrator turns this into a momentary low pulse, inverted by U2 and eventually outputs a short high going pulse on pin 2, SYS INH. From what I see, the pulse looks to be about 40 to 60 uS in duration. The internal one shot device is edge triggered and triggers on a high to low transition so the duration is not important but should be short to keep from detecting any noticible delay from GATE to sound production.

If you get this pulse at SYS INH but STILL no sound, make sure your ATTACK is set to MIN and DECAY is set to MAX and then try again.

One more thing to observe, make sure R40 (one shot control resistor), 100K unit, is connected correctly from Q5 COLLECTOR to U1-23. If this is not in place, the O/S will NOT fire correctly. R40 MUST pull to ground when GATE is applied.

OK, your next man !
Bill
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State Machine
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PostPosted: Wed Mar 28, 2012 9:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Any resolution ???
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lameth



Joined: Nov 21, 2010
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PostPosted: Wed Mar 28, 2012 9:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Sorry for my late Answer, didnt had much time last two weeks!

First of all i switched the two SN76477 between the boards and the failure stays on the First board. So U1 can not be the Problem.

Yes the ENV lock bits are correct, in ENV Mode U1 Pin 1 is HIGH, Pin 28 is LOW. The Collecter of Q5 goes LOW with GATE applied and the Pulse from C3 and R41 is created and goes into U2 Pin 2 on HIGH to LOW Level with a narrow pulse, inverted by U2 and goes out Pin 3 from LOW to HIGH with an duration of about 25 us to the SYS Inh of U1. Attack and Decay are set to MIN and MAX.

Also checked GATE Signal against U1 Pin23: they go vice versa, GATE HIGH = Pin 23 LOW!

Maybe a defective LF444? Have to buy another one to try, hopefully the next days but i am open to other suggestions Smile
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MCDELTAT



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PostPosted: Thu Aug 01, 2013 8:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

EDIT: RESOLVED (WITH LOTS OF SEARCHING)
The wire terminals are what I'm thinking is Manufacturer# 08-50-0032. Mouser# 538-"
Theres a lot of things that let me figure it out, first off I know the material has to be tin, then comparing the sizes with some that I have for Doepfer power plugs I knew the size had to be greater than 22-24, and lastly a subtle thing to notice is that the plugs I recieve have the "cat ears" on the terminal. So pretty sure of that one. Just wanted to document that if anyone messed up like me and needed more to complete a SN Voice or other synth.

---------------------------------------
I hate to rob this thread, but thought it would be better than create a new one to ask a pretty simple question.

Bassically, I messed up on the wiring by making some of the wires really short, so when I tried to plug the housing to the circuit I had a lot of tension. My resolution, I'm just going to re-do everything with ribbon(flat) cables. Pretty noob mistake.

Now the question is: What is the part number of the Molex wire terminals? I got to buy more. Theres so many on mouser I can't tell which it is.

Thanks for the help.
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