Help! The Source is killing me!!!

In a Moog Mood? Here's a forum for discussion of general Moog topics.
MOOG_NOOB
Posts: 8
Joined: Sun Jul 24, 2016 9:02 pm

Help! The Source is killing me!!!

Post by MOOG_NOOB » Sun Jul 24, 2016 9:29 pm

I recently 'stumbled' across a MOOG Source at a yard sale. Immediately new what it was and had to have it...$25 later it was mine. After getting it home I found that it 'basically' worked, that is, the factory programs all worked and it made sounds. However, not all of the 'tweakable' functions work. There are a few random buttons on the membrane panel that function properly (Prog. 1-16...in both Level 1 and 2 modes [including storing other programs to 16], Hold, MOD to OSC and MOD to Filter ON/OFF), but the remainder of the buttons have no apparent response and do not activate the incremental control. The EDIT led does not come on when I press any of the buttons except HOLD (which also brings up the : in the display). With HOLD on, the incremental control functions (although I do not know what parameter it is controlling...but I can hear a difference in the sound and the numbers in the display respond appropriately). If I hold KB Glide and hit HOLD I can get the glide function to work (including the SINGLE/MULT buttons and incremental control). I can also do this with a few of the Contour functions...but this does not seem to be proper operation.

I am an Electrical Engineer by trade, but I certainly would not call myself a Synth Technician. I have the schematics and have been pouring over them trying to solve the problem(s), but to no avail. I have tested the membrane and know that all of the switches work (tested with a custom built rig as well as plugged into the Digital PCB). I've also confirmed that all power supply voltages are correct...a 'Crazy Source' would have been too easy. I have tried to apply logic to my analysis...what's known to work, what's not...made some tables to look for patterns in faults that would help identify a bad logic gate or piece of circuitry. Measured voltages all over the place, swapped a few IC's...nothing seems to be getting me closer to the solution.

Here's where I beg for help. Any of the more experienced users out there care to give me some pointers (I'm decent with the analog side, but the digital aspect is testing my skills a bit). Also, if I start to pull out my last few hairs, can anyone recommend a good Synth Tech that has worked with Sources in the past...I'm in MD. Sorry for the lengthy post and any input is appreciated.

spiders
Posts: 26
Joined: Thu Feb 19, 2015 2:11 am

Re: Help! The Source is killing me!!!

Post by spiders » Mon Jul 25, 2016 12:31 pm

Hey Man, cool out. You just got a source for 25 bones. That's insane. Of course it isn't going to work right :D I paid way more and mine went absolutely loony immediately after I got it and left positive feedback. No, it wasn't the power supply.
Have you cleaned out the connectors where the membrane plugs in? Be careful, as you can easily remove the trace from the ribbon. My membrane took a dive and was hardly working at all and I fixed it with one of those conductive ink pens I had scoffed at forever. I just painted over the traces and let it dry for 24 hours. It's been working fine for around a year now. I'd say it's worth doing even if things are fine, those pens cost like 5 bucks. If working in this area changes your situation positively, that was your problem. Keep cleaning till the thing wakes up.


Did you check the edit latches?



Good luck

MOOG_NOOB
Posts: 8
Joined: Sun Jul 24, 2016 9:02 pm

Re: Help! The Source is killing me!!!

Post by MOOG_NOOB » Mon Jul 25, 2016 1:58 pm

Yeah, I certainly can't complain about the price...pretty much stole it.

I've checked the membrane a bunch of different ways and I am confident it is working correctly. I measured the resistance of each switch with it disconnected from the PCB (hence the custom rig) and with it connected to the PCB (measuring from the pull-up resistors to the anode of the diodes...which includes the connector resistance). I also measured the voltage drop across each of the switches when closed. The resistance and voltage drop varied a little, but the high and low ends of the measurement range occurred on switches that were working properly so I don't think that's the cause of the faulty switches.

I haven't replaced any components yet, best I can tell, this thing is completely unmolested and I'm the first one to remove the screws. I want to keep it as original as possible (but I also want it to work properly). I have swapped a few of the socket mounted IC's around to see if there was any change in performance or operation...this included the edit and program latches, as well as the latch in the membrane circuit and the two in the Synth Output circuit (U11 and U12). From the schematic it looks like the edit and program latches are used to set the value of the displays. Since the displays work properly I assume that these are working properly as well. I will probe around a little more to and check the latches anyway. Maybe something in there is causing the data bus to hand up for some reason.

I'm sure I'm overlooking something simple, but so far the data that I've been able to gather hasn't lead me anywhere.

I appreciate the input.

synthchaser
Posts: 7
Joined: Fri Jun 17, 2016 10:06 am

Re: Help! The Source is killing me!!!

Post by synthchaser » Mon Jul 25, 2016 2:04 pm

If it's killing you, I'd be happy to take it off your hands for $50. Double your money and save your frustration! :)

spiders
Posts: 26
Joined: Thu Feb 19, 2015 2:11 am

Re: Help! The Source is killing me!!!

Post by spiders » Tue Jul 26, 2016 2:35 pm

Well, from the sounds of it you are more solid than me in terms of electronics knowledge. There is little I can offer you there. I can say that the most simple things are often the cause of big problems, think small in the troubleshooting. Dirty legs of chips, things like that.

check the status of U26. Seems to have it's finger in a lot of pies. Also u5, which you have probably already done...............

Almost every chip on the computer is still available and quite cheap. I know this because after my source broke for the millionth time I just shotgunned the computer, replacing everything but the edit latches and the mod interface. I think it cost me around $60. I know this is not the most sound tech strategy, but the synth has been trouble free for a year now.............so whatever. You could save yourself a lot of head scratching and just start rechipping the board, starting with the things that seem most relevant on the schematic. Component level troubleshooting is fun, to a certain degree, but as I know very little about 1980 computer tech, it quickly got less fun the deeper in I went.
As far as keeping The Source original is concerned.........none of those digital components have any sort of vintage value beyond "hey, this is cool." The z80 is obviously an important piece of computer history, but they also manufactured a squillion of them. Yours is not a snowflake. A working source with new chips is way more valuable/useful than a marginally functioning original one. (It sounds to me like your processor is fine, though.) If you like, keep the chips you removed so that your synth can be returned to it's original status if you ever desired to do so.

That's my spiel. I'm sure there are some folks who would disagree with me on here.........which is fine.

Stevie Ray
Posts: 254
Joined: Sun Apr 17, 2016 2:25 pm

Re: Help! The Source is killing me!!!

Post by Stevie Ray » Tue Jul 26, 2016 8:02 pm

Well that's going to be a labour of love for sure. I agree with Spiders, re-chip every chip that you can. Check that the power supply is working properly and within its design limits.

MOOG_NOOB
Posts: 8
Joined: Sun Jul 24, 2016 9:02 pm

Re: Help! The Source is killing me!!!

Post by MOOG_NOOB » Wed Jul 27, 2016 9:54 pm

Thanks for the input.

I'm quickly approaching the 're-chip' strategy as I've exhausted a lot of the simple avenues and I am reaching the limits of my knowledge of 80's 'high-speed' bussed address/data systems. On the up side, a lot of things seem to be working properly.

Can I get a sanity check from the other Source users out there?

When you turn the unit on, it comes up in 'normal' mode...Program 1, edit light off. As I understand it, I should be able to push any of the light blue buttons to...let's say, change wave shape. The edit light should come on. If I push a yellow button, the edit light should come on and I can use the incremental control to change the value. If I push the HOLD button it should display the : symbol and lock down the membrane buttons except the STORE button and 'push and hold to review programs' feature.

Mine seems to work in reverse...when I initially turn it on, the edit light is off. It only comes on when I push HOLD (along with the : symbol). With HOLD (and the edit light) on I now have access to the incremental controller (it changes the sound, but I don't know which parameter is changing)...If I push something else, like KB Glide and hold it down...then push HOLD, I'm able to use the incremental controller for that function (works with Contour and Filter functions as well).

Where I'm stuck now is trying to figure out what's locking me from editing in 'play' mode and giving me some amount of (albeit screwy) access to various functions in HOLD mode.

Maybe I should try playing it in the mirror or while standing on my head.

Anyway, thanks for the advice.

User avatar
_DemonDan_
Posts: 1253
Joined: Mon Nov 16, 2009 4:52 pm

Re: Help! The Source is killing me!!!

Post by _DemonDan_ » Wed Aug 03, 2016 9:47 am

I tried, but I couldn't stop myself...
Attachments
THE-SUSPENSE.jpg
THE-SUSPENSE.jpg (20.29 KiB) Viewed 3068 times
_ :twisted: _DemonDan_ :twisted: _

Stevie Ray
Posts: 254
Joined: Sun Apr 17, 2016 2:25 pm

Re: Help! The Source is killing me!!!

Post by Stevie Ray » Wed Aug 03, 2016 5:43 pm

MOOG_NOOB wrote:Thanks for the input.
Mine seems to work in reverse...when I initially turn it on, the edit light is off. It only comes on when I push HOLD (along with the : symbol). With HOLD (and the edit light) on I now have access to the incremental controller (it changes the sound, but I don't know which parameter is changing)...If I push something else, like KB Glide and hold it down...then push HOLD, I'm able to use the incremental controller for that function (works with Contour and Filter functions as well).

Where I'm stuck now is trying to figure out what's locking me from editing in 'play' mode and giving me some amount of (albeit screwy) access to various functions in HOLD mode.

Maybe I should try playing it in the mirror or while standing on my head.

Anyway, thanks for the advice.


If you're seeing this kind of behaviour then I really think you need an expert on the Source (I'm not). Have you approached Moog? I know the product is more than obsolete but I have always had good technical support from Moog even when the product has been out of production for years. It's worth a shot anyway.

In your case I suspect it's a failure of the panel components (buttons etc.) rather than the main board. Double check the connectors and cables.

*** EDIT ***

Make ABSOLUTELY SURE that all the ribbon cable headers are correctly orientated and aligned!!!

MOOG_NOOB
Posts: 8
Joined: Sun Jul 24, 2016 9:02 pm

Re: Help! The Source is killing me!!!

Post by MOOG_NOOB » Thu Aug 04, 2016 6:19 pm

Thanks for the advice on contacting the company...I didn't think they would be able to help, but it's worth a shot.

I wish it were as simple as the switches or connectors...I've pushed each button while measuring voltage and resistance on the board (which is with the ribbon connectors in the circuit) and they're all good...plus I have some functionality on the buttons, just not correct functionality.

I'm waiting on about $30 in chips to be delivered...maybe I'll get lucky.

It seems to be 'locked' from editing programs at the wrong time. I'm currently working through the circuit backwards from the edit LED which comes on when the Hold button is pressed (it shouldn't). Hoping to find a bad inverter or decoder. CPU and EPROM seem to be working otherwise, so I'm hoping they're not the problem.

Thanks for the help.

spiders
Posts: 26
Joined: Thu Feb 19, 2015 2:11 am

Re: Help! The Source is killing me!!!

Post by spiders » Sat Aug 06, 2016 9:46 pm

Yeah, I'm curious as to how this one pans out myself. A friend of mine made a copy of the EPROM code for me when I was at the beginning of fixing my source. So, I can probably hook you up with that, just have to send him an email. I have code 2.0. PM if this would be of service. You would need an EPROM burner.......
In terms of an expert on the source, those are few and far between. Kevin Lightner (RIP) would have been a boon to you. There is a user here, MC, who knows an awful lot about them, you may wish to reach out to him. He is an EE as well, so maybe y'all could swap war stories.

Sometimes when I'm in the depths of a seemingly impossible repair I take a breath and remind myself that it's just something broken in there. It can't hide forever.

MOOG_NOOB
Posts: 8
Joined: Sun Jul 24, 2016 9:02 pm

Re: Help! The Source is killing me!!!

Post by MOOG_NOOB » Sun Aug 14, 2016 8:19 pm

Thanks for the help. Unfortunately work has me bouncing around the country the past few weeks, but hopefully I will get some time to stare at the schematics some more soon. My source has version 3.2 firmware so I'm not sure if 2.0 would run with the hardware configuration (I know there were a few I/O changes, but not sure what else). I've replaced a couple of chips on the digital PCB with no change in performance...I've also run it with the two digital PCB to synth PCB ribbon cables disconnected and the switches still work the same, leading me to believe it's an issue on the digital PCB. That was my suspicion, but little bits are helping me confirm it...now I just need to spend some time with the scope and meter to narrow it down. When I'm done maybe I'll write a book!

User avatar
MC
Posts: 2874
Joined: Tue Aug 12, 2003 2:20 pm
Location: Secluded Tranquil Country

Re: Help! The Source is killing me!!!

Post by MC » Mon Aug 15, 2016 12:40 am

Thanks for the mention, but at the moment I am very busy with family issues.
Gear list: '04 Saturn Ion, John Deere X300 tractor, ganged set of seven reel mowers for 3 acres of lawn, herd of sheep for backup lawn mowers, two tiger cats for mouse population control Oh you meant MUSIC gear Oops I hit the 255 character limi

Stevie Ray
Posts: 254
Joined: Sun Apr 17, 2016 2:25 pm

Re: Help! The Source is killing me!!!

Post by Stevie Ray » Tue Sep 06, 2016 4:46 pm

MOOG_NOOB wrote:Thanks for the help. Unfortunately work has me bouncing around the country the past few weeks, but hopefully I will get some time to stare at the schematics some more soon. My source has version 3.2 firmware so I'm not sure if 2.0 would run with the hardware configuration (I know there were a few I/O changes, but not sure what else). I've replaced a couple of chips on the digital PCB with no change in performance...I've also run it with the two digital PCB to synth PCB ribbon cables disconnected and the switches still work the same, leading me to believe it's an issue on the digital PCB. That was my suspicion, but little bits are helping me confirm it...now I just need to spend some time with the scope and meter to narrow it down. When I'm done maybe I'll write a book!


How's it working out? If it's a main-board problem then I suspect it's going to be expensive to fix - or impossible to fix.

davebr
Posts: 13
Joined: Sat Jan 18, 2014 5:38 pm

Re: Help! The Source is killing me!!!

Post by davebr » Thu Sep 08, 2016 1:34 am

I just finished repairing a Moog Source although the membrane was in good condition. That synth is full of sockets and connectors, all tin. Tin corrodes and it's been nearly 40 years since it was manufactured. The first thing I would do is re-seat every connector and every IC. Some of the connectors feel quite rough when reinserting so I would use some contact cleaner on the pins to help lubricate them. You can spray on a cotton swap and wipe the pins.

You say you tested the membrane but how? It is a matrix keyboard and there was an earlier comment about removing the conductive surface. That has happened to me before and I have had reasonably good luck with conductive silver paint so be very careful with those connections.

The keyboard is scanned. The data lines are pulled high on the receiver side. The scanning side pulls low through U5 and 6 diodes. I would scope those and make sure every line is being pulled low appropriately.

The receivers are CMOS 4502. I have seen old CMOS go wonky with wrong levels, etc. You should be able to scope the scanning line going low and follow that signal through the matrix keyboard and see the corresponding line go low. Look at it on both sides of the receiver. The output is tri-state so you will have to sync your scope with the read line. Confirm that you can see the key press for all the inoperative keys. If the data is getting to the processor and they keys aren't working, then you have major problems. I would think that you have some logic problem where the inoperative keys are not being scanned.

The Vol of the LS378 is 0.5V. The diode drop is probably around 0.6V so you have a Vil of about 1.1V. The nice thing about the 4502 is Vil is 1.5V so you have margin. Many keyboard scanning designs don't.

Good luck. You can always PM me and we can take this conversation off line if you want more help. I'm not a Source expert but this is a reasonably simple microprocessor design that I am familiar with having designed similar systems in that timeframe.

Dave

Post Reply