Phew..I fixed the pot problem, well I think I have. I ended up taking every board out and going through them with a fine toothed comb, I cleaned any surplus flux off, checked everything..scoped everything. I just could not find it. Then something occured to me..like many things do when repairing stuff!..on the schematics there is an LF351 op-amp on the output of the DAC..but it the actual socket was a TL071 which should be fine, and i had already swapped it out..anyway it is an equivalent and is even mentioned in parenthesis on the parts sheet next to LF351, as is TL072 as an equivalent for LF353. In fact my memorymoog has TL072'a and TL)71's throughout. Now I know how sensitive digital circuits are to 'equivalents' so I put in an LF351 and bingo....it was fixed! Or so I thought basically I did it again once after playing around with it after an hour..now normally it did it every 30 seconds so it is 99% better and hasn't done it again. Maybe the DAC is faulty itself but I still don't understand how this would effect the displayed pot values. Surely that's down to the A/D? Also with good news comes bad...after fixing that problem I rechecked the voices..I had lost another voice! AFter finding another red hot regulator on a voice board I found all three CEM3340's were shorted!! Arggh!! I was feeling pretty sick considering how expensive they are! I must have shorted something out while trying to fix the pot problem...oh well.. So anyway I've got 5 CEM3340's on the way(one spare), a 3310 and a 3360. After calibration that should be it. Fingers crossed X --- In vintagesynthrepair@yahoogroups.com, "eggwheatis" <eggwheatis@...> wrote: > > Well this (hopefully)last problem is proving to be really difficult > to solve. It wasnt the Zener even though it was bad. It acts as a > regulator for the +10 vdc to the DAC from the Control boards... It > was causing it to sit at 11.5 vdc. Changing it did nothing. > > It's one of those niggling annoying problems that seems to be > undetectable...its driving me nuts..I'll try to explain it better. > > Basically you turn a pot on this synth and the pots value is shown on > the alpha/dec LED display, you turn the second pot the display > instantly shows that pots value..so far so good...but after a few > turns of various pots, it will stick on a value and won't change with > the new pot movements, pressing buttons, turning other pots wont get > rid of it(you can see the correct values flickering behind it)..even > turning it on and off. You have to go back and find the pot thats got > the value 'stuck'. Zero that pot and it's fine again. It's totally > random and depends on the combination of pots and values. The actual > sound itself changes fine with the pot movement. It's just the > displaying of the values that is a bit screwed. > > Remember is the physical displaying of the values that gets stuck, > not the actual values that control the analogue parameters. They are > working fine. > > If anyone can help I'd really appreciate it, the schems are here: > http://www.matrixsynth.com/blog/media/Moog/MemorymoogSchematics/ > > The service manual is here: > http://www.retrosynth.com/docs/memorymoog/mm_service.pdf > > Apart from this fault..it seems to be almost fixed. > > Thanks, Phil. > > > > > > > > > > > --- In vintagesynthrepair@yahoogroups.com, "eggwheatis" > <eggwheatis@> wrote: > > > > A bit more fixed..:o) > > > > well actually diagnosed.. > > > > The reason all the voices were dead on one card was because a > > CEM3340 VCO chip was shorted, this pulled down the 7905 regulator > > that sits on the edge of each voice card killing the supply to the > > other CEM's. I found that a CEM3360 VCA chip was also dead on the > > same card. So after swapping a few CEM's around I know have just > one > > Oscillator 3 down. > > > > After that I noticed the VCF adsr wasnt working on one voice. A > > quick look at the schems revealed it is generated by a CEM3310 on > > the contour generator board. Sure enough I found the 3310 was dead. > > > > So that, on the face of it, appears to be the voices sorted out. Im > > sure I'll find more problems. > > > > The synth is still totally out of tune, so it will need full > > calibration. I'm not going to try that until I have located all the > > CEM chips I need. > > > > I also swapped all the HC ic's out for the correct LS versions and > > anything that isnt specified in the parts list. For instance a lot > > of the op amps are 1458's, the schematics and parts list specify > > 4558. The manual also has an addition saying you should swap any > > found to 4558. The 4558 is apparently superior. > > > > I still have the problem with the displayed pot values, I talked > > about in an earlier post(below). It drove me mad..I checked out the > > whole of the POTPOS circuit, the MUX circuit..the display > > circuits....eventually after forgetting theory, schematics and just > > randomly testing things, I found CR1 to be open on the DMUX board! > > It's a 6.2 Zener..I avent changed it yet as I was going out..but > > after checking the schems I reckon I might have solved it..it's not > > mentioned in the service manual, and it's right on the edge of the > > schems.. > > > > Thats it for now..Phil. > > > > > > > > > > > > > > > > > > --- In vintagesynthrepair@yahoogroups.com, "eggwheatis" > > <eggwheatis@> wrote: > > > > > > Fixed the hopeless switch matrix :o) there was a ribbon cable > > plugged > > > in the wrong way round into the common analogue board! Large > > repairer > > > error #5..... > > > > > > So now all the button functions work properly and I have > > Oscillator 3 > > > back!... although only 4 voices working. > > > > > > I also changed 4 of the hc138's to LS138's and the filter has now > > > started tracking the keyboard properly...I discovered two HC377's > > on > > > the digital board too..they should be LS variants again... > > > > > > So basically im left with OSC 1,2 and 3 not working on the same > > voice > > > card(3 dead cem3340's on the same card surely not? I hope) OSC 3 > > dead > > > on one other card. Hopeless autotune '0 tuned' all out of tune > > with > > > each other even on the same cards... > > > > > > Oh and the weird pot problem: when you > > > move the pots the numbers in the alpha display move up and down > > which > > > is correct, however say you turn one pot and move to another, > > > well the first pots status doesn't clear from the display, it's > > > stuck there, you can see it flicker as you move the other pot but > > > it's stuck there unless you go back and zero the original pot. > > Only > > > a few pots seem to cause this problem. > > > > > > I reckon swapping out those wrong HC ic's will cure that..maybe.. > > > > > > Im sure I'll find more problems too. It's amazing how 'previous > > > repairer error' can completely disable a synth that probably only > > had > > > a couple of faults to start with. > > > > > > Getting there... > > > > > > > > > > > > --- In vintagesynthrepair@yahoogroups.com, "eggwheatis" > > > <eggwheatis@> wrote: > > > > > > > > Well ive now got sound out of it :o) this is going to be fun > > > > though...yet again someones been in this before me that looks > > like > > > > they weren't on the ball. All the IC are in sockets...but most > > of > > > > them have been replaced sometimes with the wrong variant. > > > > > > > > No sound was indeed caused by the PSU....an electrolytic > > capacitor > > > in > > > > the +15 circuit on the DMUX board was put in backwards. > Repairer > > > > error #1. > > > > > > > > I thought I'd start by fixing the LED's on the left hand control > > > (LHC) > > > > board and the missing digit in the alpha display so I could see > > > what > > > > was going on better... > > > > > > > > The dead/stuck on LED's were caused by one of the legs of the > > ls378 > > > > at U8 on the LHC board being bent under itself in the socket. > > > > Repairer error #2. > > > > > > > > The dead digit in the alpha display was caused by a dead output > > on > > > > the LS273 at U1 on the LHC board. > > > > > > > > Anyway so now I can see and hear whats going on I have a whole > > host > > > > of new problems :o) > > > > > > > > I have no Oscillator 3 at all across the board, Osc 1 and 2 > also > > > dont > > > > work on one voice. None of the oscillators will auto-tune, i > get > > > > the '0 tuned message'. The filter self oscillates but wont > track > > > the > > > > keyboard. > > > > > > > > The switch matrix is hopeless on the LHC board, buttons > activate > > > > wrong functions basically, the appegiator doesnt work nor does > > the > > > > hold function... > > > > > > > > Things I can see right off the bat but need to get spares to > fix > > > are: > > > > All the 74ls138's on the digital board have been replaced with > > HC > > > > Cmos variants...not a good idea, these are not compatible with > > TTL > > > in > > > > most cases, so i would think they are causing a lot of problems > > > > (fingers crossed). You need LS in there or HCT at least.. > > Repairer > > > > Error #3 > > > > > > > > Also there is a TL071 missing out of a socket on the DMUX > > > board..this > > > > is connected to the auto tune circuit..buffers one of the > > outputs I > > > > think. Repairer Error #4 > > > > > > > > All in all a lot of fun! > > > > > > > > Phil. > > > > > > > > > > > > > > > > > > > > --- In vintagesynthrepair@yahoogroups.com, Philip <eggwheatis@> > > > > wrote: > > > > > > > > > > I just got a broken Memorymoog. It's really clean, near mint > > in > > > > fact, but not working. Half the reason I bought it is because I > > > like > > > > a challenge :o) ..I haven't even opened it up yet so I thought > > I'd > > > > post up the problems to see if anyone has an idea. > > > > >  > > > > > It boots up ok, but makes very little sound the most you get > > out > > > of > > > > it is a thump or slight squeak when you hit a key, the same > > pitch > > > > wherever you hit. The digital side seem to be mostly working. > > > > >  > > > > > If you hit autotune it comes back with '0 tuned' so it can't > > tune > > > > any of the oscillators probably because it cant 'hear' them so > > to > > > > speak. > > > > >  > > > > > First thoughts are some kind of DAC problem. > > > > >  > > > > > 2: All the LED's on the left hand side don't work at all but > > the > > > > buttons do. A few are just stuck on all the time, again the > > buttons > > > > work. > > > > >  > > > > > 3: one digit on the alpha/numeric display is barely visible. > > > > >  > > > > > 4: this is a slightly weird one which is hard to describe, > > when > > > you > > > > move the pots the numbers in the alpha display move up and down > > > which > > > > is correct., however say you turn one pot and move to another, > > > > well the first pots status doesn't clear from the display, > it's > > > > stuck there, you can see it flicker as you move the other pot > > but > > > > it's stuck there unless you go back and zero the original pot. > > > Only > > > > a few pots seem to cause this problem. > > > > >  > > > > > Any ideas would be helpful. Obviously the first thing im > going > > to > > > > check is the PSU when I open it up later. > > > > >  > > > > > Thanks, Phil. > > > > >  > > > > > > > > > > Send instant messages to your online friends > > > > http://uk.messenger.yahoo.com > > > > > > > > > > > > > > >
Message
Re: Memorymoog repair
2008-09-03 by eggwheatis