Vintage Synth Repair

--- In vintagesynthrepair@yahoogroups.com, Philip <eggwheatis@...> 
wrote:
I found it. Connector P28 was plugged in backwards on the Common 
Analogue board. :o)

Dare I say it's almost 100% fixed??

Just got to tune the filters tomorrow!

Thanks, Phil.


> The problem is when you go into MONO mode, the filter stops 
tracking across the keyboard. The 1/3 and 2/3 KB Tracking buttons in 
the filter section have no effect. It's tracks ok in polyphonic mode.
> Â 
> Also in Poly mode switching the 2/3 KB Tracking button on in the 
filter section makes the third oscillator drop almost one octave 
across all 6 voices.
> 
> So what do you reckon? 
> 
> Thanks< phil.
> 
> 
> Â 
> Â 
> Â 
> 
> 
> --- On Sat, 1/11/08, gerryrdahl <gerryrdahl@...> wrote:
> 
> From: gerryrdahl <gerryrdahl@...>
> Subject: [vintagesynthrepair] Re: Memorymoog repair
> To: vintagesynthrepair@yahoogroups.com
> Date: Saturday, 1 November, 2008, 12:50 PM
> 
> 
> 
> 
> 
> 
> Hi Phil,
> What are the readouts for the Osc's?
> When you press c-7-enter-enter- 1-1, what does the display read?
> If it reads dead osc or LOW, check the others and see what
> you get.
> You may have a CTC osc scanning problem, where the CTC cannot 
> count (or check the tuning) on the osc's.
> 
> Also what version firmware do you have?
> When you do a c-0-enter all the leds blink, in the patch readout
> will be a flashing number, this is the version.
> 
> Also check the pitch bend and fine tune circuit.
> These are supposed to be disabled during autotune. if not
> then the MM will not tune.
> 
> Let us know.
> GD
> 
> --- In vintagesynthrepair@ yahoogroups. com, Philip 
<eggwheatis@ ...> 
> wrote:
> >
> > Hi, i just started back tonight on it.... After a a very 
expensive 
> purchase of  some CEM ic's I have all the voices working on it 
now.
> >  
> > I was seriously scared off putting the new IC's in in case they 
> died again...but I bit the bullet and all seems fine. Phew!
> >  
> > SO now I have a fully working but seriously out of tune 
> Memorymoog. The autotune wont tune it..too far out. I just 
get '0 
> tuned'
> >  
> > I checked the calibration out in the manual and I found it a bit 
> confusing...
> >  
> > Has anyone got any tips on calibrating it? 
> >  
> > Thanks, Phil.
> >  
> > 
> > 
> > --- On Tue, 21/10/08, gerryrdahl <gerryrdahl@ ...> wrote:
> > 
> > From: gerryrdahl <gerryrdahl@ ...>
> > Subject: [vintagesynthrepair ] Re: Memorymoog repair
> > To: vintagesynthrepair@ yahoogroups. com
> > Date: Tuesday, 21 October, 2008, 4:13 AM
> > 
> > 
> > 
> > 
> > 
> > 
> > Hi Phil,
> > How has the Memorymoog turned out?
> > 
> > Did the replacement CEM's and a calibration finish her up?
> > 
> > Would like to know.
> > 
> > Thanks.
> > GD
> > 
> > --- In vintagesynthrepair@ yahoogroups. com, "eggwheatis" 
> > <eggwheatis@ ...> wrote:
> > >
> > > 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.matrixsy nth.com/blog/ media/Moog/ 
MemorymoogSchema 
> tics/
> > > > 
> > > > The service manual is here: 
> > > > http://www.retrosyn th.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
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>