New sockets fixed some problems. One socket even had two legs broken. The biggest problem now is the ADSR and other controls for the poly synth section. Can you tell me if it's safe to connect a 5V signal directly to the input controlling attack on the CEM ADSR chip and also to the input controlling resonance amount on the CEM filter chip? The resonance level is now fluctuating a lot, so it's seems like either the filter chip is getting a fluctuating signal or the filter chip has a problem. Same goes for the ADSR chip. Greatful for any advice!
---In vintagesynthrepair@yahoogroups.com, <wmc_mick@...> wrote:
I found a broken trace (at a connector) that stopped the sutain-signal arriving at the CEM3310. The brake was impossible to see, even with a magnifying glass. I also managed to fix the problem with the attack-signal. The socket for the CEM3310 was bad and I replaced it. ALL chips on this synth are socketed and it seems the sockets are not so good anymore, I suspect the remaining problems are likely due to bad sockets also.
Maybe if somebody with more experience would have seen the synth they had instantly suspected the sockets, but now I now, I just also read tips about repairing arcade machines and there they said that edge connectors and ic sockets are one of the most common causes for failures.
I will update my progress later in hope that it helps somebody else.
Maybe if somebody with more experience would have seen the synth they had instantly suspected the sockets, but now I now, I just also read tips about repairing arcade machines and there they said that edge connectors and ic sockets are one of the most common causes for failures.
I will update my progress later in hope that it helps somebody else.
--- In vintagesynthrepair@yahoogroups.com, "Mikael" <wmc_mick@...> wrote:
>
> Hi again!
>
> I have now replaced all the electrolytics in the Crumar Composer. I also cleaned the pots and replaced an MC1741C op-amp in the end stage. The main output is now working. :) Quite a few of the electrolytics had leaked so I guess it was good to replace them all.
>
> The sound of the mono-synth, organ and string section is now clean. Some problems remain, mainly the envelope on the poly-synth section. The envelope and filter of the poly-synth is controlled by the same pots as the mono-synth, so it's possible to use the pots for one section at a time. The envelope and filter work great for the mono-section.
>
> Problems with the poly-section:
> - Attack at lowest is slow, and seems to vary betwwen 1 second and 10 seconds (maybe due to warm up or something).
> - At the start of a note, there is sometimes a "pop"-sound and always when I release the key or when the attack has reached maximum (then sound stops).
> - Sustain level is always zero (the sustain pot has no effect).
> - The decay setting works sometimes and the release seem to work normally.
> - The filter cutoff is always quite high, I can change it with the pot but the lowest cutoff frequency is still quite high.
>
> I have uploaded a photo of the poly-synth board to help troubleshooting. Maybe some of you can spot components that are likely to fail etc.
>
> https://dl.dropboxusercontent.com/u/26435295/crumar_p-975.jpg
>
> The envelope is controlled by a CEM3310, and the filter is a CEM3320 and the VCA is a CEM3330. The mono synth is controlled by another set of the same CEM chips. There are trimmers by the CEM chips for calibrating, but I have no idea which trimmer does what. I guess I could replace the CEM chips from the mono-section but I'm afraid there is some other problem that could do damage to those chips. Anybody have any of these CEM-chips for sale btw?
>
> About the op-amps (MC1741 and MC1458). Can I replace the MC1458s with low noise alternatives like NE5532?
>
> As always, I'm greatful for any help!
>
> As a sidenote, I bought a proper desoldering gun. Using that the recapping was a walk in the park, a long walk but.. I feel it was worth buying the desoldering gun only for this job. :)
>
>
> --- In vintagesynthrepair@yahoogroups.com, "Mikael" <wmc_mick@> wrote:
> >
> > Hi all!
> >
> > I bought a rare Crumar Composer I while ago but it has some problems. This synth has a mono synth section, a poly synth section, a organ section and a string section. All these sections can be combined. There is a separate output for every section and a main output. The separate outputs work but the volume for the main output and the main output itself do not work, could this be a problem in an amp-sircuit or something?
> >
> > The problem I'm trying to look at now and ask about is an issue with the poly synth section. The problem is that the attack for the envelope is VERY slow, I can change the attack rate on the front panel pot but the fastest attack is about 15 seconds. Can anybody give me a hint where to look for the problem? Also there is a pop when I release the key on all keys it seems. The envelope of the poly-synth section is generated by a CEM3310 chip. There are also CEM3320 and 3330 chips on the poly section.
> >
> > Last problem I'm having is that the release rate for the organ section is very sensitive, it seems that the effective range is about 30 degrees (1-1.5 on a scale from 1-10), if I turn the pot about 40 degrees I have a VERY long release time.
> >
> > I would really like to get this synth in shape, it sounds so good and it's very rare, I think Crumar made only 500 of these.
> >
> > Thanks in advance!
> >
>
