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Need help restoring a Maestro
Mr. Lumbergh: I took delivery of a Maestro last week finally after a few months of searching and having at least two get away from me. I'm excited to have one but it does have some problems that I would appreciate your help sorting out. Mr. Kuzmin himself did answer a couple of my questions in the comments section of a demo video on YouTube, but suggested that I come here for help since he didn't have much experience with the troubleshooting and maintenance. Unfortunately some of these problems started only after a couple days of playing it. The trouble I'm having is as follows: When I first start it up, the 32', 8', and 4' settings are active and sound is a bit distorted. Is this normal or should it default back the 32' Keyboard bank (Clavinet) setting at start? The above issue stops if I manually select a stop and I'll have just the 32', 16', etc. The Strings bank only works intermittently and when it does, only the 16' - 2' stops; the 32' doesn't function at all though the LED is lit. The Brass bank outputs only at very low volume, I need to turn the volume up all the way to hear it at all. The Filter Frequency adjustment doesn't have any noticeable effect on any of the banks; Resonance did when I first tried it out but now also isn't working. If I understood the demo video correctly, only the Brass bank is affected by the Filter adjustment so I'm wondering if this is related to the volume issue I'm having with that bank. The Fade (Decay?) setting doesn't have a noticeable effect. The Generator Setting/Master Pitch knob needs to be pulled back to about -1 to get A440 so I'm thinking some components in that circuit might have drifted with age and handling. Aside from that, there are no dead keys and the chorus, vibrato, arp, and trem function as does the memory. I know that's a long list of problems but I bought it knowing it was likely that I'd have to do some work to it and I love the sound so I'm determined to restore it. One other thing to mention, since I'm currently in the US the mains voltage is 120V 60Hz and I know this needs 220V 50Hz. I did get a step-up transformer to take care of the voltage but it isn't advanced enough to also change the frequency. If I'm interpreting the schematic correctly it gets rectified to DC immediately after being stepped down in the power stage and shouldn't affect function but please correct me if I'm wrong. Would it also be advisable to replace all the electrolytic capacitors in the power stage because of age? I found a shop in St. Petersburg that sells MIDI retrofit kits for this on their Ebay store and so will be opening it up to do that work and would like to take care of the maintenance work while I have it on the bench. I appreciate any help or advice you might have to restore this great synth.
Ответов - 12
Muztech: Помогите человеку, кто имеет опыт.
Mr. Lumbergh: I'm not sure I understand your reply. I've overhauled a couple of amplifiers and have built several effects from scratch, but haven't worked on a synth yet. I'm hoping the community can point me in the right direction because at the moment I'm not quite sure where to start.
Mr. Lumbergh: My apologies, rereading your post you're asking for community help. I didn't mean to appear rude with my previous reply.
Gregory: Muztech пишет: кто имеет опытВы не знаете, выдержат ли диоды 60Hz?
Mr. Lumbergh: How would the frequency effect the diodes? 60Hz is still low frequency, could it have drifted since manufacture?
Gregory: Mr. Lumbergh пишет: could it have drifted since manufacture?If you are aware of this, then why are you asking about this?
Mr. Lumbergh: I know that capacitors, especially electrolytic, and carbon-composition resistors are prone to this, I wasn't sure if diodes were the same.
Mr. Lumbergh: Mr Kuzmin, could you please confirm the values of the large filter capacitors in the power stage? The schematic available on this site just shows them as "2200,0" but if it's microfarad that seems high to me; I recently restored a guitar amp and the equivalent caps in that circuit were 47 microfarad 450V. I think at least some of the trouble I'm having may be the old capacitors in the power stage suddenly being power cycled again after spending many years in storage since some of the problems developed over the couple days after I received it.
Gregory: Mr. Lumbergh пишет: The schematic availableI don't know schematics of the Maestro, but I assume that a parametric power supply is used there. In such power supplies, large capacitors are used, but they are designed for low voltage (after the step-down transformer). Judging by the values you specified, a switching power supply is used in the guitar amplifier. Vladimir Logichev told to you about the probable ways of repair.
Muztech: "Mr Kuzmin, could you please confirm the values..." Capacitors are 2000 microfarad (soviet standards) 50Volts and this is normal values for the low voltage power supply. Don't compare with valve amps.
Mr. Lumbergh: I've finally been able to start placing the order for replacement components and I'm finding it difficult to locate 2000uF 50V; is it safe to replace with 2200uF 50V? I'm also not familiar with the naming convention on some of the smaller caps on one of the boards and would like to confirm values please: 10μM 1μM 10μN 1μ0M If I'm not mistaken the M signifies 20% tolerance but Western cap code charts don't list N. I'm also unsure of the significance of the μ being between the digits on the last one.
Gregory: Mr. Lumbergh пишет: is it safe to replace with 2200uF 50V? Yes.
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