After the Groovebox repair went so well and now my bench is clear, I thought it might be time to look at the big fella again.I have an old Yamaha CS20m mono synth, one of these guys:It was working when I moved overseas and non-working when I came back. It has previously had all its electrolytic caps replaced. It has been sitting in the garage non-functional for about ten years now.Hopefully I've learned a bit in those ten years and may be able to get it working again. Or at least make some progress, hey. In the meantime, the internet has also delivered the goods in the form of a complete service manual and helpful videos like this one:phpBB [media]Nice work, internet. Look at those delicious circuit boards. It's practically begging to be repaired.Compared to the Groovebox, which was a total pain in the arse to get into, these guys have gone out of their way to make everything accessible. It's all on hinges! All the sections are divided off onto their own boards, the boards are all single-sided and it's all big, chunky old components. Even a meat-fingered bass player should have a reasonable chance of repairing this thing.I think I'm gonna need an oscilloscope for this though. So my first question is, what's the sweet spot for somebody who doesn't really want to spend any money but also doesn't want to buy a useless heap of crap? Let's say I had to choose one of these: http://www.trademe.co.nz/Browse/SearchR ... dCategory=

First things first - power lines seem to be nice and strong except whoops, the -10v rail is dead. Turns out that one of the fuses in the power supply had blown. Notwithstanding the reason why that might have happened, after replacing the fuse the power supply seems to be all good.After reconnecting and powering up, there is no sound, the panel lights are all off and the panel apparently unresponsive. The LFO trigger light is on, but not blinking and not responding to the speed knob. So it looks even more dead than the one in the video. Checking the CPU seems like the next thing to do but I guess I need to find a scope in order to make any progress there.

I don't think I can afford to be that picky. If you follow that link you'll see there's about 15 oscilloscopes currently for sale in the whole country. A few Tektronix ones, although none of the models you mention.Is a 10mhz or 20mhz scope too rubbish? Is it possible to get something worthwhile for $150? If I have to spend a thousand bucks this project is going to come to a halt pretty quickly.

As far as scopes, I'm not an expert by any means, but I recently got a Tek 465M. Same as the 465 (but not the 465B, I believe), but different enclosure. The nice thing about it is that it doesn't have a fan that I ever need to clean, or that will ever get noisy. It's capable of viewing signals up to 100MHz, which is more than you'll need.When I was reading about this stuff (and asked here), the 22xx series was recommended. There's also a Yahoo Tektronix group in case you want nuts. That list is insane, like a billion emails a day from people fixing and collecting old scopes.

kthx kxbxFrom what I can ascertain the Rigol 1054z looks to be closer to $1000 in our money when purchased over here I really don't have that kind of money to drop on hobby stuff right now (if ever) but it's given me something to consider. If an old 2 channel 10MHz analogue scope *THAT WORKS* will suffice, I might see if I can get something like that cheap enough, and if and when I find myself wanting to do more it will be a sign that it will be money well spent I guess.

A 10 MHz scope that works will cover nearly every analog synth repair. Two channels is probably the minimum, otherwise you can't look at input and output signals sync'd in time.I have a Rigol 1054z DSO, if you have $400 that will cover a whole other range of repairs and is usually nicer to use in general. It can also be modified for 100MHz BW and deeper memory for no cost.

Anthony Flack wrote:kthx kxbxFrom what I can ascertain the Rigol 1054z looks to be closer to $1000 in our money when purchased over here these guys look like the AUS/NZ dealer, looks like things are pricier over there. http://www.emona.com.au/products/electr ... 1054z.htmlAs for bandwidth, if you have no interest in radio or modern digital systems you probably don't need high bandwidth. The highest bandwidth signals I look at in audio gear are clocks and comms stuff in pedals from the 2000s onwards, you will want 50-100MHz bandwidth for those.Try and get something with probes included, but the cheap shitty Chinese ones from eBay will work fine for what you want.

Hm, not quite a thousand bucks but still $665 inc GST (or $694 if that's australian dollars) plus shipping, which is money I don't have right now but I will consider for the future while I look for something cheap in the meantime. Thanks again kxbx.looks like things are pricier over there. Everything always is. We have high prices and low wages so our spending power is a bit shitty in general.

BLAWA guy was selling this locally for $100. An old scope to repair an old keyboard... it's possible that they were even made in the same year (~1980). It's funny to think how far technology has advanced just within my lifetime. Well, I guess it hasn't really been all that long since mains electricity even became a thing.It is very beautiful and even if I do end up upgrading to a modern digital scope at some later date, I will always appreciate it for its lovely vector display and I will definitely be trying to get it to play Asteroids.

Did I say the power supply was all right? Not really. I went to check the power lines on the PGM (CPU) board, only to find the -10v line was dead again. Yup, the fuse was blown again. I disconnected all the boards from the power supply board, replaced the fuse and fired up the power supply on its own. The fuse melted right away. Further investigation of the power supply board revealed a tantalum bypass capacitor on the -10v output which had failed and was shorting the line out. I replaced it, as well as its buddies on the other lines for good measure, and fired up the power supply again. Nice smooth DC power was once again flowing.Plugged in the boards again, turned it on and, yup, the fuse blew again. Replaced the fuse and started adding each board one at a time until I found the problem. The line that is blowing the fuse is the one that powers the MOD and FA boards - filters and waveshaping. I take those boards out for now and start it up again. It's not going to make any sound with those boards missing, but I should be able to check the CPU now.Power is stable and not blowing fuses. And now there are signs of life on the front panel!The LFO trigger light is pulsing, and responds to the LFO speed knob. It looks like the oscillators have come on, yay. The panel lights from the CPU are lighting up as well, but they're flashing nonsense and the buttons are not responsive. Something is likely not right on the CPU board.Using the oscilloscope I successfully verify that the clock is delivering a 100kHz square wave as it should, and the reset pin is doing its thing correctly, which was very gratifying. I like having an oscilloscope.I think I will do what the man in the video suggests, assume the main CPU chip is all good because I'm pretty fucked if it isn't, and replace all the cheap generic logic chips on the CPU board which are a more likely cause of scrambled brains. And with any luck the panel buttons may come to life.