Midiverb ii issues?

Supply rails all correct voltages and clean (check with digital voltmeter and 'scope) ? Processor chip receiving correct reset ? Processor clock running ? No user control jammed in 'operating' position ? Such things can cause a processor to 'loop forever' if it executes a bit of code during boot up, to check for button presses that are part of a diagnostic entry sequence, and the button that's being 'pressed' is not one that is being expected.

Arfa

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All indicators lit but no numeric display? No processor bootstrap.

I have a couple of those BTW. Nice units for sound reinforcement.

Thanks for your help Meat Plow,

Any ideas what could casue the processor to not boot? Could this be a voltage issue maybe??

Tanks for your help!

Thanks Arfa-

My next plan is to check the voltages. Without the schematic, I'm a bit fuzzy on where to check the voltages and what they should be.

Do you have a method to track down the correct voltages??

Thanks again for your help!

oot

If I had some service literature on it I might be able to point out a few possibilities. The area of interest Arfa posted are what I would start with but without being able to identify those areas and their signals you're flying blind. You might try a little research on a factory reset. Maybe Google 'midiverb II no boot' and see what pops up.

You might pay particular attention to Arfa's suggestion of the uP receiving the correct reset.

The first thing I used to do with these old style microprocessor things, after checking the power supplies, was to force a warm boot by taking the reset line low or high - whatever is appropriate to force a reset. (get the datasheet for the processor to find what is required and where) It was surprising how many then suddenly burst into life.

Gareth.

I have a Midiverb II, Microverb III, and some other Alesis boxes. I've had to go inside to fix every one at various times. The big 1000uf and 2200uf filter caps are all junk in most Alesis boxes. If you have an oscilloscope, you'll see lots of ripple on the power supply buses. There are also 0.1uf decoupling caps, which like to short out.

No display sounds like no power. Even a comatose processor should show some lit segments on the display. I agree with Arfa's approach. Follow the power.

Note that the wall wart might be 9V AC or 9V DC. Alesis used both with identical connectors. An AC box will actually run with a DC power supply, but will also do strange things. Checking the Alesis web pile, it's a 9V 830mA AC P3X110 adapter.

If you have problems working on it with zero information, these sites might be useful:

Yes, good advice. A forced reset is a good test. However, the OP's experience of dealing with this sort of problem appears limited, so if I were he, I think I would definitely be looking for some schematics, as without them, it's going to be difficult for him to troubleshoot this ...

Arfa

Yes, good advice. A forced reset is a good test. However, the OP's experience of dealing with this sort of problem appears limited, so if I were he, I think I would definitely be looking for some schematics, as without them, it's going to be difficult for him to troubleshoot this ...

Arfa

If you get the datasheets for the uP and ROM/RAM chips, you can scope each data and address line and sometimes come across one that just doesn't look right, e.g. it has values that are not 0 or 5 volts, but something in between. Forcing a reset can sometimes help by providing a few cycles of program to watch before the unit hangs.

Cut bus tracks til you find out which chip is fouling the line.

I have managed to fix quite a few units this way where the schematics were not available.

(By the way, I'd always change the program RAM chip first if feasible, as these used to be the most likely chip to fail)

Gareth.

Thank you everyone for your help!

I will try to work out some of the issues tomorrow at the shop.

Also, if a filter cap tests good using a ESR meter, could it still be bad??

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A shorted cap will check good with an ESR meter. You should do a sanity check on what it is telling you.

tm

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If there is a doubt, sub it. As far as I'm concerned if it passed the ESR test it's good (for the time being)

Well, it could be shorted. Somewhat rare for electrolytics IME, though.

In the past, I have seen many electrolytics that were serving as rail decouplers, that have gone short. The little purple 10uF's that Panasonic used to litter everything that they built with, were favourites for failing short. As you say, doesn't seem to be as common an occurrence these days as it once was, though. Interestingly, I had a s/c electrolytic just today (see my post regarding some Restek speakers). It was one of those brown plastic 'Siemens' types that you used to see a lot of in Grundigs and B&O's.

Arfa

It was very rare with American built electronics. Most failures were open filter capacitors, or damaged 160 mF, 250 V 'Low Power Factor' electrolytics used in the voltage doubler power supplies. BTW, 'Low Power Factor' were rated in the ripple current they could handle. Today, they would be a Low ESR rating.

The only shorted electrolytics I remember in American built electronics was the low voltage caps used in the cathode circuits of audio amps.

Interesting. I wonder why the difference ? A few years back - say 10 or so - I would have said that I saw as many short circuit electrolytics, as any other problems with them such as open circuit, low value, leaking, bulging etc. Now though, short circuit is comparatively rare. As to cathode caps, I think that I have probably seen more that were open circuit than short. Used to be a big problem in the frame output and audio output stages of TV sets, back in the day ...

Arfa

Sprague had high standards, but you paid for it. Japanese crap hit the US hard in the early '70s and you saw a lot more failed electrolytics. Sprague started shutting down their plants as demand for high quality electrolytics dropped. I still have a roll of aluminized mylar from the Orlando plant, along with a partial roll of 'component lead' they used on their famous 'Orange Drop' capacitors.