Midiverb ii issues?
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From: Gareth Magennis on 26 Jul 2010 15:10 "Arfa Daily" <arfa.daily(a)ntlworld.com> wrote in message news:7N43o.336958$m87.69552(a)hurricane... > > > "Gareth Magennis" <sound.service(a)btconnect.com> wrote in message > news:y1%2o.220782$U%7.143992(a)hurricane... >> >> >> "Arfa Daily" <arfa.daily(a)ntlworld.com> wrote in message >> news:Efj2o.333105$NW.10213(a)hurricane... >>> >>> >>> "El Grillo" <nradina(a)gmail.com> wrote in message >>> news:0b3f8d3e-ce83-4a8d-a032-59a743522db2(a)k19g2000yqc.googlegroups.com... >>>> Hello, >>>> >>>> I'm an new electronic technician TRYING to grasp a hold of my >>>> troubleshooting skills. >>>> I have two Midiverb 2's on my bench currently. >>>> >>>> One I was able to repair by replaceing some bad Filter caps, but the >>>> other is still giving me all the indicator diodes are lit and the 2 >>>> digit screen is dead. >>>> >>>> I tested all caps with an ESR meter and all is good. >>>> Noticed one small decoupling cap looked funky and replaced, but no >>>> luck. >>>> (I'm also a bit unsure if I replaced with the right cap. I had a few >>>> 104 film caps in the shop). >>>> >>>> SO...I'm asking for a bit of help from you all, if willing. >>>> >>>> Any idea where I should be looking? >>>> >>>> Thanks in advice for any help you can send my way. >>>> >>>> nicholas >>> >>> 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 >> >> >> 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. > > 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.
From: El Grillo on 26 Jul 2010 16:35 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?? n On Jul 26, 3:10 pm, "Gareth Magennis" <sound.serv...(a)btconnect.com> wrote: > "Arfa Daily" <arfa.da...(a)ntlworld.com> wrote in message > > news:7N43o.336958$m87.69552(a)hurricane... > > > > > > > > > "Gareth Magennis" <sound.serv...(a)btconnect.com> wrote in message > >news:y1%2o.220782$U%7.143992(a)hurricane... > > >> "Arfa Daily" <arfa.da...(a)ntlworld.com> wrote in message > >>news:Efj2o.333105$NW.10213(a)hurricane... > > >>> "El Grillo" <nrad...(a)gmail.com> wrote in message > >>>news:0b3f8d3e-ce83-4a8d-a032-59a743522db2(a)k19g2000yqc.googlegroups.com.... > >>>> Hello, > > >>>> I'm an new electronic technician TRYING to grasp a hold of my > >>>> troubleshooting skills. > >>>> I have twoMidiverb2's on my bench currently. > > >>>> One I was able to repair by replaceing some bad Filter caps, but the > >>>> other is still giving me all the indicator diodes are lit and the 2 > >>>> digit screen is dead. > > >>>> I tested all caps with an ESR meter and all is good. > >>>> Noticed one small decoupling cap looked funky and replaced, but no > >>>> luck. > >>>> (I'm also a bit unsure if I replaced with the right cap. I had a few > >>>> 104 film caps in the shop). > > >>>> SO...I'm asking for a bit of help from you all, if willing. > > >>>> Any idea where I should be looking? > > >>>> Thanks in advice for any help you can send my way. > > >>>> nicholas > > >>> 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 > > >> 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. > > > 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.
From: tm on 26 Jul 2010 16:51 "El Grillo" <nradina(a)gmail.com> wrote in message news:605a276d-e7c1-42c6-90dd-f65c680acc0b(a)i21g2000yql.googlegroups.com... ..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?? .. ..n A shorted cap will check good with an ESR meter. You should do a sanity check on what it is telling you. tm --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: Meat Plow on 27 Jul 2010 08:52 On Mon, 26 Jul 2010 13:35:24 -0700, El Grillo wrote: > 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?? 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)
From: JW on 28 Jul 2010 06:35
On Tue, 27 Jul 2010 12:52:09 +0000 (UTC) Meat Plow <mhywatt(a)yahoo.com> wrote in Message id: <pan.2010.07.27.12.52.02(a)hahahahahahahah.nutz>: >On Mon, 26 Jul 2010 13:35:24 -0700, El Grillo wrote: > >> 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?? > >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. |