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Old 11th June 2013, 03:30 AM   #21
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Originally Posted by still4given View Post
...... I was typing up a new chart. Now I have to start over becaaus a few of the voltages changed......Fun Stuff!
I like things a bit easier to follow so I just print a few oversize schematics out and pencil voltage readings directly onto a copy and use a pen to mark what is specified, then give the sheet a date or other reference so I know where I am or was yesterday etc. If you want to post it, you can still scan the image and likely get more help because the info. is in one easy look.
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Old 11th June 2013, 03:38 AM   #22
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Yeah, I can put it on a schematic I have been writing them on the parts layout and then using the schematic to check it. Unfortunately, there is nothing specified. If I had a working unit, I could at least compare voltages but I am just shooting in the dark right now. I know I still have something wrong because I am getting 1.6V over the 100ohm resistors I have in place of the fuses and according to Leach, I should be seeing less than 1/2 a volt. Plus the fact that both boards are not reading the same.

I'll do a Schematic with voltages and post it. maybe that will help someone help me.
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Old 11th June 2013, 05:18 AM   #23
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It's just a generalisation but 'divide and conquer' is the strategy for isolating problems.

R32 and 33 control current to the front end and if you see most of the 1.6 volts drop (or rather 16 mA) also flowing through these, you know where to focus your attention. Actually, in an amp this big, 16 mA is not far off correct and I would suspect that "half volt drop" figure, which implies only a tiny 5mV current to the input and VAS stages - even if they hogged all that current.

I realise some of the amplifier has actually been disabled by removing parts but I assume the front end is intact so that feedback is working and DC readings are sensible, otherwise the test regimen is a waste of time.
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Old 11th June 2013, 05:39 AM   #24
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Dr Leach suggested to test the boards prior to attaching the outputs. Probably not a bad idea since I obviously have something wrong because my two boards don't agree. I just wish he had given some voltage specs so I had something too go by. I don't understand electronic circuitry well enough to know where the different voltages originate. I'm hoping someone who does will be able to look at what I have and give some suggestions as to where to look. I will post some schematics tomorrow with my results. Hopefully my scope probes will arrive soon so I can post some results from that as well.

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Old 11th June 2013, 06:48 AM   #25
dangus is offline dangus  Canada
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I'm surprised there isn't a schematic available with typical voltages marked on it.

I can't offer any specific help, but with one amp that gave me trouble, when I returned to it with fresh eyes (and more learning), I discovered that I'd made inappropriate substitutions, and put a couple of transistors in wrong.

I have encountered a number of PC boards which had shorts between traces or cracks in traces that were so small I needed a magnifier to see them, and, quite a few plated-through holes that weren't. There's been the occasional component which had leads which solder just didn't stick to. An adjustable desk lamp and magnifying glasses are helpful; backlighting a board helps with spotting cracked or shorted traces.
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Old 11th June 2013, 07:01 AM   #26
AJT is offline AJT  Philippines
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Quote:
Originally Posted by still4given View Post
Dr Leach suggested to test the boards prior to attaching the outputs. Probably not a bad idea since I obviously have something wrong because my two boards don't agree. I just wish he had given some voltage specs so I had something too go by. I don't understand electronic circuitry well enough to know where the different voltages originate. I'm hoping someone who does will be able to look at what I have and give some suggestions as to where to look. I will post some schematics tomorrow with my results. Hopefully my scope probes will arrive soon so I can post some results from that as well.

Blessings
yes, but it doesn't mean his method is the only way there is to set up his amps...

if you understand how his circuit works, then you will know more or less what the voltages are supposed to be at various nodes in the diagram....then knowing that you can check accordingly...

i know of one builder building the 5 pairs lo-tim who was able to make it work from first power up....i hope he chimes in...

this amp can work from first turn on only and only if there were no mistakes in wiring up and board stuffing....

so check and double check for mistakes, be deliberate and do not be in a hurry, it will be better if someone with fresh eyes can sit with and look at your work....
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Old 11th June 2013, 07:02 AM   #27
AJT is offline AJT  Philippines
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I'm surprised there isn't a schematic available with typical voltages marked on it.
i remember someone posted that drawing here some years back...
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Old 11th June 2013, 07:06 AM   #28
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Yeah, these are home brew boards. It is possible that I have missed something but I just went over the whole board and checked for continuity. Look good but I could have missed something.

I have already found some things I missed before I put it way a few years ago. Back then I was anxious to get onto the next project. This is my project right now so I am determined to get it working. Please stick around. You may see something no one else does.
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Old 11th June 2013, 09:32 AM   #29
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Start fresh, keep all your earlier papers aside. Take the parts list and check all the resistors for their value using a DMM. Tick mark it on the list.

When I am assembling a board, I gather all the required parts and then assemble. This is needed for the resistors especially, as you will not miss the values and any mistake will show up when you find that the remaining resistors are of incorrect value. You can then find out your error and correct it.

Never have all your resistors' assortment at hand and assemble. Mistakes will be difficult to locate.

Gajanan Phadte
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Old 11th June 2013, 09:49 AM   #30
mcd99uk is offline mcd99uk  United Kingdom
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Lt spice could be useful. Make up a superamp schematic and get it working. Then you would have simulated voltages as a reference.

You could take a printed schematic and use a marker to double check everything is correct including continuity of pcb connections.
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