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Amcrons - Dilemma
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ceharden View Drop Down
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Joined: 05 June 2005
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Points: 11748 		Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 22 November 2023 at 11:48pm
Can't offer any good advice I'm afraid, haven't worked on a Macrotech for a long time and always found them a bit of a tricky customer.  Mainly because the grounded bridge topology means that it's sometimes hard to know what to use as a reference because 'ground' moves in the opposite direction to the output.  When you're chasing offsets, it can be hard to know which side of the bridge the fault is on.

Have you got one good channel and one faulty one?  If so, have you tried swapping parts between the two to see if the fault follows rather than doing a blanket replacement?
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ChrisWard View Drop Down
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Points: 37 		Post Options Post Options   Thanks (0) Thanks(0)   Quote ChrisWard Quote  Post ReplyReply Direct Link To This Post Posted: 23 November 2023 at 8:36am
Originally posted by shaun1264 shaun1264 wrote:

If you going for replace the drivers and outputs.  They have to be matched VBE and Hfe 
Yes thank you, do you know the range or tolerance they should be Matched
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Points: 37 		Post Options Post Options   Thanks (0) Thanks(0)   Quote ChrisWard Quote  Post ReplyReply Direct Link To This Post Posted: 23 November 2023 at 8:40am
I think its the Output Board.....as I have checked and replaced obvious culprits on the main board...but when i pull the pre-drivers out I can validate 
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ChrisWard View Drop Down
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Points: 37 		Post Options Post Options   Thanks (0) Thanks(0)   Quote ChrisWard Quote  Post ReplyReply Direct Link To This Post Posted: 23 November 2023 at 8:48am
I have a good side, and I've been using that as a reference, I also have another 601 that has a bad channel, but I also have 3 others (601, 1201, 2401) so I don't mind having spares as some components seem to be going obsolete.

I pulled the Output Resistors off to allow the DC Fault protect to keep the power on for longer, before it was cycling on/off and it was hard to get any readings...it seems to be the high side that is causing the problem.

The 601's are used in the high to top range in a so they have only ever had >1khz loads at 16 ohms  for their entire life..
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ChrisWard View Drop Down
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Points: 37 		Post Options Post Options   Thanks (0) Thanks(0)   Quote ChrisWard Quote  Post ReplyReply Direct Link To This Post Posted: 29 November 2023 at 7:58am
Hi Guys.....so good news last night I found the main issue, it was a broken PCB track in the Voltage Translator section on the Main board...I was checking every component after reading some guy had wasted hours on a shorted cap....

I had also replaced 4 x 1N4148, the track was right next to a solder pad so even zooming in with a camera you can only just see it....I found it by tracking the Ch1 feedback route to the Voltage Translator with a DVM

It's producing a good output on the scope now, I still have a bright IOC led that needs resolving....

Good news is that I'm pretty clear on the function of most of this amp now, having studied the schematic for so long, also learnt some ways to isolate and bypass's functions, which is going to help me with amp no 2 another 601



Edited by ChrisWard - 29 November 2023 at 8:16am
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ChrisWard View Drop Down
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Points: 37 		Post Options Post Options   Thanks (0) Thanks(0)   Quote ChrisWard Quote  Post ReplyReply Direct Link To This Post Posted: 30 November 2023 at 7:22am
Sorted the IOC issue being on constantly....this was C501 on the display board small 0.47 cap in the comparator feedback loop, its strange as it measured fine but clearly defective
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