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Old 14th December 2013, 04:03 AM   #1
daly2k is offline daly2k  United States
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Default Meter repair for Pass Amps

Pass Nation, I have some XA100 amps which I really enjoy and cannot part with even for a repair. The issue I have is the meters have quit working properly. The amps are working perfectly and sound fantastic. I have talked to Kent at the Pass Lab site about what to do. Clean out any spider webs and de static the meters etc. This has not worked. Has anyone ever repaired these meters? What did you do? I can easily get them out to clean them more but before I do that has anyone else had this problem? I will not ship the amps to the factory do to the cost and not being able to use them. The problem seems to be that the indicator wand gets stuck halfway up the meter. It should stop at the half way point 12 pm but stops at about 9 am on the meter. I also have a pass x350.5 that has the same problem. I don't want to spray and oil etc into the wand. Kent did send me some voltage readings to take but I haven't done that yet. I think it is a mechanical issue. Please advise if you can and thanks, dave
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Old 14th December 2013, 09:50 AM   #2
Zen Mod is online now Zen Mod  Serbia
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first make measurement

in case of mechanical cause (if , then temperature cycling only can be possible culprit) , you'll not need any sort of oiling

just partial disassemble and some dusting , eventually slight tweaking of pivot setting screw
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Old 14th December 2013, 02:58 PM   #3
daly2k is offline daly2k  United States
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Ok-I will try this, Once I start up the amps I hate to turn them off. I built the Pass 1.2 amps many years ago and have built the Pass A-75 and they are all still working. My meters for them were voltage meters reading the power supply. Thanks again-dave
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Old 14th December 2013, 03:10 PM   #4
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meters in PL amps are usually placed across part of power rail (conductor), measuring tiny voltage sag

whatever , as with any Weston all you need to know is there voltage at connectors
that , and simple probe with ohmmeter ( it must jump , more or less - depending which range on DVM you chose ) will tell where is culprit - even without opening it

if needed , you can bring it to diode DVM test , where you usually push 1mA through DUT
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Old 15th December 2013, 01:18 AM   #5
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Quote:
Originally Posted by Zen Mod View Post
meters in PL amps are usually placed across part of power rail (conductor), measuring tiny voltage sag
Very interesting, ZM. I've never experienced a "real" Pass amp in person, and I assumed the meters measured output watts, or MOSFET currents.

So what you're saying--they effectively are "millivolt meters" tied to two points on one of the voltage rails, and thereby measure the voltage drop caused by the PSU current flowing through the (very small) resistance of a length of the V+ or V- rail itself?

Again, interesting....... would this not indirectly then be a measure of the MOSFET current? Thanks--just curious.......
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Old 15th December 2013, 02:44 AM   #6
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The meter problem is probably mechanical, and if so is likely the wand rubbing
against the front or rear surface. The mechanism is barrel shaped and it is
possible to very gently adjust it forward or backward so as to clear these
surfaces.

I don't need to mention that the amp must be disconnected from the AC
power line when the top is off.

Lacking that, they will have to some back.

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Old 15th December 2013, 04:35 AM   #7
daly2k is offline daly2k  United States
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Do I need to remove the meter from the chassis to clear any rubbing of the wand? I don't see how I can get at the meter to adjust it any other way but maybe I am missing something? Thanks to all for the help. Again these amps sound terrific. By the way Kent told me to check the meter terminal connections to make sure they were ok. I did this but I didn't measure the across the meter. The connections were tight and I didn't see any corrosion.
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Old 15th December 2013, 10:22 AM   #8
Zen Mod is online now Zen Mod  Serbia
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at least try to measure voltage at meter terminals , for start - then compare with normal value , got from PL boys

you're arriving on point of too much contemplating , zero work

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Old 15th December 2013, 04:03 PM   #9
daly2k is offline daly2k  United States
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Zen Mod--this issue is due to recently retiring. Things that used to take 15 minutes to do now take 4 days. When listening to music with a glass of wine kind of dulls my perfectionist instincts. I depend on NP to be the perfectionist now. Thanks for your help and yes I will absolutely take your advice about the zero work. Now where did I leave my glass of wine? dave
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Old 15th December 2013, 04:13 PM   #10
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Quote:
Originally Posted by CanAm Man View Post
Again, interesting....... would this not indirectly then be a measure of the MOSFET current?
Yep - they are bias meters.
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