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Old 25th Apr 2019, 2:21 pm   #1
Pamphonica
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Default Avo 8 Mk5 flex cables and rivets

I have been fault-finding an Avo 8 Mk5. I have always hated this version as either the flex cables fracture or the soldered interconnect "rivets" through the fixed pcbs fail to make contact.

My fault was no ac volts readings at all and a meter that swung widely, indicating no shunting across it. All other ranges are working, following a little careful switch contact cleaning.

I flipped up the main ac pcb from behind the display and inspected the rivets. As you can see from the photo, many are just pressed in, with no solder at all, although some are soldered. They are soldered on the other side of course, to the flexi-cable.

I re-worked the unsoldered ones nearest the transformer (right hand side under the black wire), using the absolute minimum of heat and extra liquid flux from a pen, but making sure that a small solder fillet now bridged between the rivet and the pcb trace. AC volts now work fine. Excess heat will quickly destroy the flexy pcb so take heed!

My question is whether these un-soldered rivets are an original feature, or a manufacturing flaw.

Whatever, they are a menace!

- Jeremy
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Old 26th Apr 2019, 12:43 am   #2
Skywave
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Arrow Re: Avo 8 Mk5 flex cables and rivets

Quote:
Originally Posted by Pamphonica View Post
I have been fault-finding an AVO 8 Mk5. I have always hated this version as either the flex cables fracture or the soldered interconnect "rivets" through the fixed pcbs fail to make contact.
Excess heat will quickly destroy the flexy pcb - so take heed!
I am in total agreement with your sentiments here. Twice I have been tempted to replace the entire flexy with wires, but have never felt sufficiently confident to do the necessary internal dismantling for that without incurring problems. Why AVO switched from hard wire to a flexy has always been a mystery to me. The AVO 8 is not the easiest multimeter to do maintenance on, so why make that task more difficult?
Right now I have an AVO 8 Mk. 5 which reads low on d.c. volts: this is currently under discussion in another thread, q.v.

Al.
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Old 28th Apr 2019, 4:05 pm   #3
Pamphonica
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Default Re: Avo 8 Mk5 flex cables and rivets

I have now carefully reworked ALL the rivets on both sides, using quick applications of heat from a good, controlled soldering iron, extra flux from a pen and good solder (leaded of course!). I chased the ac volts and amps fault round and round for ages this morning, convincing myself that the transformer was faulty. But finally I reworked more of the flexy-cable solder points on the switch board and the fault has at last
disappeared.
I now have an Avo that passes my calibration checks, at <1% on DC and <2% on AC. Ohms are fine.
Now back in its case and on to the next item on the heap!
-Jeremy
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Old 28th Apr 2019, 4:15 pm   #4
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Default Re: Avo 8 Mk5 flex cables and rivets

Good work Jeremy.

I've just started on an 8 Mk 5 which isn't working on any AC range at all.
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Old 28th Apr 2019, 4:28 pm   #5
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Default Re: Avo 8 Mk5 flex cables and rivets

Well that didn't take me long. Cleaned up the soldering for the flexi cable from those rivet pins from the AC range switch and all working!
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Old 29th Apr 2019, 12:47 pm   #6
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Arrow Re: Avo 8 Mk5 flex cables and rivets

I am investigating a similar fault here on an AVO 8 Mk. 5. In order to make my investigations a lot easier, I replaced all three 'flexy' inter-connectors (one was looking decidedly 'iffy') with multi-strand, insulated wiring. To do that, (and for future reference), I have produced a drawing, showing what connects to where. If anyone would like a copy of said drawing, simply send me a P.M. or e-mail.

Al.
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Old 30th Apr 2019, 10:57 pm   #7
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Arrow Re: Avo 8 Mk5 flex cables and rivets

The AVO 8 Mk5 referred to in my previous thread has now been repaired and the correct calibration restored. All of that is covered in another thread, q.v.

Al.
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