Next Patient: MEP 805B / 806B AVR100

[peapvp]

Folks,
On our next Endeavour we will have a look at a AVR100 made in 2005

Fault:
Output voltage drops consistently after it has been adjusted to 208VAC after startup

First Step:
Dissolving Silicone based Conformal Coating

 

[peapvp]

Update:

Status after 24 hours of stripper bath




The Sticker “Made In China” was applied to the circuit board right below the small transformer and floated to the top since this area cleared already.

George Busch…….,..,

 

[Evvy Fesler]

What chem did you strip it with?

 

[peapvp]

What chem did you strip it with?

Hi Evvy,

sorry, but that’s something I cannot disclose.
This is 17 year old domestic Chinese conformal coating.
Hence the chunks. US made Silicone Conformal Coating dissolves fully in this Stripper.
Any commercial stripper for silicone based conformal coating {edit} will probably desolve this coating. A Chinese Stripper will probably work better {edit}.
The Conformal Coating we use is classified.

Peter

 

[Jetcruzr]

Hello peapvp,

I am working on my MEP 806B today. At initial startup, the voltage was well over 220VAC, but it steadily declines the longer the machine runs. It is now down to around 185VAC. Voltage adjustment switch as well as screw on AVR are unresponsive. Any suggestions? It seems like you are having a similar issue.

Thanks!

 

[peapvp]

Hello peapvp,

I am working on my MEP 806B today. At initial startup, the voltage was well over 220VAC, but it steadily declines the longer the machine runs. It is now down to around 185VAC. Voltage adjustment switch as well as screw on AVR are unresponsive. Any suggestions? It seems like you are having a similar issue.

Thanks!

Hi Jetcruzr,
Same issue.
i will post the troubleshooting and repair info here on this thread as we go along.
Peter

 

[peapvp]

Update:

Stripper Bath Time: 60 Hours

This conformal coating is definitely not MIL-STD
The filler you see here is app 1/3 of what was still floating in the stripper bath.

This should be a warning to anyone wanting to strip these boards in a batch stripper.
This stuff here will clog up your filters, strainers, nozzles and pump(s).
So, a large scale reconditioning of these GAC Boards (100, 102 etc) is out of the question.
Three or four resistors have to be replaced as a result of stripping
Transformer is in the oven for 24 hours to dry @ 125F

Caps have to be checked with the rest of the board





More to follow, stay tuned

Peter

 

[peapvp]

Update:

The two ceramic smd caps are open (infinite ESR and capacitance), normal Value presumable 22nF/100V

The three electrolytic Caps 100uF / 400V show bad ESR and have capacitance range of 260uF to 270uF

The two axial Electrolytic Capacitors 47uF / 100V are good showing 47uF with good ESR (0.2 Ohm)

That's it for the moment, next update either later today or tomorrow

Peter