10. Power Supply Repairs, modifications and Teardowns
INSTRUMENT REPAIRS & MODIFICATIONS (IN ALPHANUMERIC ORDER)
# Action Status Problem Manufacturer Model Type Outputs
1. Improve Ongoing Noisy fan Bio-Rad 200/2.0 Electrophoresis 200W 200V 2A
2. Repair TBD Blew fuse Bio-Rad 1000/500 Electrophoresis 250W 1kV 500mA
3. Mod Ongoing 115V/Disable Life Technologies 4001 Electrophoresis 200W 4kV 300mA
4. Mod Ongoing Disable EC Apparatus EC-650 Electrophoresis 200W 6kV 100mA/2kV 350mA
5. Repair Ongoing Ch2 stuck in CC American Reliance PPS-1202 Programmable 240W 18V 4A x2
ELECTROPHORESIS POWER SUPPLIES
I have several electrophoresis power supplies as they were quite cheap.
Unfortunately they often have µC controlled membrane keys to set voltage, current and power that is forgotten as soon as the supply is turned off.
Another annoying safety is a cut-off mechanism that disables the output unless a load is present.
This is perfectly understandable for the intended use working with wet DNA gels that could easily electrocute you, but very inconvenient when used as a general purpose bench supply,
1. BIO-RAD 200/0.2
200W / 200V / 2000mA
text
2. BIO-RAD 1000/500
250W / 1000V / 500mA
text
3. Life Technologies Gibco BRL 4001
200W / 4000V / 300mA
I have a BRL 4001 that looks very similar to the EC600-90.
This website describes overriding the LM3900 comparator circuit that controls this feature on the EC Apparatus EC600-90, a 4000V/300mA/300W:
http://www.kerrywong.com/2019/08/17/teardown-of-an-electrophoresis-power-supply/
Below, Kerry Wong's photos of the EC600-90 mainboard, HV and his No Load detection mod.
Below, my photos of the BRL 4001 mainboard, HV and No Load circuitry section.
It looks like I can copy his mod onto the BRL 4001 to disable the No Load detection feature.
4. EC Apparatus EC-650
200W / 6000V / 100mA or 2000V / 350mA
I bought my EC Apparatus EC-650 before discovering it had the no load safety feature.
Unfortunately the EC-650 does not share the same electronics as the EC-600 and I have not yet been able to identify the section of circuitry that does, let alone obtain a schematic.
OTHER ELECTROPHORESIS PSUs WITHOUT SAFETY CUTOUTS
This link starts with two 500V / 400mA / 200W electrophoresis supplies without this feature:
Pharmacia LKB EPS 500/400; Hoefer PS500XT, and further thread discussions reveal more models.
PROGRAMMABLE PSUs
Text
5. Amrel PPS-1202 dual channel 0-18V 4A Programmable PSU, 3.5 digits, resolution 0.05% 5mV / 0.15% 1.5mA (Amrel is aka American Reliance, bought by Motech)
Problem: Ch2 stuck in CC mode / Noisy fan
This is a nice dual channel 0-18V 4A programmable PSU that I bought without realising one channel was faulty. The seller gave me a 75% refund and allowed me to keep it.
Overview of series here:
a) Ch2 Stuck in CC mode
When the PSU boots it first identifies itself on the LCD and momentarily displays firmware build V8.02A.
Channel 1 works fine but according to the LCD (the little dot to the right of 'CC2') channel 2 is stuck in Constant Current (CC) mode and its output is 29 Volts, way beyond its supposed maximum of 18V:
My first thought was a fault with Ch2's output driver. I looked on the web for a service manual and schematics, and found a post on EEVblog about the 1-ch 18V 4A PPS-1002 that led into a discussion comparing it with a 2-ch 0-30V 3A PPS-1204, which is very similar to my 2-ch 0-18V 4A PPS-1202:
https://www.eevblog.com/forum/testgear/motech-amrel-pps-1002-diagramschematic/
Links are provided for manuals, added below, but full schematics appear unavailable; there is a block diagram in the Service manual, but little else. However the discussion describes an amazing reverse engineering of the address decode logic held in a GAL16V8D PAL on the 1002 which is probably the same in my 1202, and there is a technical description of the 1204 circuitry with a partial schematic.
Popping the lid off my 1202 unsurprisingly reveals a similar design to the 1204: a large mains toroid is mounted behind the front panel and two driver pcbs sit on heatsinks at the rear. The IEC mains inlet feeds into a pcb with rectifiers and large smoothing electrolytics. In the middle two analogue pcbs plug into a small digital motherboard mounted on the base containing a Temic TSC80C31-16CA µC, a TI TMS27C512-10 Eprom, an Atmel 93C46 EEP and a Lattice GAL16V8D-25LP PAL. Chip manf dates are circa 1999.
As with the author, I too removed my Eprom and EEP and saved the contents. Wix won't upload BIN or HEX files, so I uploaded both BIN files below as .TXT files. If you D/L them you need to rename them .BIN.
The analogue boards are identical, and each has an identical connector that leads to one of the output driver blocks. The analogue pcb nearest to the mains toroid at the front is Ch1.
Swapping their positions in the mobo revealed the fault appears to lie with analogue board 2, as the LCD CC indicator swapped from CC2 to CC1, and I was able to correctly program Ch2 and get a valid voltage out but no longer on Ch1 which is now stuck at 21V. This suggests the output driver stages are ok.
However there appear to be a couple more issues as Ch2 LCD voltage is incorrectly shown as fixed at 13.868V with over-voltage protection set, and Ch1 is shown as 'OFF' despite the presence of 21V.
The next move is to try to debug analogue pcb #2. I'll first see if it's possible to build an extender to raise analogue pcb #1 above pcb #2 to facilitate easy comparison in-situ.
b) Noisy fan
The fan is very loud and is on all the time regardless of load. Maybe fit a quieter pwm fan? Noctua?
It's 80mm square x 23mm thick and has only 2 leads. The fan label says: AVE AV825H12B ZP 12V 180mA.
I assume the H means high speed/power as on the net I found a 120mA M model and 90mA L model.
I assume B means it has better Ball bearings than the more common S model which I'm guessing means it has cheaper/noisier/shorter life Sleeve bearings. I can find nothing more about it or the manufacturer. Noctua explains fan bearing differences here: https://noctua.at/en/sso-bearing
This video shows a simple mod to an Amrel PPS-2322 that only turns the fan on when a heatsink is hot:
https://www.youtube.com/watch?v=XUs7ZQLJke0
I'd rather have one that runs it slowly instead of flat out.
The same guy above also has a teardown of an Amrel PPS-2322:
http://www.kerrywong.com/2015/05/06/amrel-pps-2322-programmable-power-supply-teardown/
text
text
µ Ω ± ° ⌠ ⌡ ∫ │ ─ √ φ θ Θ ∂ δ ζ ξ ς λ ψ ω τ µ Ω ∆ Δ ∑ ∏ π Ξ ○ ≠ ³ ² ±