Office Depot Ativa Wireless G Router AWGR54 by Belkin

[severach]

FCCID: RAXWG4005G
P75233 AWGR54 WG4005G-LF-AK 141400520017J REV:01
U1: Atheros AR2317-AC1A with stick on or solder on heat sink
U8: IC+ IP175C LF 5 Port 10/100 Ethernet Integrated Switch with integrated linear regulator driver
Q4: UTC 2SB1412 B1412 PNP HIGH VOLTAGE SWITCHING TRANSISTOR C259:3.3v -> EC180:1.88v->L79->EC179 regulated by the IP175C
U10: Anpec APM9435 P-Channel Enhancement Mode MOSFET
U12: Matrix Microtech MT34063M Universal DC to DC Converter C289:12v -> C291,C169:3.3v
D11: SK24 SMD 3.3v freewheel diode
U11: ISSI IS42S16400B-7T 64 MBit SDRAM 1Mb x 16 x 4

iESR=in circuit ESR
ESR=out of circuit ESR
WV=Working voltage of a functional unit

C289: Taicon VT 100uf 25v 6.5x12 iESR=0.75 ESR=0.85 WV=12v transformer voltage
EC179: Elcon 47uf 25v EYA 5x11 iESR=0.03 ESR=0.12 WV=1.88v
EC180: Elcon 47uf 25v EYA 5x11 iESR=0.03 ESR=0.12 WV=1.88v
EC182: Elcon 47uf 25v EYA 5x11 iESR=0.03 ESR=0.12 WV=3.3v
C291: Elcon 470uf 10v 6.5x12 iESR=0.05 ESR=0.55 WV=3.3v parallel with C169
C169: Taicon 100uf 25v 6.5x12 VT iESR=0.05 ESR=0.85 WV=3.3v parallel with C291

6 units, all unreliable. All fail, some run for days, some fail within minutes. The wireless and web configuration may work for a short time after the router dies and cuts off the Internet. A power cycle and they are working again. No obvious bad caps. C169 and C291 are in parallel and are very different. Maybe the circuit was designed for two 470uf 10v caps and the smaller cap got substituted by mistake or to save a penny. The Taicon datasheet does not list ESR for C169. 1 ohm ESR is appropriate for a 100uf low ESR capacitor. The Elcon EYA data sheet shows 0.13 ohms impedance for a 470uf 10v. The series of C291 is not labeled but if it were an EYA, 0.55 ohms would be 5 times the proper value.

With the router becoming unreliable when the Elcon 470uf reaches 0.55 ohms the perfectly good 1 ohm Taicon 100uf is completely useless in position C169. In C169 I put a Panasonic or Rubycon 820uf 6.3v which have an ESR of 0.02. At 1/5th the ESR of the best original, my cap takes the entire load so C291 is no longer important. EC179-182 have way better ESR than anything I can supply. The ESR of C289 does not need to be very low.

One cap done!

It appears that many low cost networking products have the same flaw and the same fix works for most of them. The engineers design a reliable circuit. Bean counters cut costs until the design is marginal but still works for most of the warranty period. Semiconductors aren't easy to cut because they don't substitute well. Capacitors can be cut right to the edge of reliability. The capacitors slowly degrade which stresses the marginal circuitry to the breaking point. Soon the product is unreliable but can be coaxed into functioning. Eventually the product fails completely. The capacitors look and test good so the problem is assumed to be in unfixable circuitry and the product is discarded.

Caps more reliable, larger, and with better ESR than the originals in the right places makes the circuit no longer marginal allowing the product to be as reliable and long lasting as the engineers originally intended.

So far all indications are that this fix is perfect. All test runs have passed and the deployments I've done are working flawlessly. Fortunately I ran across another unmodified unit so I can provide scope pics.

3191-Top: 12v at C289
3191-Bottom: 3.3v at C291

Cap testing at C289 shows that the 12v waveform can be smoothed out but it does not improve the 3.3v waveform. Cap testing at C291 shows the wave can be smoothed out substantially. Unfortunately a 1500uf cap test on C291 surprised the MT34063 and burned it and the IP175C and AR2317 and IS42S16400B out. APM9435 was still good. Fortunately I can get scope pics from another already serviced unit.

C169: Rubycon MBZ 470uf 16v

3192-Top: 12v at C289
3192-Bottom: 3.3v at C169 with Rubycon MBZ
3193-Top: 3.3v at C169 with Rubycon MBZ
3193-Bottom: 1.8v at EC179

Reducing the ripple from 40mv to 10mv on the 3.3v rail would be why this fix works so well. A better cap could reduce it even more.

[Brian10962001]

Re: Office Depot Ativa Wireless G Router AWGR54 by Belkin

Very well done!

[jakdedert]

Re: Office Depot Ativa Wireless G Router AWGR54 by Belkin

Kudos! I have one of these disasters which failed to work right out of the box. In fact, I'm going to open a thread about failed wireless routers in general. The failure mode I experience most often is when the wired ports continue to work, but the wifi does not. Remote machines can 'see' the router, but cannot connect. This is common (for me) across many different models of many different brands. I almost always open them up, but not seeing anything obviously amiss, just set them aside. Your post gives me some hope that something 'could' be done with them.

[grgz]

Re: Office Depot Ativa Wireless G Router AWGR54 by Belkin

Hello everybody, first post here.

Found this thread from google and i'd like to add that exactly the same hardware is an access point from Airties, the AP-400.

After two years of trouble free operation i'm facing the same problems with you.

When you plug it on power all the leds are lightning but you can't connect on it either from ethernet or wirelessly, although you find it at the available wireless networks.

I'm gonna try the solution mentioned above and i'm gonna give some feedback.

[Lex-]

Re: Office Depot Ativa Wireless G Router AWGR54 by Belkin

Hello severach,

thank you for your interesting work, but please consider the following:

You wrote:
C169 and C291 are in parallel and are very different. Maybe the circuit was designed for two 470uf 10v caps and the smaller cap got substituted by mistake or to save a penny.

Ok, but if you check the typical step-down application circuit on the MT34063M datasheet or even the MC34063A one, you can verify that the capacitor values are exactly the recommended by the manufacturer (Vin 100uf, Vout 470uf, Filter 100uf)...

https://cdn.badcaps-static.com/pdfs/...286d7e48b9.pdf

About the optional filter shown in datasheet, maybe the problem is that isn't really a filter on router circuit due the missing 1 uH inductor...

Then maybe the main functional problem of these routers is related to the following note on datasheet:

Application concerns:
To get the best regulation performance, Low ESR capacitors at Vout are suggested.

Then maybe the problem isn't really related to the capacitor value, probably is more related to use the correct or suggested (ESR) type of capacitor...

Of course an interesting experiment to clarify this issue can be the use of the Rubycon MBZ 470uf 16v in place of C291 (not C169), and check the waveforms with the scope again, let us know what you think.

Thank you.

[severach]

Re: Office Depot Ativa Wireless G Router AWGR54 by Belkin

The sample with the 470uf and 100uf have a coil in between to make up a PI filter. The 1.8v supply has a coil but the 3.3v supply doesn't. The trace runs from C169 to C291 with no filter coil and the two capacitors are almost equidistant from the buck coil so swapping the position won't have any effect.

For some units the upgraded capacitor isn't enough. They last longer than the 5 minutes they used to but eventually lock up in a few days. I've had units where only the radio manager process crashes and other units where the entire processor crashes. All the ones I have back have a small puck for a heat sink and not the finned heat sink as shown. Some still crash with oversize heat sinks.

Turns out there aren't many wireless routers that can be fixed with one cap. This one was because the 1.8v supply was well made. Only the 3.3v supply was a poor design. Most other units more supplies and many supply disasters. Keeping stable power to the processor isn't easy when a transmitter is pounding the supply constantly.