Category Archives: Repair Tips

Some of the repairs I’ve done on electronic equipment

Repair Tip: Viewsonic VX922

*Device:* Viewsonic VX922 TFT monitor

*Fault:* Power light blinks green “long on, short off”. Some signs of backlight activity, but display otherwise black.

*Cause:* Defective “Capxon” electrolytic capacitors on AC power board. Possible issues with defective “Teapo” electrolytic capacitors on the controller board.

*Solution:* Replace all electrolytic capacitors on the power supply board with suitable replacements — e.g. Panasonic FC or FM series. Be aware that space is tight, and as such replacements will need to be the same size as or (vertically) shorter than the existing parts. Vertical height available is ca. 18mm (0.75in).

Replacement of capacitors on the controller board may also be necessary, but be advised that due to a lack of thermal relief on the capacitor pads, desoldering (and soldering of replacement parts) will be difficult using any less than a 100W *temperature-controlled* soldering iron. Try replacing just the PSU capacitors first; do not replace the Teapo capacitors on the controller board unless a PSU component swap fails to repair the monitor.

FIX: Wavy screen on Viewsonic G73fm

PROBLEM: Wavy screen – each line seems to be moved L/R by varying amounts, plus lots of audible noise (whining)

CAUSE: Main filter capacitor has failed

SOLUTION: Replace main SMPS filter capacitor (220uF 450V 85’C). Ideally this should be replaced with a good-quality (read: Matsushita-Panasonic or similar name brand) 105’C capacitor to ensure reliability. SMPS cap is largest capacitor on main PCB and stands around 1.5″ above PCB level. Part designation is C807. Located near D830 diode, L880 transformer. Note that ferrite core on D830 may need to be moved to allow new part to fit – suggested method is a C-bend in D830’s cathode lead to accommodate the ferrite.

NOTES: The SMPS filter capacitor may have expanded, with a bulge in the plastic top seal and potentially enlarged casing and torn/split plastic label. This makes the failure of this part VERY easy to detect visually, without the use of any test gear!

HOWTO: Fix the USB VID/PID on a Freecom DVB stick

A power cut scrambled the USB IDs on my Freecom DVB-T stick this morning… Freecom didn’t want to reply, the supplier just didn’t want to know (“your warranty is with Freecom, not us” – so much for the Sale of Goods Act). Anyway, here’s what I did to fix the VID/PID block on my DVB stick:

Note: this applies to the Freecom 25345-rev.3 DVB stick and may or may not work on others (e.g. the other Wideview WT220U clones with Cypress USB chipsets). Feel free to try this out, but if you bugger up your DVB stick beyond repair, you agree not to hold me liable for your cock-up. But of course, if your DVB stick is fried, you don’t exactly have anything to lose, do you? 🙂

OK, first you need the USB vendor and product ID your USB stick has adopted. Boot off a Linux LiveCD with the DVB stick plugged in by itself – that means NO OTHER USB DEVICES. Then as root run the command:
cat /proc/bus/usb/devices
Ignore all the crap about USB host adapters – what you’re looking for is a line like this:
P: Vendor=1402 ProdID=0255 Rev= 0.00
So we know the DVB stick has adopted the Vendor ID (VID) 0x1402, and the Product ID (PID) 0x0255. Shut down and reboot into Windows.

Rebooted yet? Good. Grab yourself a copy of the Cypress “CY4604 – USB Developer’s uStudio” and install it.

Now we need to do something a little fiddly. Go into C:\Program Files\Cypress\USB DevStudio\Driver, and open CyUSB.inf in Notepad. Search for this:

Note that the USB VID/PID spec line is commented out with a leading semicolon. Remove that semicolon, then do a search-and-replace over the entire file – replace VVVV with the USB vendor ID (without the 0x radix specifier) and PPPP with the Product ID you found earlier (again without the radix specifier). Save the file and close Notepad.

Now plug the DVB stick in. When windows asks for drivers, point it to C:\Program Files\Cypress\USB DevStudio\Driver – the Cypress driver will install.

Run Cypress CyConsole (Start, Programs, Cypress, USB, CyConsole). You should see the DVB stick in the device list. Select the device from the list, then go to Options -> EZ-USB Interface.

Click the “Select Mon” button, then select C:\Program Files\Cypress\USB DevStudio\CyConsole\FW\Vend_Ax.hex (this is the Cypress EEPROM Bootloader).
Click the “Load Mon” button to load the bootloader, and wait for the text to stop scrolling.

In the “Vendor Request” panel (with the “Vend Req” button on the left of it), enter the following values, in this order:
Req: 0xA2
Value: 0x0000
Index: 0x0000
Dir: 1 IN
Hexbytes: (empty)
Length: 256

Press the Clear button, then the Vend Req button. Copy and paste the contents of the log display into a text file.

Now look at the first line of the data that was returned, in my case this was:
0000 C0 02 14 25 02 00 00 08 FF FF FF FF FF FF FF FF

The first byte (C0) is the Boot Specifier – this tells the EZ-USB chip that the data in the EEPROM is a vendor/product ID pair.

The two bytes after that are the Vendor ID in low-byte/high-byte (little endian) order. The two bytes after those are the Product ID, again in little endian byte order. We need to fix these. I want my stick’s VID to be 0x14AA, and its PID to be 0x0225. That means I need to write the following data to the EEPROM:
C0 AA 14 25 02

Hit the Clear button again, and focus your attention on the Vendor Request panel once more. This time set these values:
Req: 0xA2
Value: 0x0000
Index: 0x0000
Dir: 0 OUT
Hexbytes: The data you want to write – in my case, C0 AA 14 25 02
Length: Should be 5, otherwise you’ve done something wrong.

Hit Vend Req again. Another line of text will appear at the end of the log – that’s the data that was sent to the bootloader.

Now set Dir to “1 IN” and clear the Hexbytes field. Set Length to 16 and hit the Vend Req button again. Another line will appear under the ‘data written’ line – it should look a bit like this now:
0000 C0 02 14 25 02
0000 C0 02 14 25 02 00 00 08 FF FF FF FF FF FF FF FF

As long as the first five bytes of the data are correct, you’re done. Unplug the USB stick, wait a few seconds for it to reset, then plug it back in again. Your USB DVB-T stick should now know what it is, and more importantly the drivers will recognise it again.

*ANOTHER* SatPro 4600 problem

Yep, my Satellite Pro 4600 is acting up again. This time the LCD inverter (the second one I fitted) has gone intermittent. I’ve resoldered the two step-up transformers and the piezo transformer, so hopefully I’ve got the problem sorted this time. Of course, if the screen cuts out on me again, I reserve the right to scream and hurl the blasted thing out of a window.
Shopping list item #1: New laptop. Just as soon as I find one that’s Linux-compatible (read as “everything works on Linux without config file hacking or kernel patches”) and has a nice keyboard. Oh, and I like the Toshiba Accupoint ‘joystick’ mouse controller. Trackpads are awful. Of course, now I’ve said that, someone’s going to email me to tell me that I’m wrong, and proceed to insult me in the way only an obsessed Trackpad fanboy can 😀

Toshiba Satellite Pro 4600: Operating with covers removed

Device: Toshiba Satellite Pro 4600 laptop/notebook computer, all configurations.
Repair Tip Title: Operating machine with covers removed for testing

It is possible to operate the Toshiba Satellite Pro 4600 with covers removed. This allows testing and signal probing to be performed easily.
This is done by removing the top casing as per the FRU manual. Connect only the keyboard (it may be possible to use an external keyboard with PC PS/2 mini-DIN connector instead of the internal keyboard) to the motherboard headers. Connect an external monitor and USB mouse, and install the hard disk pack. Power up.
The system will operate correctly in this state, but be careful with screws, etc. while the machine is open on the bench.

Also, a screen cable, inverter and TFT can be converted into a useful ‘remote’ TFT to allow a known-good TFT to be used for testing. The screen cable, TFT and inverter can be purchased new or salvaged from a failed machine. Simply connect the screen cable to the TFT and inverter, then connect the TFT to the inverter. Install in a case if desired, but this is optional. Connect data cable to motherboard, leave TFT positioned in a convenient location.

Toshiba Satellite Pro 4600: No or intermittent audio

Device: Toshiba Satellite Pro 4600 laptop/notebook computer, 14.1″ TFT, 700MHz Celeron, 256MB RAM, Intel 2200BG wireless, 40GB Seagate hard disk.

Fault symptoms: Audio from speakers intermittent, one channel only or not present. Headphone output fully functional L&R channels. Pushing on right-hand side of casing around audio controls may alter fault symptoms.

Fault cause: Poor-quality soldering on motherboard.

Resolution: Dismantle machine, resolder all capacitors near the audio amplifier IC (IC701, Mitsumi MM1517X) and audio riser card, including 2x black electrolytics, with special consideration to larger electrolytics and ceramics. Also resolder filters FL701 and unmarked filter to right of it. Check continuity between FL701 and R speaker connector (PJ703), FL701 and amplifier IC, unmarked and L speaker terminals (PJ702, near keyboard FPC connector PJ64), unmarked and amplifier IC. Also check continuity through both filters.

Also check for bad joints on speaker connectors, audio riser card connector (motherboard and riser-card side) and audio amplifier IC (IC701, Mitsumi MM1517X).

Note: In many cases, resoldering of the filters (FL701+FL???) is all that is necessary. Always resolder filters, but check before resoldering capacitors as capacitor resoldering may not be necessary.

Filters are of an unknown type. May be possible to replace with wire links, but this has NOT been tested.

Use temperature controlled soldering iron (Antex 660TC, or equivalent PACE, Weller or Metcal suggested) set to 350 Celsius and thin 60/40 tin/lead solder for all repairs. Check for shorts with bright light and magnifying glass, remove carefully with desolder wick if present. Follow precautions when handling bare motherboard, as most components on it are sensitive to ESD discharge.