How to Fix and Upgrade Your Unit
The whole range of Chandler Limited products relies on the same robust power supply design, which delivers ±28VDC along with 48V phantom power for condenser microphones. For anyone servicing a Chandler Limited power supply, it’s useful to understand how it’s built: Chandler engineered it around a dual primary mains transformer, followed by a bridge rectifier, an LM317 for the positive rail, and an LM337 for the negative rail. Additionally, the raw DC generates the phantom power, regulated through an LM317HVT — essentially a high-voltage version of the LM317.
The circuit isn’t available, but the PCB shows a standard design with 4700uf capacitors in parallel before the regulator, a 100uf capacitor at the output, and 5k trimmers on positive and negative supplies to adjust voltage. LED indicators show voltage presence in each supply.
Main Causes of Failure of the Chandler limited Power Supply
Most of the Chandler Limited power supply units stop working when the electrolytic capacitors inside dry out and when the regulators fail. Three factors cause this phenomenon:
1- The bridge rectifier outputs high raw DC voltage to the capacitors, higher than the rated caps can sustain.
2- High temperatures inside the power supply occur because the regulators and LED resistors get hot and are located close to the capacitors.
3- Age, or better years in service.
These three factors cause these power supplies to fail. Moreover, the limited height clearance inside prevents voltage upgrades for the capacitors. However, here is my solution
How to Fix and Upgrade Your Chandler power supply:
STEP 1:
Remove the top cover of your Chandler Limiter power supply. Remove the old capacitors and regulators. Without a silkscreen on the PCB, remember the orientation of each component for a confident and correct repopulation.
STEP 2:
Drill 2 holes on the chassis where you will bolt the positive 317 and negative 337. Use an insulating kit for each TO-220 regulator to prevent continuity between the pins and power supply chassis. If you fail to do this, the regulators will short and go up in smoke! Use flying wires to connect the regulators back to the PCB. Their orientation is now reversed, so make sure you reverse the wires as well, I used heat shrink to insulate the pins of the regulators.
STEP 3:
Repopulate your Chandler Limited power supply PCB with 105°C, 50V capacitors sized under 30mm tall and 18mm wide. Since I recapped this power supply, I found a document where Chandler suggests using 2x3300uF @ 50VDC instead of 3. Here is the document from Chandler
STEP 4:
Cut the LED resistors off to minimise the heat generation inside the power supply. The LEDs light up independently of the power supply output, so their illumination doesn’t show if the power supply is working correctly or not. A 2W resistor supplies these LEDs, and since it is placed in close proximity to the capacitors, it increases their heat and therefore shortens their lifespan.You can disconnect these LEDs, as they are not essential for the power supply functionality. The resistors are shown in the picture below.
Simply cut them off using a pair of snips and you should get the result below:
STEP 5:
This is the final step, it’s now time to line up the power supply. Using a Digital Multi Meter ensure that the voltages at the output are as follows:
Test between Pin 1 & Pin 2 = +48VDC
Between Pin 1 & Pin 3 = +28VDC
Test between Pin 1 & Pin 4 = -28VDC
You can’t adjust the phantom power supply, so in the UK, where the mains voltage is 240V, I measure roughly 49VDC, which works perfectly fine. If you have followed the steps correctly you now have a brand new power supply.
List of Components For The Chandler Power Supply Repair Process
Whether you use the Chandler updated capacitor layout or the one I used you will pretty much get a new power supply for just under $150 in parts. You can purchase most components for your Chandler Limited power supply repair from trusted electronic resellers such as Mouser, Rapid, RS, and Farnell. If you want to proceed and complete the repair yourself, use the list of components here, which follows Chandler’s updated document. I have not tested all of these components myself but they look correct on paper.
Check out the Telefunken V676a repair article — you can find the link here.