GRiDCase 1520 DC-DC Converter Repair

While diagnosing a RAM failure in my more sickly GRiDCase 1520 I noticed an unpleasant odour coming from the rear of the machine. Pretty soon it started behaving erraticly, rebooting at random. It's capacitors again — this time in the DC-DC converter module. Time to break out the soldering iron!

Extracting the DC-DC converter requires opening up the computer. It was immediately obvious that at least one large capacitor had leaked: underneath the DC-DC converter a brownish liquid was pooling. It also coated the lower half of the converter PCB :-(

DC-DC Converter Overview

The DC-DC converter takes the DC input to the system (16.24V from battery/PSU bay or 9-20V from external barrel connector). It converts this to the various voltages required for the rest of the system.

There are multiple models for the GRiDCase 1500-series DC-DC Converter:

LCD-115, GRiD part number 104144-00. Used with the two LCD display options. Provides −15, +5, and +12 DC outputs plus switchable 100VAC.
PLASMA-116, GRiD part number 104145-00. Used with the two plasma display options. Provides −15, +5, +12, and +33V DC outputs.

The machine I'm repairing here had an LCD display.

Top view of DC-DC converter — Top view. Markings read: M/N: DC20W4P-115F, S/N: 16780, LIEN ENGR. S.D. C.A.

Front view of DC-DC converter — Front view.

Bottom view of DC-DC conveter — Bottom view.

Removing the Capacitors

Closeup of burst capacitor — This capacitor has split on it's side.

Cluster of leaking capacitors — Multiple capacitors in this cluster have leaked fluid from their bases.

Removed capacitors and insects — I removed all the large brown and blue capacitors. The small blue capacitors appeared OK so I left them alone. I also removed a couple of insects that had crawled in and gone cripsy next to the power transistors.

PCB after capacitor removal — View of the PCB after removing the capacitors. Note the brownish gunk where the capacitors sat.

The capacitors I removed and their values were:

Designator	Capacitance µF	Voltage V	Max Temp °C	Height mm	Diameter mm	Lead Spacing mm
C1	470	25	105	21	10	5
C19	2200	10	105	25	13	6
C20	220	16	105	12	5	5
C30	47	100	85	17	10	6
C31	47	100	85	17	10	6
C35	47	100	85	17	10	6
C61	1000	25	105	25	13	6
C71	47	50	85	12	6	3
C72	47	50	85	12	6	3
C73	3300	6.3	105	20	10	5
C74	470	6.3	105	12	10	5
C76	10	10	85	11	13	2
C80	1000	25	105	25	13	6
C81	1000	25	105	25	13	6
C82	3300	6.3	105	20	13	5
C83	3300	6.3	105	20	13	5

I managed to source replacements that met the capacitance; met or slightly exceeded the voltage and temperature rating; and were physically the same size or smaller.

DC-DC Converter Overview

Removing the Capacitors

Fitting Replacements