Fluke 2625A, 2635A service manual Introduction, Servicing Surface-Mount Assemblies

Diagnostic Testing and Troubleshooting (2620A/2625A)	5
Introduction

5-1. Introduction

Hydra provides error code information and semi-modular design to aid in troubleshooting. This section explains the error codes and describes procedures needed to isolate a problem to a specific functional area. Finally, troubleshooting hints for each functional area are presented.

But first, if the instrument fails, check the line voltage fuse and replace as needed. If the problem persists, verify that you are operating the instrument correctly by reviewing the operating instructions found in the Hydra Users Manual.

Warning

Opening the case may expose hazardous voltages.Always disconnect the power cord and measuringinputs before opening the case. And remember thatrepairs or servicing should be performed only byqualified personnel.

Required equipment is listed in Section 4 of this manual.

Signal names followed by a ’*’ are active (asserted) low. Signal names not so marked are active high.

5-2. Servicing Surface-Mount Assemblies

Hydra incorporates Surface-Mount Technology (SMT) for printed circuit assemblies (pca’s). Surface-mount components are much smaller than their predecessors, with leads soldered directly to the surface of a circuit board; no plated through-holes are used. Unique servicing, troubleshooting, and repair techniques are required to support this technology. The information offered in the following paragraphs serves only as an introduction to SMT. It is not recommended that repair be attempted based only on the information presented here. Refer to the Fluke "Surface Mount Device Soldering Kit" for

acomplete demonstration and discussion of these techniques. (In the USA, call 1-800- 526-4731 to order.)

Since sockets are seldom used with SMT, "shotgun" troubleshooting cannot be used; a fault should be isolated to the component level before a part is replaced. Surface-mount assemblies are probed from the component side. The probes should make contact only with the pads in front of the component leads. With the close spacing involved, ordinary test probes can easily short two adjacent pins on an SMT IC.

This Service Manual is a vital source for component locations and values. With limited space on the circuit board, chip component locations are seldom labeled. Figures provided in Section 6 of this manual provide this information. Also, remember that chip components are not individually labeled; keep any new or removed component in a labeled package.

Surface-mount components are removed and replaced by reflowing all the solder connections at the same time. Special considerations are required.

∙The solder tool uses regulated hot air to melt the solder; there isno direct contact between the tool and the component.

∙Surface-mount assemblies require rework with wire solder rather thanwith solder paste. A 0.025-inch diameter wire solder composed of 63%tin and 37% lead is recommended. A 60/40 solder is also acceptable.

5-3