Inside the digital cluster, there is a power supply module for all of the blue vacuum fluorescent gauges (fuel, oil pressure, engine temp, voltage, and rpm.) You need an electronics guy to remove the rear circuit board to get to the small power supply circuit board that is attached to it. Replace the 43uF electrolytic capacitor (a 50 cent part) and that may fix the problem. Another possibility is the two 2SC3328 transistors (about $1 ea.) More details here: http://chevroletforum.com/forum/s-10-blazer-20/92s-10-blazer-digital-dash-2034/
The instrument cluster is a bit of a nuisance to remove, but there are instructions elsewhere on the web. The hardest part is removing the climate control cluster on the right hand side so that the instrument cluster escutcheon can be pulled out.
While you have the cluster out, replace the two PC194 lamps that light the PRNOD21 indicator and the tach yellow and redline markers. No need to replace the others.
Dear Sir Thanks Have a 94 S-10 Blazer with a almost dead speedometer. It will not illuminate ,brighten up. When dark you can barely see the first digit working, the second just show - VIN: 1GNDT13Z5R215556 Temp gauge dead but that is the sensor on rear LH side, tomorrow. All warning lights are gone ,but they showed up for a few minutes. Crawl under dash to morrow and find out. Will faulty ign. switch cause any of this faults? Thanks in advance. have a great day in America Any answer to my awkward questions will be greatly appreciated. Regards Hans A.Skontorp Stavanger Norway