Racing fans may not know much about diodes and 50-volt feeds, but they were made aware of their importance yesterday at Laurel Race Course.

An electrical glitch held the track's tote board hostage throughout the 10-race program. The problem was particularly acute during the first seven races, when the odds on the infield board were largely indecipherable and payoffs had to be displayed in the space normally used for messages.

Television monitors at Laurel and Pimlico functioned without difficulty, giving fans the prerace win odds and exacta payoffs normally available.

According to Jack Begor, engineer in charge of the American Totalisator Co. system, the infield board was victimized by a bad electrical feed. The problem did not infiltrate the system's central computer -- known as the Blue Train -- into which wagers from all mutuel machines are fed, and odds and payoffs calculated and displayed. That allowed the in-house monitors to remain unaffected.

By late afternoon -- after the last race -- Begor said he believed the root of the problem had been isolated within the infield board.

"We'll get it tonight for sure," he said. "We've pretty much pinpointed it. We'll stay and get it all cleaned up before we leave here, no matter how long it takes."

Laurel does not race today.

In running standard tests before yesterday's races, workers for AmTote -- an independent company contracted by Laurel, Pimlico and other tracks -- realized the problem. Experts were called in and employees spent the day in search of the glitch with modest results. The odds board was nearly functional for the final three races.

"This was way beyond the normal scope" of day-to-day problems, Begor said.

"Those types of things happen," said Elizabeth Quill, Laurel's parmimutuel director. "Just thank God it was on a day like today and not Preakness Day."

Bettors were inconvenienced by the foul-up, but apparently were not too upset. The day's wagers totaled $1,200,458, about $5,000 below the per race average for last year's card, when $1,381,247 was bet on an 11-race program. Mare Unhurt in Dash

Local Thriller was not injured Sunday when she broke free before the My Juliet Handicap, according to trainer Mert Bailes. The mare ran nearly a mile at full speed on the track, then jumped the outside rail and galloped along the tree-lined backstretch before being collared in the stable area. . . .

Jockey Kelly Castaneda ended a 101-race winless streak yesterday astride Primms Cup ($11.20) in the fourth. His previous winner had come March 27. . . . Ron Franklin is back from Chicago, where he was working for trainer Bud Delp, and may begin riding here this week. . . .

The Maryland Racing Commission granted stays to Mike Luzzi and Greg Hutton after the jockeys were suspended seven days each for causing a two-horse spill Saturday. Each will have a hearing before the nine-member commission.

Edgar Prado did not officially file a request for a stay following an unrelated infraction and has begun a seven-day suspension. . . .

Ten Keys received a race-high 124 pounds for the $100,000 Fort McHenry Handicap July 4, and trainer Mike Pino said he is giving the race strong consideration. Pino won his fifth race from seven starters in this meet as Trae's Prospect beat $12,000 claimers for his fifth straight triumph.