Can a conviction without a lawyer be used to revoke probation because the conviction was unconstitutional?

But more basically, respondent argues regardless of the fact that appellant was convicted without the assistance of counsel or waiver of that right, the conviction can be used to revoke probation because he was guilty of the [226 Cal.App.3d 497] offense charged. Whether appellant was or was not guilty of the underlying offense is irrelevant in determining whether the unconstitutional conviction can be the basis from which additional penal sanctions flow. (People v. Coffey, supra, 67 Cal.2d at pp. 214-215, 60 Cal.Rptr. 457, 430 P.2d 15.)