I need a copy of the service manual or a set of schematics for a SM8421 SM. The 15Khz display bandwidth is dead, the 5 & 50 Khz bandwidth's have some anomolies in their display. Can anybody help on the oldie but goodie? BTW, it has a center frequency of 2 Mhz and was used with the CEI/WJ 357 lf receiver.. Geoff Greer