The manufacturer however admitted that that SCPs on Boeing 601 spacecraft launched prior to August 1997 contain tin-plated relay switches that can experience electrical shorts when several factors are concurrently present. If this applied to all 601-model satellites launched until July 1997, at least 30 of HS 601s in orbit would be equipped with the dreaded tin-plated relays.
The SCP is the on-board computer that controls the satellite. There's also at least one backup SCP aboard every satellite.
The relay serves as an on/off switch within the SCP. Under certain conditions, tiny crystalline structures (known as "tin whiskers") can grow and bridge a relay terminal to its case, causing an electrical short which blows fuses.
| Name | Launched | First SCP failure | Second SCP failure |
|---|---|---|---|
| Optus B1 [Optus] | 13 August 1992 | 21 May 2005 | - |
| Galaxy VII [PanAmSat] | 27 October 1992 | 13 June 1998 | 22 November 2000 |
| Galaxy IV [PanAmSat] | 24 June 1993 | (not caused by 'tin whiskers') | 19 May 1998 |
| Solidaridad 1 [SatMex] | 19 November 1993 | 28 April 1999 | 27 August 2000 |
| DBS-1 [DirecTV] | 17 December 1993 | 4 July 1998 | - |
| PAS-4 [PanAmSat] | 3 August 1995 | 3rd quarter 1998 | - |
| Galaxy IIIR [PanAmSat] | 15 December 1995 | 21 April 2001 | 15 January 2006 |
| DirecTV 3 [DirecTV] | 9 June 1995 | 4 May 2002 | - |