Now that we have a diagram of the circuit we wish to assemble, we need to design a circuit board and contact a company that will produce these boards.
Lumpert contacted the Thuring company twice. Here are the invoices for the two series of boards.
And this is how the board looks like.
The first boards were ordered on 13 August 1985. Twenty boards were ordered and 24 were delivered on 3 September 1985.
On 9 October 1985, Lumpert ordered 35 more boards. These are almost identical to the first ones but not exactly.
The first ones were lacquered with a “solder resist mask” on one side only. [Lötstopp eins.(eitig)] while the second ones were lacquered on both sides [Lötstopp doppelseitig]. Why?
When Lumpert ordered the first series of boards, he anticipated that he would have to correct some mistakes. The presence of the mask would have made it difficult for him to make some corrections. Thus the first boards were lacquered only on one side and for purely cosmetic reasons. (Only the side on which MST-13 is written is lacquered on the first series.)
Lumpert requested that three windows had to be cut from the second boards. (3x Fenster fräsen). He did not ask for this when he ordered the first boards. When the investigators attempted to figure out how many timers had been built, Lumpert stated that he had broken a large number of the first boards. I suspect that he broke these boards while cutting out the windows with a machine that he operated in his own house. And of course he did not ask Thuring to do it because he was hoping to get the boards a bit faster. he clearly wanted them ASAP!
Notice that the circuit tracks had to be covered with TIN (ZINN) on both series of boards. And this is why we know that PT/35(b) is a forgery. While PT/35(b) is covered with pure TIN, the Thuring boards are not! In the Electronics Industry, “Zinn” in German, as well as TIN in English, do not refer to a material but to a process. In this case, the Thuring company has always used a mix of Lead/Tin to cover the circuit tracks. Whoever forged PT/35(b) was obviously not aware of this crucial fact. Lost in translation?