Solving problems.

This page lists possibly problems with the decoder, and how to solve them.

1 The PLL locks, but the
sync LED doesn't turn on.
The input data
is inverted.
  • Connect pin 9 and 10 of CON2 (forcing pin 30 oc IC1 low.
  • Or add an inverter in the data input.
  • Or remove one of the inverters IC3D or IC3C from the data path.
2 Recording stops unexpectedly. Signal quality is low (sync LED is flashing sometimes) Change the "Record times' parameters in the Preferences (chapter 'Record'). Increase the 'Stop after' number. E.g. a value for (C)HRPT of 60 (=60/6=10 sec) and 570 for HRI (=570/57=10 sec) should bridge a period of 10 secs out-of-sync.
Signal quality is good; sync LED is not flashing.
Probably crosstalk on the par. port cable
Disconnect pin 15 of par. port, connect pin 15 (at PC side) to ground instead. This disables 'automatic recording stop' after out-of-sync. If that solves the problem then there is crosstalk on the par. port cable. Try another cable.
3 Leds of channels selected switch off by itself after recording has started. Connecting pin 20 of left FPGA to ground after channel selection and before start of record solves the problem. Crosstalk on the par. port cable. Increase R14 and/or C11.
4 Pictures are very noisy if more than 1 channel is selected. If 1 channel is selected pictures look fine. Crosstalk on the par. port cable. Try another par. port cable.
5 Distorted line (or line parts), decoder doesn't go out-of-sync Xtal oscillator (second FPGA) doesn't work properly.
  • Make sure XTAL is parallel resonant type.
  • Try R10=0 ohm (now 220 ohm, should be between 0 and 1k).
  • Try C5=40pF (now 10 pF). This will lower voltage swing on osc. input.
  • If nothing helps: replace by external oscillator, connected to pin 53 (remove X1, R9, R10, C4 and C5.) This problem SHOULD, however, be solvable!
  • Par. port cable.