On May 25, 2010, at 10:13 AM, Rodolfo Gil wrote:
I have an experience with bad flyback transformer in Mac Plus. Flyback transformers have different ways to fail. In my case, there wasn’t high voltage on the CRT but I could hear the start up chime and activity in the FDD (loading OS). I took away the fly back transformer from a Mac 512K analog board (same part number). This model of flyback is discontinued.
There are (or were) a great many different models of (horizontal sweep) flyback transformer.
(The PSU also uses a flyback transformer, so there are really two of them on a 120K, ..., Plus analog board).
The early non-bleeder-type sweep flybacks are no longer available. Good thing, too, as these can be dangerous.
Since at least with the Plus, if not earlier with the 512K, all sweep flybacks have been of the bleeder type.
(A bleeder-type means that as soon as the power is removed from the machine, the bleeder resistor which is integral with the sweep flyback acts to bleed-down, and hence remove any remaining high voltage within the CRT. The CRT is actually acting as a filter capacitor, and it is the charge which remains on, and within the CRT which is the source of trouble).
There are so many part numbers which are compatible with the 128K, ..., Plus board that it would be impossible to identify all of them.
Just ask for a bleeder-type Plus horizontal sweep flyback and you will get the right one.
Also, one of the primary reasons for flyback failures is failure of the very special non-polarized, high temperature rating, horizontal coupling capacitor.
This capacitor is almost impossible to find now. -- ----- You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To leave this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/
