[Premium-Rx] Premium-Rx Digest, Vol 45, Issue 17

[John Nelson]

>I have changed elec caps out of good practice, never because one has failed
- same comment for the mixer semis.<

I've come across several cases of low capacitance in the 470uF 25V
electrolytics on the 177x IF board and the two chassis-mounted items used
for local rail decoupling in the 1778.  I've also encountered a number of
instances of very low capacitance in the Sprague ValueLytics usually used
for the main reservoir capacitors, including one or two where they have been
visibly leaky. 

>Generally the 177x series are very reliable and straightforward to fix. I
can't say the same for the 1792 which is a pile of ????<

A little unfair in my view. Many 1792s saw 24/7 service in professional and
military applications and to my knowledge they were generally very reliable.
The reported problems with the A6A2 board were often due to neglect of the
backup battery; the damage caused by a leaky NiCd has to be seen to be
believed. On the other hand, BBC Monitoring at Caversham was a large-scale
user of the 1772 and had several persistent problems with them, notably from
overheated PSU wiring. I've also seen a number of 1778s where the battery
has leaked and played havoc with the surrounding metalwork (and the adjacent
decoder board, if the receiver was stored on its side). 

John
GW4FRX