Following on from the Mending Stuff thread, is anyone able to take a look at a troublesome circuit and express an opinion on a fix please?
It is the 18Mhz oscillator, feeding the PLL circuit in a rather fancy general coverage radio system. This is the service manual and circuit diagram -
http://www.radiomanual.info/schemi/Y...-8800_serv.pdf
The problem section is the PLL section on page 20, 18Mhz crystal oscillator, which is on the extreme left of the diagram, about halfway down. Q03, Q04, Q05, 18Mhz output of which feeds into Q34 which divides 18Mhz into 4.5Mhz
R18's value seems hypercritical, far more critical than it ought to be, such that the 18Mhz output fails to Q34 a 74LS107. Likewise C20 the decoupling between Q03 and Q04 has several suggestions for its value. No working PLL just causes the display to flash, no reception.
The flashing is an issue reported by many owners and there are as many fixes as there are people with the issue. All of which I have tried unsuccessfully. I have been doing battle with it myself, for several years.