Mending stuff - anyone into radio / electronics

HarryM1BYT · 15th January 2019, 15:32

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.

15th January 2019, 15:32	#1
HarryM1BYT This is my second home 75 Contemporary SE Mk II 2004 Man. Sal. CDTi 135ps, FBH on red diesel, WinCE6 DD Join Date: May 2010 Location: Leeds Posts: 17,273 Thanks: 2,160 Thanked 2,061 Times in 1,586 Posts	Mending stuff - anyone into radio / electronics 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. __________________ Harry How To's and items I offer for free, or just to cover the cost of my expenses... http://www.the75andztclub.co.uk/foru...40#post1764540 Fix a poor handbrake; DIY ABS diagnostic unit; Loan of the spanner needed to change the CDT belts; free OBD diagnostics +MAF; Correct Bosch MAF cheap; DVB-T install in an ex-hi-line system; DD install with a HK amp; FBH servicing. I've taken a vow of poverty. To annoy me, send money.