Mark IV voltage regulator

[jawbreaker]

I have a late model mark iv with the large black cinch plugs. Everything works but when I turn it on the transmitter display blinks on ch 1 through ch 5 for a minute till it warms up (vco unlocked??). Also the voltage regulator board runs extremely hot. My question-- Is the regulator supposed to run hot and if not would this cause the blinking? I would like to upgrade the pll board if possible to get more coverage. Thanks!

[mark4]

The -9 volt regulator board does not run all that hot.
But mounted atop that 10watt dropping resistor sure will seem that it is. Slowly cooking it all those years. Never figured out why they decided to put it there. There are better places it could have been mounted. The 5 volt regulators mounted to the PLL Can, do get quite warm. All those old TTL chips draw quite a bit of power. I upgrade that regulator board and the PLL.
Those old electrolytic caps go in the trash along with those 5 Volt voltage regulators. Among other upgrades.
But blinking on 1-5 sounds like the voltage control in the PLL is out of calibration. The correct way to cal it is remove the PLL from it's can and make sure it's grounded to the chassis of the radio.
Make sure not to let anything short out when doing this one wrong move could kill it. Adjust C122 for 1.8V on channel 1 should be below 3.4 Volts on channel 40. (test point is C106 to ground). The 25V 25uf cap in the PLL-could also be a 22uf 25V cap. The PLL should also be checked for the latest factory modification. A string of diodes located at the bases of Q103 & Q104. This mod was Incorporated in later PLL production boards.
Well here's a place to start. Mine has a custom programmed ROM that works out great. But there is allot more to it than just putting in a custom ROM. Also many other things can cause a blinking display. Just a place to start. May very well be another problem. They can be repaired I use mine everyday. Hope this helps.

[jawbreaker]

Thanks for the info. I adjusted c122 so now the blinking stopped. It has the extra diodes on Q103 & Q104. Someone modified this radio to go up to ch 60 on the display but no lowers. I would like to change that to get more coverage. After this radio I have a mark III to expand and a Tram D201 to bring alive. I have always had an interest in these radios but never got into working on them until now. I have all the test equipment and know how to use it. Thanks for the help!!

[mark4]

Good to hear it worked out.
You may run into problems trying to get 60 channels out of that PLL without a modification. It just doesn't have the range stock.
Or maybe yours will behave with 60 instead of 90