On Thu, Mar 3, 2022 at 06:40 PM, H Kapa wrote:
Hi Jim Adney,
I have a 200CD Ser.605- working on my bench and a few days ago in the middle of another repair my 200CD signal failed,?
In time there I decided to check carefully, the DC voltages were present, but fluctuating in relation to the earth, result R40 of 15K / 10W open, I replaced it with an equivalent but with must the improvised fixing and nothing like the original.
?
So, I ask if you don't have an R40 to supply?
I pulled out my 200CD-605 manual and my box of salvaged parts. In the schematic I find R40 to be 10 kOhm, 10 watt, wirewound, by Lectrohm. I sincerely doubt if there's anything special about this one; anything you can come up with should work as well, but note that it should be TEN kOhm, not 15. I have one which you would be welcome to for the shipping, but I don't think you need it.
The Manual Change pages in the back of my manual say that R40 was changed in 605-65305 and above. It gives a different HP part number, but doesn't say if the resistance value changed, but some of the other changes specify a value change, so this looks like it might be just a supplier change. If your R40 looks original and your serial number is 65305 or above, you should probably stick with 15 kOhm.
BUT, I sincerely doubt if R40 is the source of your problems. I don't think there should normally be any significant current thru it. It sets the DC ground for the power supply, but I can't find any other DC ground connection anywhere else in the schematic. It looks like its only function might be to limit the inrush charging current into C14. Once C14 is charged, the only current thru R40 would be the 120 Hz ripple current thru C40, and perhaps this applies a bit of AC to the grid circuits of V2 & V4, as negative feedback to null out any 120 Hz component in the output.
Do you have a correct 200CD-605 manual and schematic? I think the first thing you should do would be to check all the voltages called out on the schematic. I also recommend that you check continuity thru the two incandescent bulbs. I recommend removing the bulbs and soldering the press fit connections on the sockets. I've had those go resistive. I have a box of NOS bulbs if you need them, but you probably don't. I've never needed to replace one.
One thing that would burn out R40 would be a shorted C14. If that happened, CR1 & CR2 may also have burned out. Those are listed as 1N2359s, but could probably be replaced by 1N4007s. If CR1 & CR2 are dead, that would certainly explain your totally dead 200CD.
