DCC -27 voltage too high

[jim43bob]

Hi, bench testing a DCC4 2 code A. I have recapped 311125-D board. With the totalizer plug jumpered I get the following voltages.

-31v,-13.5v and +25V

According to Rons guide the +25 volts is ok but I have more than a difference of 15.5 v on the negative side. I have not changed the four diodes yet to 1N4004 or better and being somewhat of a novice I'm wondering on what to change or check next to lower the -31v to within range as the -13.5 volts looks acceptable.

Any help appreciated!

[Ron Rich]

31 volts is to high-- check resistors--is the transistor on the board, the correct one-- good ? Ron Rich

[jim43bob]

Hi Ron, I have pulled and checked all resistors and replaced any that were out by more than 5% (changed a  total of 7). Still have same result as far as voltages. I have to admit that I changed all the electrolytic caps but did not change the one .33 uf mylar cap. Will try that next. I have a spare 311125-D board that I put in DCC and voltages are fine with it installed. Only thing left to change after that I can think of is zeners and the transistors!

[Ron Rich]

Jim,
Change the 2N2905 transistor-- see the DCC service notes in your copy of my Seeburg MicroLog Trouble Shooting Guide--
Ron Rich

[jim43bob]

Hi Ron, I changed both Q3100 and Q3120 with the same results.I contacted an old friend who had become quite the electronic guru and he suggested I check the capacitors and diodes for any AC voltage leaking and sure enough zener CR3110 a 13 volt which I did already replace was way out of its range as well as diode CR3112 a 170 PIV which had failed altogether. My voltages are now within tolerance and no longer suffer from the scan twice syndrome.I now have some other problems cropping up and just checking with you mech guide on how to proceed. Will probably be chiming in again for help once I read on how to proceed.
Many thanks once again!
Jim

[Ron Rich]

Hi Jim,
I HATE, installing new,bad parts !! But I do have one question--you claimed the -13 was OK ?? Ron

[jim43bob]

Hi Ron. The -13.5 volts changed to -14 and the -31 volts change to -28.5 volts. I had checked voltages using an analog and a digital meter. They were now within the 15.5 volt differential and mech detented at whatever selection I picked. I did end up with a strange problem though in that the mech would detent and partially load record (sometimes) and there was a thumping sound when scanning from left to right. I had cleaned mech as you describe in your book and oiled. The only thing I could think of was that the clutch was not moving freely enough and under close examination there was still old lubriplate on it. I removed the clutch which I had never done before ( thank god for your instructions on how to do it) cleaned reassembled and oiled and everything works perfectly now! I do have silly question if you or anyone could answer and that's to do with the lower front cover of my Entertainer. There is/was a thin black foam in behind the metal screen that's in front of the subs.Has anyone replaced this with just black speaker material or did they use thin foam and would it really make a difference in what I use?

Jim

[Ron Rich]

Hi Jim,
Glad you got it running ! That "foam", if I recall was a gray colored "weatherstripping" material. I think it was there to prevent rattles-- not 100 % sure on that--but about 89%-- lol-- I think you could use anything (such as self-sticking weatherstripping tape) to keep that metal from resonating--- Glad the Guide helped --thanks for purchasing it ! Ron Rich

[jim43bob]

Hi Ron.The foam I was talking about is the piece about 20 inches x 29 inches that is sandwiched between the front screen of the hinged cover that has the round openings for the subwoofers. It looks like the foam that a lot of residential dehumidifiers use for a filter, but I have not found anyone that carries that large a piece of material but cloth speaker covering is easy for me to find if it's ok to use.

Jim

[Ron Rich]

Hi Jim,
I think it would work as long as it did not muffle the sound-- Ron Rich

[jim43bob]

Thanks Ron!
Will give it a try, it's not expensive and easy enough to remove if it does muffle the subs.

Jim