More resistor replacement.....sigh.....

[andylevine]

So, I may be being picky, but I'm still going through my the electronics of my STD4 Mardi Gras project and I'm shocked at how many of the resistors are not only out of original tolerance (most 10%) but not even CLOSE to being good.  The amp I probably replaced 4-5, but in the DCC I would say easily over 2/3 were WAY out of bounds.  Today I tested the the crossover (SN12) and the lighting 5 bit sequencer (5BS1)... both of the resistors in the SN1 TOTALLY gone (really... like 1 ohm each  All THREE of my meters!) and 10 of the 21 in the sequencer not even with 20%.

So my questions  ....

a) Why do these things go so bad???  Is it the way this box was stored? just plain age?? did something 'happen' to the box (electrical surge, damp conditions.....) that made these things so bad?? 

b) Is this just a foretelling of what I am going to find in the black and grey boxes???  With the rest of the unit so out of whack, are these likely to be bad also or will they 'just work'??

I will say my soldering (and DEsoldering skills) have improved dramatically with this project ;-)   I cant wait to get to the chaser lights! :-O

Thanks
Andy

[Ron Rich]

Hi Andy
What "parts list" are you using on the DCC ? Other then in the 2 minus voltages, that thing is not critical in any way. Which DCC 311125 board is installed--they made that board for over 10 years-- Many "substitutions" were used, from time to time, but I doubt I have changed more then 3 resistors per board to get the voltage readings within spec.
On the Sequencer-- very tolerant of out of spec resistors--the 2 watters on the board tended to drift --a lot, and were too hot as soldered to the board. When replacing them, I stand them off the board !
Some brands of resistors just age poorly, others are poor from the get-go ?
My advice on the sealed boxes--LEAVE them alone--If working, Do NOT attempt to "fix it" , as just the act of opening them, CAN, and has destroyed them !! Ron Rich

[andylevine]

Ron,

Parts list is the AMR Seeburg manual for the STD and FC series Electronic Units. That, and just the color coded bands on the resistors told me what the resistors SHOULD be.

The board in the DCC is a 311125-D. I wasn't testing voltages (yet) just testing to see if the resistors were even close to documented tolerances.

The sequencer I know has had some issues. I see smoke (flame??) marks where the smaller 10mfd capacitor sits. It and the other 3000mfd have been swapped out by previous owner but also show signs of heat damage. I am going to replace both of those as well. I did notice when the box was still all together that one of the strings of chasers didn't flash, just stayed solid. I assume thats one of the small NPN transistors on the board or on the chassis?? Is there a decent way to test these with limited equipment or do I save myself the hassle and just replace them all??

I'll take your advice and leave the black/grey boxes alone ;-)

Thanks
Andy

[Ron Rich]

Hi Andy,
Do you have a copy of my "MicroLog trouble shooting guide--If so look at the DCC notes--I don't know what the AMR re-print manual covered --but a lot of changes were made between the FC and STD series DCC's. Look at the diode on the sequencer-- If it has a brown colored marker, CHANGE it !
Smoke damage-- often-- also the IC dies once in awhile, and the resistors soldered to the ground strip, came un-soldered on some units. Small transistors are usually OK--but you can change them all real cheap--not critical at all--Ron Rich

[andylevine]

The AMR reprints have the Issue 3 schematic and parts list, same as your (quite excellent) MicroLog trouble shooter. Thanks for the heads up re: the sequencer diode. If you are referring to CR3, mine does have 'the brown band'. I'll replace it. Parts list calls for 100PIV, 1A, this still correct?? All the other diodes are tiny little things.

Andy

[Ron Rich]

Hi Andy,
Cool--should be OK--
I use a 1N4004, or better, as that's what I have--the small signal diodes are 1N914's or equal--seldom are bad ! Ron Rich