In between doing the several coats of primer on the Q*bert I'm not wasting any time...
So I fixed yet another 6100
This was a tough cookie. It was delivered with the simple yet very exact problem description: No Image
I had no reason to not trust the owner about that so I didn't even hook it up before "doing the basics".
I really don't like working on dirty stuff so the first job was to clean everything. Used paper towel and some mild cleaning stuff for chassis and tube, the boards were removed from the chassis and thrown in water and washing detergent in the kitchen sink and gave them a good cleaning with a brush
once clean they were dried directly in the oven at a comfy 50 degree, with the fan on of course
Then the basic stuff like testing all transistors and diodes, replacing all mica's and thermal grease on the chassis transistors (and finding out that two were not mounted correctly, which causes them to not be able to transfer their heat into the chassis metal......), resoldering all connectors, checking fuses, measuring all caps etc. etc.
I found out that apart from 1 or 2 caps on the HV board, ALL the caps on it were bad ! One of them was a Nichicon and that's the first bad Nichicon I've found ! The ESR was still OK but the capacitance on the low side...since I don't want the owner to have another problem in the (near) future I replaced all caps on the monitor by Panasonic 150 degree one's.
With the DVM on my multimeter I could not find any bad diodes or transistors so now it was time to hook it up.
No picture but I did hear HV and deflection chatter.
Measured B+ and it was way too low at 100V. Adjusted the HV pot but I couldn't get it any higher than 110V. Replaced ZD902 and bingo, B+ is back to 180V.
This shows that you cannot test a Zenerdiode with a DVM (well unless it's shorted or open).
I now kinda expected to get at least something on screen but apart from some very faint glare when I turned up the screen pot there was nothing.....I also smelled some heating up electronics, not unusual but I "fingered around" anyway and noticed that one of the huge resistors and one of the chassis transistors really heated up badly and quickly......mmmmm, are we sure all transistors and diodes are OK ?
Measured all of them again, no problem to be found.
So I swapped in the (known working) deflection board of the 6100 in my Gravitar.....and there it is, working !
So it must be Somehting on the deflection board for sure....
Decided to "shotgun" it by comparing every part in that section.....and I found one resistor to be into the mega ohms while it should be only 3.3 Ohms....replaced it and bingo, we have a picture !
Still need to do convergence but otherwise it's ready to go home.......but there is yet another 6100 waiting for its turn
In theory that one should be a bit easier.....we'll see but it's getting the total overhaul anyway
Here's a list of what I did on this one:
REPAIR LOGS:
Neckboard: P323
cap replaced
bent focus pin, focus was going bad when heating up
HV Board: P316
Bad caps ! => C901,902,909,914 - Replaced ALL caps on HV board
Bad connection on focus pot, fixed
Q906 mica insulator replaced, cleaned of old and dry thermal grease and applied new
replaced R918 pot
replaced ZD902, was bad (had low B+, only 110V)
Deflection board: P327
LV2000 installed
replaced F700,was 4A should be, and is 3A now
resoldered all connector headers
replaced all tantalum caps C800,801,802,803 with 1uF electrolytic
resoldered posistor, was loose
all other caps checked and OK
all diodes and transistors checked and OK
replaced R612 was bad (no picture, just some "glow" when turning up screen pot, power transistor heating up quickly and badly)
