Nieman 3M27SF / Rodotron 666 problem

vizzinni

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I could use some help troubleshooting this monitor. I think it's some sort of horizontal circuit problem, but I'm not sure.

Rather than trying to describe it, I've posted a video on YouTube: https://youtu.be/cJ4ZUrg0ATA. It starts out OK but within 45 sec or so things start to go wrong, and by 2:00 it's settled.

It's been working fine, at least in 15k mode, since I installed it in an empty Golden Tee cab. It's connected to a Pandora's Box 4 through the JAMMA harness (since I couldn't get it working in VGA/31k mode). It's also been hooked up with a World Class Bowling PCB and worked fine. Switching between the two required some minor tweaks to the Horiz settings on the chassis, but otherwise no problems.

Probably got 10 good hours of use before it started acting up. I'd left it on for several hours after leaving the house for a while and when I got back it was all screwy, and it hasn't been right since.

The problem seen in the video is about the same in both 15k and 31k modes, although in 31k it's bad right from the start, while in 15k mode it starts out OK then goes bad within a minute.

At about the 1:55 mark in the video I adjusted the H POS pot a bit which seemed to bring the picture back, but only for a few seconds.

I just installed a cap kit hoping it would solve this. There's 4 caps I couldn't replace because they didn't come in the kit (C55 on the main PCB, and C201, 219, 220 on the neck board).

The B+ at R33 is 69vdc. I don't know which model of board I've got so I'm not exactly sure what the setting should be, however, I couldn't adjust it lower than 64vdc or above 70vdc for some reason.

I also replaced the H POS pot.

I installed a 12v fan blowing over the neck board and it seems to keep things fairly cool so I don't think it's an overheating problem.

I know I could reach out to Rick at Nieman Displays but I thought I'd try here first.

There's a couple different schematics out there, I've attached the one that seems to match my setup.

Any ideas?
 

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  • Rodotron_CH-666_Schematic.pdf
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what i do not understand is "70v" ?
also u have a impedance s/w on that chassic
are u aware of that ?

ed
 
Thanks for the reply Ed. 70vdc is the B+ reading when I've adjusted the pot all the way to the right, although I tried again later and it maxed out at about 74vdc. And yes, I'm aware of the impedance switch; it's set to 1k when trying 15k and on 75 when trying VGA.
 
ya i was looking it over
the b+ should be 135-150vdc
170v is the pass feed through or for tech term post requlation
plus to confim it u have a 250v cap in the b+ circuit

ed
 
The specs I have for the Rodotron 666 is that when in 15k mode the B+ ranges from 55v to 75.5v, depending on whether it's a 666A, B, or C version.

The 31k ranges are from 100v to 140v. I'm assuming my board is a 666A given the adjustment ranges I'm seeing, in which case the B+ at 15k should be 75.5v and at 31k should be 140v. I measured my 31k B+ at 140v, so that's good.

I maxed out the 15k B+ adjustment to 74.4v, but it made no difference in what the monitor is doing.

I verified that the nearest cap to the B+15k pot (C23) is 250v.
 
ya u had better give rick a call
i have never heard of "main b+" like that ?
now the sub b+ i see i can understand
but never the main..or how can it substain ?

ed
 
For continuity's sake, I thought I'd keep the thread going until this is fixed.

Traded emails with Rick, he recommended checking C84 and if that doesn't do it, replace IC9.

C84 is supposed to be 115J/250v MPS (1.1uf 5% tolerance), which is surprisingly hard to find. A 824J/250v MPP had been installed. While I was poking around I looked at C85 which is supposed to be 103J/2kv PPS; what was installed was a 912J/2k PPS. These are close to specs but maybe not close enough?

I'll update when I've replaced these caps with the right ones.
 
FYI...I got a new IC9 from Rick and that appears to have solved my original problem. But now I have several others that I didn't have before.

Looks like one of the video transistors is shot; the display was all red at first then I swapped a couple of the transistors and the now there's no green. I'll order the transistor. Also, I've handled this delicate chassis so much probably causing more bad solder joints, and pulled off a few pads and traces because they're so damned delicate ( or my poor soldering skills). It's also a bit jittery, and the scanlines on the top 1/6th or so of the screen are much thinner than the rest of the display. So looks like I'll just try to suck all the old solder off and reflow w/ 60/40, replace the video transistor, and go from there.
 
@vizzinni ^^ I have a 3M25SF with this exact problem (although I would say mine is "very" jittery). Did you ever get this figured out?

FYI, that user's account says he hasn't logged in since Jan 30, 2022. So he might not see your post. You might want to leave a comment on the youtube video in the OP, as another way to try to reach him.

Interesting necrobump though. I've never heard of this monitor before.
 
FYI, I got an email reply from Rick Nieman ([email protected]):

"This is most likely caused by one of the 2 standup boards. IC5 or IC9. IC5 detects the frequency and selects the B+ accordingly. IC9 is the sync seperator."

Now trying to see if I can buy those parts from him. Will update here with any progress.
 
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Amazing that you can just reach out to the owner of the company, and he'll help you out. (I did go digging and found another thread where Ken Layton said the same.) Good to know that resource is an option. Thanks for posting!
 
Update 2 - Heard back from Rick about purchase of IC5 and IC9 replacement parts:

"$60 each or $100 for 1 of each plus post. Payment would be Western Union or Paypal"

I'm probably going to see if I can find a donor chassis first to help figure out which IC is bad. And I'll try replacing all the caps before I buy anything.
 
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