Early 90s Bowling Scorer Board - Page 1
Forum section: electronics / repair

author: RyanG
author_rank: Regular Contributor
timestamp: January 20, 2017, 01:27:50 am
content: Been lurking around the forums and watching all of the videos on YouTube for a while. I finally decided to post on here to ask for help with these boards that I have been attempting to get working for a while. This board goes in our scoring TVs at a bowling alley. It takes a black and white input over coax + color information from another computer to make the video for the grid to see your score while bowling. I know that just looking at the picture may not be enough to say what is wrong, but I thought someone might have an idea. I have tested all the electrolytic caps, all the BJTs(red dots are 3906 others are 3904), diodes, and resistors. I have swapped the MC68701S-1 with a known good board. Video comes into the board through the J2 connector, at the top left as black and white. The connector at the bottom left, J1, is an input from the main computer for color overlay and signalling the external relays to turn on some CRT monitors. The rest of the connectors are for AC input, outputs, or not used. The correct power is coming into the board. The DIP switch is for the assignment of the lane the board will be used on. This board, for example, is set for lane 12. The testing was done on lane 12. The +10v and -10v test points are good. The relay at the top right is good. The problem that I have is that the color output is almost completely blue. The output is RGB-Sync through the connector at the top center. That connector also provides VCR video output, which we no longer use. I have this same problem on quite a few of these boards and I have no idea where to go from here after testing most of the components. Schematics for the entire system are unavailable to anyone that I know of. I do not have an oscilloscope available at this time.

author: xrunner
author_rank: Super Contributor
timestamp: January 20, 2017, 01:48:43 am
content: Quote from: RyanG on January 20, 2017, 01:27:50 amMan, you really need a scope. But I find it very interesting that you say you have thesameproblem on "quite a few of these boards". That almost makes me believe that it isn't a problem on the boards ...The same problem - I mean it isn't impossible but are you sure it isn't the next system after the boards? But I have very little to base that on besides my gut instinct.

author: RyanG
author_rank: Regular Contributor
timestamp: January 20, 2017, 02:04:09 am
content: I have taken one of the few boards that we still had in box, and swapped it in place of one of these and it works perfectly. I have also tested one of these in place of one that is currently working correctly, and it turns all blue when I put one of these in. As for a scope, I have been trying to find a decent one on ebay.

author: xrunner
author_rank: Super Contributor
timestamp: January 20, 2017, 02:28:48 am
content: Quote from: RyanG on January 20, 2017, 02:04:09 amWelp - it appears then that you have a collection of boards with the exact same failure mode, and so that points to the same component(s). In a way that will help you find them as you have a comparison board that works and once you isolate whats wrong it should apply to all the failed boards.QuoteGood, there are LOTS of good used scopes on Ebay that are plenty good enough to use for this issue.

author: JoeO
author_rank: Frequent Contributor
timestamp: January 20, 2017, 04:13:23 am
content: Here is a link to Brunswick's service manuals. These may be too new for your equipment.I sent you an email here. Go look at it.http://www.brunswickbowling.com/service-support/tech-support/documentation/service-manuals/service-manuals-automatic-scoring/

author: RyanG
author_rank: Regular Contributor
timestamp: January 20, 2017, 04:44:49 am
content: Those are too new for the stuff we have. I have checked there and I have emailed Brunswick for the AS-90 schematics, which is a system they no longer support.

author: Cupcakus
author_rank: Contributor
timestamp: January 20, 2017, 07:51:55 am
content: I'm curious how you tested the transistors? Looking at the board those three pairs of transistors seem to run straight to the RGB signals on the output, that would be my first guess, should be a simple thing to change them out and see.

author: CJay
author_rank: Super Contributor
timestamp: January 20, 2017, 12:27:18 pm
content: I'm curious, is there any legible video on the screen when you connect a faulty board or does it just turn blue?I have a suspicion that the processor, the 68701, isn't running or coming out of reset so after checking voltages I'd test voltages to the CPU, pin 21 should have 5V.Pin 6 is the reset input, it's active low so if the pin has a low signal on it then it's in reset, if it's pulled up to VCC then the chip is free to run.Pin 2 and 3 are the clock crystal connections, it's possible that probing one pin with your multimeter would give you an indication if the clock is running, if it is I'd expect to see some indeterminate voltage on there, likely to be half VCC or lower but not zero, probing one pin will almost definitely make the clock stop, probing the other probably won't but you'd need to compare with another working board.Be VERY careful not to short anything out.

author: RyanG
author_rank: Regular Contributor
timestamp: January 20, 2017, 01:23:27 pm
content: All of the screen is readable. By default the background should actually be black and the foreground should be part white and part green. Instead with the bad boards the background is blue and all foreground is a dark blue that is almost black.Almost time for work now, so I'll check the voltages at the pins on a working board and one of the bad ones.

author: nali
author_rank: Frequent Contributor
timestamp: January 20, 2017, 02:24:17 pm
content: It sounds like there may be some DC clamping (not) going on with the Blue channel if the background is lifting.You've got 3 identical sets of video output stages top left, it should be pretty easy to trace out one of them, then find out the RGB path which I guess will come via one or more of those 4066s, then take it from there.

author: RyanG
author_rank: Regular Contributor
timestamp: January 20, 2017, 02:31:17 pm
content: The voltages all checked out fine. The screen is now more gray than blue and the foreground is black but very dim. I know the problem is in the board because another board in its place works. I will also try to trace out the rgb path.

author: RyanG
author_rank: Regular Contributor
timestamp: January 20, 2017, 02:45:15 pm
content: I read voltages at the RGB output pins on a working board compared to the not working and they are significantly different.

author: james_s
author_rank: Super Contributor
timestamp: January 23, 2017, 04:56:27 am
content: Work your way back from the RGB pins and see where they connect to. I suspect the 4066 chips are used to switch between the two video sources dynamically, that's how simple video overlay devices work. As the monitor is painting a line, the circuit will switch between different sources at precise times causing the graphic from one source to appear overlaid onto the video. A scope would be very useful here, but you'll also need to sit down with a pencil and paper and start drawing out the relevant portion of the schematic.If all else fails, you could try the shotgun approach and replace parts one at a time until you find the problem. Since you have a bunch of boards with the same issue that's a potentially viable approach. Whatever the case, let us know what happens, I love messing with stuff like this.

author: RyanG
author_rank: Regular Contributor
timestamp: January 23, 2017, 07:16:21 am
content: I am attempting to work on some of the schematic, but I guess I don't completely understand what the weak point in the system would be. I checked voltages at the base of each of the transistors while the board was installed and powered on, and they were no where near the voltages on a board that works correctly. I am assuming the transistors for the colors are fine based on checking them with a DMM with the diode test function while in circuit. But, since I don't know exactly how the BJTs are connected without a full schematic I suppose I can't be sure that I am getting good readings. Would a transistor be more likely to be bad than one of the 4066s?

author: nali
author_rank: Frequent Contributor
timestamp: January 23, 2017, 07:42:51 am
content: You don't need a full schematic to get an idea of what's going on, just trace the blue video as that seems to be the dodgy one to get an idea of what's happening. The red & green will be duplicates. As James says the video source is probably switched between different sources by the 4066s so possibly either one of those is faulty or the digital logic driving them so one of the switches is stuck.Also, it's not uncommon for video signals to be AC coupled in order to DC bias them, then clamped back to 0v at the output stage (0v = black). So if Blue wasn't clamped it may have a huge offset. Maxim have a tutorial on the subject herehttps://www.maximintegrated.com/en/app-notes/index.mvp/id/3303You really do need a scope...

author: RyanG
author_rank: Regular Contributor
timestamp: January 23, 2017, 08:35:10 am
content: I understand that each of the colors will be basically a duplicate. Will there be 2 4066s for each color? There are 6 on the board. I'm really not that good at this. Haven't been working on this stuff for very long. Been trying to help save money at work by doing more stuff like this myself rather than trying to send it out. And, now we have almost no choice but for me to attempt to fix these things. I can't really find anyone that services them. The only other thing I really know is that Zenith made these boards before LG bought them.I have traced some of this out. I'll type it here for anyone who wants to try to understand what I type. Each matching set of transistors, resistors, and capacitors at the top left of the board are for a color. The bottom most being for red, the next for green, and the top for blue. The PNP transistors' collectors are parallel to the left most 4066's pin 9 (SIG C OUT/IN). The PNP emitters then go to the base of each of the NPN. The NPN emitters parallel back to the compen pin on the MC1408-8N, and each also goes to its respective 75 ohm resistor through the relay to the output pin. As for the collectors of the NPNs, I haven't figured that out yet. 3:30 in the morning, bed time.

author: james_s
author_rank: Super Contributor
timestamp: January 23, 2017, 05:02:54 pm
content: I would suspect a 4066 before I'd suspect a transistor, I've seen them fail before in other stuff, they're older CMOS parts and are likely susceptible to ESD. Grab a datasheet so you understand how the part works, then use a logic probe or scope to check the control pins and see if they're toggling. You're going to need some sort of test equipment here, otherwise you're just guessing. If you can't get hold of a scope, at least buy a logic probe, they're less than 20 bucks. You should be able to find a scope for $50 or less too with some looking, you don't need anything fancy, a 20MHz analog scope would be fine for this sort of stuff.

author: edavid
author_rank: Super Contributor
timestamp: January 23, 2017, 05:59:04 pm
content: What do you see if you disconnect the blue video output?

author: RyanG
author_rank: Regular Contributor
timestamp: January 24, 2017, 06:24:12 am
content: Alright, I got a scope. I put the scope on many of the control pins of the 4066s and I don't really see anything useful on the scope. I am doing this at home with no video signal into the board, which probably makes the whole thing pointless. The power I am supplying it does go to all the ICs on the board, though. I'm starting to think that this is more trouble than it's worth because I don't know enough. I thought it might be somewhat of an easy fix.

author: james_s
author_rank: Super Contributor
timestamp: January 24, 2017, 06:36:33 am
content: Don't give up just yet. Stick at it for a bit, you're bound to learn something. Also I'd really like to know what the problem turns out to beYes it may depend on seeing a sync signal on one or more of the inputs in order to function, it's very likely that the video sync input drives an interrupt pin on the CPU, and from that the CPU knows where the beam is while drawing each line so it can switch the 4066's at precisely the right time.Do all of the defective boards produce a picture that looks blue? Have the failures been evenly distributed amongst the various displays or is there one or more units that seem to kill boards regularly?

author: RyanG
author_rank: Regular Contributor
timestamp: January 24, 2017, 06:55:19 am
content: I'm pretty sure that almost every failed board does almost the exact same thing. I tested them quite a while ago so I don't remember exactly what is wrong with them all. The failures are pretty random, although we haven't had too many lately.

author: james_s
author_rank: Super Contributor
timestamp: January 24, 2017, 04:57:46 pm
content: Well if you give up and have a spare board you can send me I'd be curious to take a look. Not having the rest of the system here I can't make any promises but I do have a digital IC tester and a good desoldering system that makes pulling soldered ICs a snap.

author: RyanG
author_rank: Regular Contributor
timestamp: January 24, 2017, 08:53:17 pm
content: If I unplug the blue output the screen is black, to answer that question. I'm back at work today so I got a chance to test that. I used the scope on several of the 4066s and again got nothing useful even with video input being applied to the board.

author: nali
author_rank: Frequent Contributor
timestamp: January 24, 2017, 09:44:55 pm
content: OK well first things first. Do you know how to interpret a video signal on the scope?Triggering might be a bit tricky, but you should see something like this on the scope:I'm going from memory as it's a loooong time since I worked on video, but the above represents a horizontal line and should be at 15kHz-ish. The levels at the front/back porch should be ~0v which represents black or rather no colour for that channel. The negative going pulses are the sync and the waveform in between is the actual video. 0v=dark 700mV=max. (forget the color burst, that's for composite not RGB)The 4066s will be for switching the video between sources so check them, and the digital switching signals on pins 5,6,12,13. One of the 4066 switches may also switch the video signal to 0v during the front or back porch, this is to ensure that "dark" is actually 0v and is what I was referring to earlier by DC clamping.At least you have working boards to compare against which should make life a bit simpler!

author: RyanG
author_rank: Regular Contributor
timestamp: January 25, 2017, 12:08:46 am
content: On a known good board I get something readable on all 3 color output pins, but the bad board gives basically nothing on the same pins. Forgot another probe at home.Pictures

author: james_s
author_rank: Super Contributor
timestamp: January 25, 2017, 01:28:22 am
content: Quote from: nali on January 24, 2017, 09:44:55 pmWhat you show is a composite video signal, that won't be the case here because this is RGB. I've only worked on the monitors used in these systems because they're also used in arcade game cabinets but they use analog RGB that is typically 4V full on, 1V black, 0.8V blank and then TTL level sync which can be separate H-V or composite sync.Look at the pins on each side of one of the switch elements in a 4066 and compare to the same points on a working board. Do this test in-system.

author: RyanG
author_rank: Regular Contributor
timestamp: January 26, 2017, 07:02:09 pm
content: I've tried reading off the 4066s with no real luck. I only had that scope temporarily, so that's gone. Kind of stuck going nowhere now. I have enough spares to last a while hopefully

author: james_s
author_rank: Super Contributor
timestamp: January 26, 2017, 07:31:32 pm
content: What did you see? Are the control inputs toggling? A logic probe would be helpful here, they're cheap.

author: RyanG
author_rank: Regular Contributor
timestamp: January 26, 2017, 10:18:38 pm
content: I didn't see much of anything happening on the scope besides the difference on the video output pins

author: james_s
author_rank: Super Contributor
timestamp: January 27, 2017, 12:09:56 am
content: Is the CPU running? Take a look at the Reset pin with a logic probe, a DMM will work in a pinch. If that's not in reset state have a peek at the address bus and see if it's doing anything.

author: RyanG
author_rank: Regular Contributor
timestamp: January 27, 2017, 01:26:56 am
content: I'm pretty sure when I checked the reset pin before it was at 5v on both the good and bad boards.

author: james_s
author_rank: Super Contributor
timestamp: January 27, 2017, 01:48:51 am
content: Next thing to check is the address and data bus lines for activity. Keep in mind this may have to be done with the board operating in the equipment.

author: RyanG
author_rank: Regular Contributor
timestamp: February 09, 2017, 03:55:32 am
content: Haven't replied in a little while, but I have had no luck with these boards. I am also working on a bunch of other electronics related projects as well as my normal mechanical stuff. Thanks for the help you guys have given.

author: Cupcakus
author_rank: Contributor
timestamp: February 10, 2017, 07:03:08 am
content: It's too bad no one on the board

author: Cupcakus
author_rank: Contributor
timestamp: February 10, 2017, 07:04:48 am
content: It's too bad no one on the boards is close enough to you to render aid, with just a bit more test equipment and know how I'm sure this could be tracked down.

author: james_s
author_rank: Super Contributor
timestamp: February 10, 2017, 07:17:31 am
content: Well I offered to take a look at one for the cost of postage.