Circuit Boards

[John C.]

I'm getting phone calls about circuit boards that were built pre-computer control and software. This set of boards came out of a Komatsu PC200-3 that has been turned into a drill. They controlled all the drill functions with these two boards and this one wouldn't turn on and when I got it to turn on it wouldn't turn on the compressor. The bottom board is where the power supply enters and they are using a latching circuit to turn the drill functions on. The relays are obsolete and no longer sold so I bypassed the latching relay to get the power relay to close. I am a bit stumped though on figuring out how to get the air compressor function to come on.
I could use any information that anyone might like to share about circuit boards in general. I have another client with a PC128 with a swing boom having issues as well. It might help a bunch of us. I'll post more photos in a bit.

Thanks in advance.

 

[heymccall]

I is quite versed on the PC128UU (and the pc228uu).

 

[John C.]

The first photo showed the top board. Inputs go in there and the LED bulbs light up when the circuit is activated. It plugs into the bottom board on a row of mechanical pin connectors underneath.

Here is the bottom board. The power input is on the right bottom corner.

 

[John C.]

Here is a closer view with the latching relays circled and an arrow pointing at the power relay.



The three latching relays are obsolete and I can't find any information on them at all. No idea of the pin connection schematics. The relay to the left of the circle that says Axicom was bad when I put power to it and the one on the board is only half. I put two wires across the circuits above in case they have to power something. I checked the relay on the board when plugged in to power and it was always closed to those circuits. When I plugged it in last time I got a low voltage alarm and the air compressor wouldn't turn on. Everything else worked in manual modes.

 

[John C.]

Here is the bottom board turned upside down and you can see what I had to do to get the power relay to close.

 

[John C.]

heymcall, as far as the PC128UU goes, the machine has the articulated boom with the safety system installed. The owner took off the articulated boom and installed a standard boom. The machine is now stuck in slow mode. We have been trying to find out if there is a way to bypass those old potentiometers. So far no luck. I told him to reinstall them, put them in a place where the computer says it is OK and then weld the levers in place so they can move. Have you found another way around them?

 

[heymccall]

heymcall, as far as the PC128UU goes, the machine has the articulated boom with the safety system installed. The owner took off the articulated boom and installed a standard boom. The machine is now stuck in slow mode. We have been trying to find out if there is a way to bypass those old potentiometers. So far no luck. I told him to reinstall them, put them in a place where the computer says it is OK and then weld the levers in place so they can move. Have you found another way around them?

Other than a flashing lamp, can't you just leave the reset terminals together?

 

[John C.]

I’m not at the machine but the client didn’t find the terminals.

 

[heymccall]

The easiest choice would be to eliminate the manifold with the limit solenoids. Simply remove the manifold and put a union in every in/out place.

 

[BB64]

John,

FWIW, I'm an over-educated a-hole EE (specialized in analog electronics and power systems) that works in custom batteries and I frequently have to chase down old parts -- we still build some of the same parts we started with in 1986. Glad you have discrete components, especially through-hole, it is my kind of PCB!

Anyway, my gutcheck was to suspect that those are SPDT based on the pins used... wish I knew why I still remembered that! Pulled up the NTE relay cross reference guide on Source Research and G2Q-187P-V-24VDC crosses to R70-5D1-24 that is available from Allied Electronics, Newark, or Digi-Key for $3-ish each. (I'm not throwing in links so this doesn't look like a SPAM post -- send me a PM if you need links.)

I did track some original Omron relays down by googling "Omron G2Q-187P-V 24VDC"; there is a site called worldwayelec that claims to have 80 pieces and someplace in Germany called S.E. Components that claims to have 550, plus lots that show in China -- my guess is most of these will either fail to exist anymore or will cost a small fortune.

Good luck,
Mike the EE

 

[Birken Vogt]

I do this kind of work too but nothing to add, it has been covered from what I can see. Watching to see how it turns out. More to come in the future as this sort of equipment ages.

 

[John C.]

BB64, wow that is a lot to process. I also found those listings from a Google search and you are correct. They don’t exist when I checked. I’ll check on that cross referenced number tomorrow. No none would acknowledge anything existed for those anymore even to cross. Can you point me in a direction to find out how those are supposed to work? The boards have several of them besides these.

 

[Birken Vogt]

Here is a model with similar nomenclature:

https://www.newark.com/omron-electr...c12/relay-signal-spdt-125vac-60vdc/dp/65H4977
https://www.newark.com/omron-electr...c24/relay-signal-spdt-125vac-60vdc/dp/30C2400

Looks like a simple SPDT relay as far as I can see.

What I saw said the G5V is the recommended replacement.

https://datasheet.octopart.com/G2Q-184P-V-DC5-Omron-datasheet-61013872.pdf

 

[BB64]

John,

Birken Vogt's last link shows a schematic. Pins are numbered sequentially as if they all exist, so one to ten. One is the NC (Normally Closed), Two is one end of the coil, Five and Six are the wiper, Nine is the other end of the coil and Ten is the NO (Normally Open). When you energize the coil, the wiper goes from the NC to NO contact as long as power is held to the coil.

My first glance said that rectifier diode D96 is suspect due to the discoloration on CN7 and the lead wires, then either your soldering or something else fouled D93B and pulled a trace up. If I had it in my hands with nothing soldered, I probably would have checked the 5W resistors by the voltage regulators first (my experience is that vibration causes failures in the fine wires inside, hence why they are slopped down to the board). Can you get the part number off the X2A SPST relay - suspect it is a G2R-1A-24VDC but the reflections, glare and angle are tweaking my brain -- that'll help tell you what the fried trace leads to.

Overall, it looks like classic early IC design: most of the rows of diodes are 1N4005's, the regulators are 7812's, IC1-IC3 are 555 timers (an amazingly useful IC), IC4 is probably a diode bridge, PCI is an optocoupler, transistors are probably 2N3904's, and the trimpots look to all be glued to keep them set with lots of RTV holding any parts that might fail internally if allowed to wiggle independently on their leads.

Good luck,
Mike the EE

 

[Vetech63]

I'm putting BB64 in my quick find guide. I still see some of these types of boards in the older Gradall machines.

 

[John C.]

Birken Vogt, the trouble I'm having on the first two relay links is the size and pin spacings. The ones on the board are smaller. The G2E relay shows the electrical diagram that coincides with the relays on the board that I checked with an ohm meter. The one that I bypassed to get the power relay to work is partially shorted through somehow on 1 and 6. There is about 1 ohm of resistance between contact 1 and 6 when all the rest of the relays are open at those two connections.

BB64, you are correct about the burn mark on the resister diode. I was trying to check operation of the relay and touched the wrong place with live voltage and the diode smoked instantly. The current diode is a new one I obtained and soldered in place. It did burn the trace so I connected it from the underside of the board. When I first suspected the board was the problem I started by checking ohm meter readings of the components that were the same. The big problem was that relay in the middle was different that all the rest of the relays on 1 and 6. The discoloration on CN7 I believe is because the power connection on the spade is loose. I could be wrong about that. I'm going to do something about that before I try the board out again.

Maybe you both could educate me on the initials. What does SPDT stand for? I know an IC is an integrated circuit. What is a SPST relay. I'll look for it and get the info off it. You are correct that this is old. The machine itself by model type was built in the seventies. The suppliers that I talked to said those particular relays haven't been made in 40 years. I suppose the use of boards like this was to reduce the size of the controls. I have worked on stuff in the past that had a plywood board installed over the rear window of the cab with rows of automotive type relays. I would label them and when something didn't work, I just looked at the label over the relay. It was a lot quicker and easier to solve.

Thank you both for your information. It is greatly appreciated.

heymccall, I'll send you a PM with some questions about the PC128 machines.

 

[John C.]

You are correct about the part number on the X2 relay. It is G2R-1A-24.

 

[BB64]

John,

Sorry for the delay - work is a four letter word, plus had to deal with doctor visits for my wife and run to the body shop.

Anyway, engineers love acronyms... hope I can manage a passable geek to English translation.
SPST = Single Pole Single Throw -- think of this as a standard house switch, only operated remotely by energizing the coil. It can be either NC (Normally Closed) to make contact except when energized or NO (Normally Open) to only make contact when energized. A SPST switch has two connections, a SPST relay has at least four so you can connect the coil. As an example, a starter solenoid is essentially a NO SPST relay.
SPDT = Single Pole Double Throw -- think of this as a 3-way house switch. A SPDT switch has three connections, a SPDT relay has at least five. One contact is the common (I learned it as the wiper, also called the switch arm that gets acted upon by the coil), as well as the NO and NC contacts and coil.
DPST = Double Pole Single Throw -- essentially two SPST relays run by a single coil.
DPDT = Double Pole Double Throw -- likewise, two SPDT relays run by a single coil. It is only minor trickery to use these to reverse polarity. The bloody things continue into 3P, 4P and up (but only rarely).

Because I'm guessing you are wondering, I can only suspect that the common on these miniature relays runs to two pins for mechanical stability once installed. I racked my brain to see if I could tell where the traces were running, but I didn't get a chance to print enlarged photos so I could look at front and back and keep a pointer or frame of reference (switching pictures on computers still mess with me).

By the way, I appreciate your videos, they offer a lot of practical mechanical insight.

Hope that helped - wish you the best of luck,
Mike the EE

 

[John C.]

BB64, no problem on time to respond. Any new knowledge to me on any time frame is way better than what I had. Thanks for the explanation of the relays. There is a relay that had two sides with a coil in the middle and six pins on each side of the coil. I couldn't get a new one as again everyone said there was nothing comparable to it but they did have one that is half of what I had. I bought that and installed it and just jumped the two life traces on the other side. Now that I know a little of the terminology I'll know a little bit more of what to search for. I'll take a photo of that one and post it below.

I put the boards back in the machine yesterday and the relays worked the way they should? I got everything back working again except of the compressor and the dust recovery systems. I suspect the big relay I talked about above might be part of the problem but I'm also beginning to think that there are wiring harness problems in the back of the machine. If I can find a replacement for the big relay, I'll pull the boards again and take a photo of them with a bright light underneath. It would show the traces on both sides sides. That's how I was able to follow them.

Thank you for your kind comment on my videos. The channel is getting around 6,000 views a month now world wide and I need to make some more over the winter.

Again, thank you for sharing you knowledge and insights. I wish you the best and hope to keep hearing from in the future.

John C.

 

[BB64]

John,

That is a miserable 4PDT relay -- Mouser, Newark and Digi-Key show it as No Longer Available (NLA) and I couldn't find a quick cross, so my unpleasant suggestion would be find something like a RadioShack Experimenter Prototyping Board (276-170) that is DIP (Dual In-line Package) spaced along the centerline with bus bars on the edges and "roll your own" with two DPDT relays (or if whatever chip is driving it won't drive two coils, you may have to use a SPST with a real low coil current to pull in the other two). If the original relay can be cleanly and safely desoldered, I have been known to replace it on the board with a machined DIP socket and then use rails of machined pins or another socket to make my connections - that way, you can disconnect the pseudo-relay board if you need to diagnose it further. I don't have part numbers for the sockets and rails handy, but could dig them out if you need.

Good luck,
Mike the EE