Please help in saving this WORKING power supply - Page 1
Forum section: electronics / repair

author: administr4tor
author_rank: Contributor
timestamp: December 06, 2022, 11:30:47 pm
content: Hello,I have an old furnace in house and this is itsworking control module.How can I collect information/date/readings/measurements from this working module so in case if something happens to this working module I can cross check from the information noted down and find broken component easily.Should I take diode mode measurements of all the soldered pins on theGREEN SIDE OF THE board?Any other ideas?I am not too good electronics troubleshootingthankyou

author: fzabkar
author_rank: Super Contributor
timestamp: December 07, 2022, 12:40:56 am
content: If it were my device, I would trace the circuit.The coil would be some kind of custom wound ignition coil. Thyristor THY1 would be the ignition switch.The IC is made by Hitachi, but I can't find any information about it. I'm thinking it may be a custom uC, possibly 4-bit or 8-bit, but I can't remember if there was anything of this kind way back in 1975 (assuming 7518 is week 18 of 1975). I can't see a crystal, so that makes me think I'm wrong.I see references to an NEC uPC3605CA, but this turns out to be a 3-terminal regulator. :-?

author: james_s
author_rank: Super Contributor
timestamp: December 07, 2022, 01:06:07 am
content: I wouldn't mess with it, if it does fail some day it's probably going to be fairly easy to troubleshoot, usually the issue is bad solder joints, bad capacitors and occasionally a bad relay.That looks very old though, what kind of furnace is it? Personally if it's more than about 15 years old I'd just replace the whole furnace if it fails. Last year I put a new furnace in my brother's house, the old one was only 70% efficient, the new one is 98% efficient and has a much quieter variable speed blower and modulating burner, it's a vast improvement.

author: administr4tor
author_rank: Contributor
timestamp: December 07, 2022, 02:29:00 am
content: yes, its an old furnance and old house, I dont want to spend too much money for furnace now, I am ok with 70% efficiency until it fails. As cost of new furnace is insane now a days. I have upcoming expenses for roof next year

author: administr4tor
author_rank: Contributor
timestamp: December 07, 2022, 02:29:40 am
content: Quote from: fzabkar on December 07, 2022, 12:40:56 amhow do I trace the circuit? I dont know how to trace it. can you help me?

author: Black Phoenix
author_rank: Super Contributor
timestamp: December 07, 2022, 02:50:25 am
content: Quote from: administr4tor on December 07, 2022, 02:29:40 amWhen he says trace the circuit means picking up a pencil and paper and drawing where each component is and to where it connects.You can follow the connections by reading the traces on the PCB or using a DMM in continuity mode and probe component legs to confirm if they are connected between them or not.More about it:https://youtu.be/wkAp5x3Z_gc

author: GigaJoe
author_rank: Frequent Contributor
timestamp: December 07, 2022, 03:09:22 am
content: frankly , it uselessat first , chip are basic custom logic to manage furnace, it not a power supply at all ...it turn exhaust motor, if existit manage gas valve on/offignite itusing a sensor to verify flameturn on air motorand do in opposite sequence if unit shut downdue to chip unavailability , the whole board non reparable at alleverything you can do to find same , or similar board. you need to know what each pin responsible for and with some luck find a similarfor example: pin "sensor" most likely flame sensor, diff board and sensor may be not compatible.would be a very cool ka-boom if timing to open gas valve and ignition will shifted by differ board. But it your house anyway

author: administr4tor
author_rank: Contributor
timestamp: December 07, 2022, 04:49:19 am
content: Quote from: GigaJoe on December 07, 2022, 03:09:22 amyes, if chip dies end of story, its getting thrown but how do we know if chip is not dead? Take diode mode measurements of chip legs? so if chip dies we know right away and dont troubleshoot remaining board?

author: GigaJoe
author_rank: Frequent Contributor
timestamp: December 07, 2022, 05:13:26 am
content: to know if chip NOT malfunctioned you need a detail description how it work , sequence of signals, then compare with actual work.at least what you can do with multimeter to make a detail schematic and layer of voltage map, when furnace working , so late you can compare.

author: james_s
author_rank: Super Contributor
timestamp: December 07, 2022, 05:20:59 am
content: Quote from: administr4tor on December 07, 2022, 02:29:00 amI haven't looked lately but a year ago I paid $2100 retail for a top of the line 60k BTU variable speed modulating furnace, with what natural gas costs these days the payback time is not too bad. Of course if you pay a HVAC company to come out and install it they charge a fortune but it's not all that difficult.As far as repairing that one if it fails, the electrolytic capacitors are the part I'd most expect to fail, one of them looks like it's gotten pretty hot, I suspect that's a zener diode next to it.

author: J-R
author_rank: Super Contributor
timestamp: December 07, 2022, 07:45:41 am
content: Find the controller part number and buy a spare on ebay?

author: administr4tor
author_rank: Contributor
timestamp: December 07, 2022, 03:12:02 pm
content: Quote from: GigaJoe on December 07, 2022, 05:13:26 amOn which pins should I take these readings?

author: coromonadalix
author_rank: Super Contributor
timestamp: December 07, 2022, 03:27:08 pm
content: First i would say this board heat a lot seeing all the burned spots on the pcbI would add more ventilation with holes in the casingCapacitors should be serviced or checked .... mostly the small ones around the icCheck the parts solders for cold joints, cracked soldersIt will fail sooner or laterThe coil seem's to be the igniter IE high voltage pulse outputs ??And the question about monitoring this device :Without a schematic, i would not even try any external device additions or modifications or sensors ... i would need to probe many spots, one misshap and you could blow a part or create some problemsMostly due to ac lines going into it too...and finally your sentence: I am not too good electronics troubleshootingGet or find a spare in case of ...Furnace brand / model, and the pcb green side markings you have some who may tell the model ending with 37FSeems an old Hitachi logo ??

author: james_s
author_rank: Super Contributor
timestamp: December 07, 2022, 06:50:58 pm
content: Quote from: administr4tor on December 07, 2022, 03:12:02 pmFrankly even with experience reverse engineering things I would not attempt to take voltage readings off he IC. All it takes is a slip of the probe tip to short something out and release the magic smoke. You could easily damage the board beyond economical repair by attempting to do this.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: December 07, 2022, 07:56:25 pm
content: " slip of the probe "so true , better use a sharp needle like probes, with isolated ends

author: fzabkar
author_rank: Super Contributor
timestamp: December 07, 2022, 09:37:34 pm
content: What is the model number of the furnace? I notice that there is a 24VDC input, but both relays are rated for 12V. This seems odd. :-?

author: administr4tor
author_rank: Contributor
timestamp: December 08, 2022, 04:58:34 am
content: This is the model number of FurnaceLennox Furnace Model G14Q3-60-13https://www.repairclinic.com/ProductDetail/1236445https://www.completeheating.ca/images/pdf/LennoxG14.pdf

author: james_s
author_rank: Super Contributor
timestamp: December 08, 2022, 05:09:30 am
content: Oh that's a Lennox Pulse, I haven't seen one of those in years. Those are actually super cool, they're essentially a pulsejet engine, completely different design than any other furnace out there. They're one of the first 90%+ efficiency furnace, IIRC some are prone to cracked combustion chambers and I don't think you can get the leaf valves for them anymore but if it's working you may as well keep it going.

author: administr4tor
author_rank: Contributor
timestamp: December 08, 2022, 05:14:24 am
content: Quote from: james_s on December 08, 2022, 05:09:30 amYes, its has not leaked carbon monoxide yet because of known crack issue, I have put 4 carbon monoxide detectors around it.so I want to save the board of this furnace as much as i can

author: coromonadalix
author_rank: Super Contributor
timestamp: December 08, 2022, 12:56:09 pm
content: Well i gave you some tips, change the capacitors for a start with 105 degree ones, sames values for voltages and capacityCheck the solders on the board as i wrote earlier it could have some defects on them, mostly the big parts who heat a lotVenting the board would help cooling itOnce again without no schematics i would not play in it, when or if it become defective you will know fast enoughTry to get a spare part, this one seem old enough to became rare on the electronic side of thingsattached document for some wirings and tipsYes its not what you want to hear BUT you need something to work on before doing any attempts who could result in a dire situation if you do not have a backup planSearched tons of websites for the IC, never found itsome references for near number match but not the good one, it could have been a custom part in the past

author: Jetecnet
author_rank: Contributor
timestamp: December 08, 2022, 01:43:25 pm
content: There's one module on Ebayhttps://www.ebay.com/itm/285059921681JC

author: administr4tor
author_rank: Contributor
timestamp: December 08, 2022, 02:00:17 pm
content: you all are AWESOME

author: coromonadalix
author_rank: Super Contributor
timestamp: December 09, 2022, 07:50:01 am
content: Where you the buyer loll