Hakko 470, 471 de-soldering station repair and schematic

[floobydust]

Need schematic for Hakko 470, 471 vacuum desoldering station.
The 474, 475 might be the same PCB.

My unit keeps overheating, triac is ok.

Update: {see post below}
For clarity,
The 470, 471 uses AC induction motor and timed vacuum solenoid valve, control PCB B1045.
The 470B uses a brushed DC motor and no vacuum solenoid valve, control PCB B2443.

[macboy]

I've never found one. The best I found was a wiring diagram showing connections between the board and transformer, pump, heater, etc.  However, with just one simple single-sided board, reversing the schematic is just a matter of a little time and effort.

If you don't have the time to spare, I know of a local dealer that has a couple of 470 base units without guns, and I'm sure he'd be willing to part one out to send you just a PCB, with the remainder going to scrap (the whole thing will eventually go to scrap if it doesn't sell). Since you are also in Canada, shipping the whole unit probably wouldn't break the bank either. PM me if interested and I'd be happy to broker a deal.

[floobydust]

I drew a schematic for the Hakko B1045 temperature controller PCB including the base 470-2.

When I connect the heating element, I get full heat, sometimes it backs off but very hot, like thermal runaway.
When I connect the 6.6R dummy load I get full heat, can't control it.
When I connect a 200R dummy load, the TRIAC seems to stay off. I get nothing but a blip, no heat.

The gun has no temperature sensor, instead Hakko seems to be using resistance change in the heating element. I am using a 474 heating element because the 470 is obsolete, but same wattage so should be OK... but might be my problem.
Anyone have ideas how to troubleshoot this.

macboy, thanks for your note. I will try fix it but that NEC uPC1701 is an oddball IC.

[floobydust]

Update:

The station uses the heating element's resistance as a temperature sensor.

I'd upgraded to 809 gun (A1313 heater) a long time ago, as the old 802 gun (A1029 heater) are obsolete.

Heat gets stuck on when the heater resistance is lower (current higher) than expected. The newer element must have lower resistance. I just did a re-cal and the station behaves better. The controller can probably still go into thermal runaway if I crank up the temperature setpoint. Changing circuit values a bit too much work for now. Added an heater-on LED to keep an eye on it.

I did characterize the A1313 heating element. Resistance is 2.85ohms/25C and 8.36ohms 425C; linear slope. Higher tempco than nichrome wire.

These are the best desoldering stations I've used, even though old. Pace and Weller just don't work as well.