Restoring a Microbee 32IC (WIP)

[amy]

So I started work on Dad's old 32IC. I can get 5V out of the 7805 on the core board, but the ones on the motherboard (under the keyboard) are dead. I've replaced D14 and the electrolytic cap, but I'm not sure if I can get at the 7805s without taking the keyboard off. Also when I desoldered them a couple of the solder pads lifted off the motherboard. Is there a way to re-solder the regulators without taking the keyboard off? 

I ordered some switch-mode replacements for the voltage regulators but I was wondering, if I have to take the keyboard off is it worth waiting for a new keyboard replacement kit?

[ChickenMan]

The keyboard replacement kit includes 2 switch mode voltage regulators also and I'd be 99% sure the current keys will need replacing also, so personally I'd pre-order one and wait for them to be available.

But in the mean time you will need to drill out the pop-rivet that holds the voltage regulators and then its a matter of how well you can handle the tight fit to remove the regulators and put in the switch mode regulators you have on order. Since these new ones need no heat sink, you may be able to re-fit them under the motherboard.

[someone]

So I started work on Dad's old 32IC. I can get 5V out of the 7805 on the core board, but the ones on the motherboard (under the keyboard) are dead. I've replaced D14 and the electrolytic cap, but I'm not sure if I can get at the 7805s without taking the keyboard off. Also when I desoldered them a couple of the solder pads lifted off the motherboard. Is there a way to re-solder the regulators without taking the keyboard off? 

I ordered some switch-mode replacements for the voltage regulators but I was wondering, if I have to take the keyboard off is it worth waiting for a new keyboard replacement kit?

Lifting PCB pads? It sounds like you're using a vacuum pump desoldering tool, too much heat both.  If you are, stop right now.
The regulators are easily removed without the need to remove the keyboard bracket.
Affordable and acceptable desoldering stations are available. After a bit of practise, components can be easily removed without any tugging whatsoever.

As as side note, why is it everyone's fascination with TO-220 switchmode voltage regulator replacements? Someone just uses bog standard linear ones.
If you're worried about the heat being dissipated, then run the bee from a lower voltage.  Use LDO versions if you want to run from even lower voltages but this may require adjustment to the voltage good sensing resistor network resistors.

[MbeeTech]

.. If you are, stop right now.

Someone has some very good points, but this may have come over a bit strong and I'm sure that was not the intention.

Lifting pads does usually mean too much heat, or heat applied too long.
Motorised vacuum desoldering stations are great & well worth the investment if you are doing repairs on a regular basis, but some people can't justify
the expense.  Manual vacuum desoldering tools are o.k. but care needs to be taken with heat as mentioned and this is the same with desoldering
stations as well.  The drawback of the manual vacuum desoldering pump is that you have to get the iron and tip of the pump over the joint you are trying to 
desolder close enough to get an effective vacuum draw of the molten solder.  This can lead to pressure on the tracks from the iron, especially when the 'recoil' 
of the pumps internal spring is triggered.

When repairing circuits with delicate tracks, it is far easier and kinder to the board to cut the pins of a device (usually as close to the component body
as possible) with fine sharp cutters and take the remainder of each pin out one by one with tweezers and the soldering iron.
Then once all pins have been removed, you can clean up the pads / holes by applying a little fresh solder and using the vacuum desoldering tool
of your preference. Desoldering braid is never a good idea for this purpose.

[someone]

Here's a budget desoldering station that at some microbee owners own:

$72 (On special but out of stock) 80W Desoldering Station | Jaycar Electronics
$155 ((delivered) back in stock July 22) MP740415 UK - Multicomp Pro - DESOLDERING REWORK STATION, 240V, 90W/UK (element14.com)
$185 ((delivered) in stock) MP740415 EU - Multicomp Pro - Desoldering Rework Station with Stand, 220V AC to 240V AC 50Hz, 90W (element14.com)

It's in budget and excellent occasional use.

[amy]

Thanks I do have a Rhino Tools desoldering station ( https://rhinotools.com.au/product/desoldering-station/ ) but I haven't quite mastered its use. I had it set at 290C and I was probably being a bit too impatient/aggressive with the desoldering, or the board was a bit more fragile that I thought. All part of the learning curve, I guess. I don't use the solder sucker any more because I know of its pad-lifting tendencies, and I've never had any luck with desoldering braid. I'll definitely try clipping the pins next time; I hadn't thought of doing it that way . I'm still not very good with all this stuff.

The pads that lifted from the motherboard were on the 7805, so I might have to get the keyboard off to desolder it properly? At least then I'll have it prepared for the replacement kit Is it worth trying to repair the broken pads? I've used copper eyelets on homemade PCBs in the past, though I heard some people use copper foil and epoxy. Or is that just kind of an aesthetic thing?

[someone]

Excellent Amy!
With the proper technique with a good desoldering iron one components can be removed unscathed (and be reused if not faulty).

Seemingly being counter intuitive, one needs to add additional solder to the joints to be desoldered;
Intuitively, hold the PCB so the solder holes are horizontal so the suction of the desolderer doesn't have to to fight gravity.
Don't be overly keen to pressing and releasing the trigger.
It's important not to release the trigger prematurely to prevent solder from getting stuck in the desoldering tool's barrel.

0. Install the correctly sized tip.
1. If you can apply a bit of flux paste to the joint.
2. Ensure there is enough solder on the solder joint. Add more if required using the desoldering iron for the soldering.
3. Heat the joint, when the solder has melted start wiggling (in sympathy of the component leads bends) the solder tip gently so the component lead moves in unison with the tip.
4. Keep wiggling, press the trigger and keep wiggling. This is where the solder is removed from the joint.
5. When satisfied that the solder is removed, keep pressing the trigger, stop wiggling and remove the tip from the joint.
6. Wait a sec and then release the trigger.

Sometimes the after the desoldering the component lead reattaches to the PCB pad. This is called a sweat joint.
If this occurs, the use a pair of needles pliers and gently wiggle the component lead to break the joint.
It's with experience that you'll work out when you can do this or have to resolder the joint and desolder gain.

7. Double check that all of the leads have been released.
8. The component can be pulled out without any force.

9. When finished, before turning the iron off, tin the tip and don't wipe the solder off.
This bit of solder greatly extends tip life.

QED.

Notes: With that cheapie desoldering iron and its brethren.
a. Its case fan is often noisy - who really cares when it desolders well.
b. Its heating elements doesn't win any awards for heating up or thermal stability - who cares when when the iron's cheap.
c. It'll take a bit of experimentation to tune in the default optimal temperature setting.
There will be times that slight adjustments are needed to compensate for solder pads on large copper fills.