128K Analog board recap

[falen5]

Hello again folks.

I got a 128K Mac with a clicking analog board.

I sold this machine to a chap in Malaysia bout 6 years ago ( all the way from Ireland !! )

He got in touch a few months ago to say it was no longer working and there was a clicking coming from the machine - flyback i assumed and needing a full recap.

It got here yesterday and I took off the bucket , all looked intact and tried to fire it up with my 110v supply

no life , no clicking but a hissing sound from the flyback.

took out the analog board to realize ........ Someone else tried to fix it !!!

Asked the owner and he confirmed.

I had previously replaced C1 , the 3.9uF cap before I sold it.

Then I noticed some of the caps had been replaced with 'ChongX' caps !!!

Then noticed one of the chips had been reflowed or replaced

Then I saw cracks in the flyback casing , revealing the red wire windings

Ive ordered up both kits from console 5

I took some voltage readings before removing the analog board , 12 is at 7.2 , 5v is at 3.1

I have to wait for the kits to arrive.
I have a few concerns - that flyback is cracked all the way around. From reading this flyback is the oldest type they used and it is recommended to replace it. I have seen videos of ChongX caps being way off spec / exploding , thats why I never use them. Looks like transistor Q3 was removed.

What is transistor Q3 ? power regulator ?

This machine has been shipped half way round the planet - I want to restore this board so it will last the chap many years to come - so rekon I have to 1: change the flyback , 2: full recap , 3: test Q3 ?

 

[cj_reha]

You were brave to offer a warranty on a mostly-original compact!

Q3 is the horizontal output transistor and would be the first part to short if the flyback failed (which all signs point to). Definitely check it. Recap is also a good idea, take care to change the Rifa line filtering caps on the AC input side alongside the 'lytics. They are a very common failure point.

 

[falen5]

You were brave to offer a warranty on a mostly-original compact!

Q3 is the horizontal output transistor and would be the first part to short if the flyback failed (which all signs point to). Definitely check it. Recap is also a good idea, take care to change the Rifa line filtering caps on the AC input side alongside the 'lytics. They are a very common failure point.

Thanks for that cj

It is a week 13 built machine. The chap that bought it was using it all the time.

The board around Q3 is discolored - I dont know if this is normal - The transistor is riveted to the heatsink so it is either the original chip or he replaced it with another along with the heatsink.

I have never had to replace a flyback or test one. Ill start reading up on how to do it

Oh the joys of it !!!

 

[Callan]

Flyback is definetly gonna need to be replaced. They crack like that when the internal windings short. You can test it with a ringer(lopt tester), but I'm 99% sure it's done. If it's the 1% your gonna have to fill the crack with hv putty and find you another flyback because it's not gonna last long.

 

[falen5]

Thanks for that Callan

Ive read I can use one from a plus or an SE.
This machine is a 110 volt , would it make any difference if the flyback came from a 240 volt machine

starting to get that feeling what i thought was gonna be a straight forward recap wont be so straight forward.

 

[Callan]

The flyback is driven off of 12v (12f). There shouldn't be any difference between the 220v and the 110v analog board flyback. I would, however, verify the flybacks part #'s are the same. That or make sure the updated/different flyback is a compatible part for your analog board.

 

[cheesestraws]

What is transistor Q3 ? power regulator ?

Q3 is the horizontal output transistor. According to Thomas H. Lee's document, it's a BU406.

From reading this flyback is the oldest type they used and it is recommended to replace it.

That flyback looks pretty stuffed, yeah. And the earlier smaller flybacks are ... weedy. That looks like a replace job to me.

 

[falen5]

From some more reading I can use the analog board off a Mac plus on the 128K

Being designed after the original I would imagine it would be a better board compared to the original analog board.

Recap kits already ordered are for a 110 volt - They probably wont be the correct caps for a 240 volt board , and being in Ireland the only boards I see on ebay are all 240 volt

Still waiting for the owner to get back to me but it would seem replacing the original analog board with that of a mac plus would be the safest way to go

Any thoughts folks

cheers

 

[cheesestraws]

From some more reading I can use the analog board off a Mac plus on the 128K

You can, yup. And they're common enough and easy enough to get hold of that this is at the very least a good spare to have.

Being designed after the original I would imagine it would be a better board compared to the original analog board.

It's basically identical, at least the ones I have are.

 

[falen5]

Thanks cheese

Ill pass it all on to the guy that owns it - its his call

 

[falen5]

Finally got my hands of a replacement board for the 128K - least thats what I thought until I took it out of the packaging

I think its an analog board of a Mac Plus

The chap that sent it has no history on it - its just from a box of old boards he said.

Some components are missing / removed but I do have the original board

So i guess I need some help on identifying the board - will it work for a 128K mac - does the flyback look ok on it - should I restore this new parts board or use it to rebuild the original board

the original board is 110 volt - this board is 240 volt

i have never had to work on a flyback before folks so appreciate any and all advice on this one

 

[cheesestraws]

Plus and 512/128k boards are essentially identical. The differences you are noting are more likely the 240/120V difference, the 120V board does look quite different.

 

[falen5]

any advice on that flyback folks - does it 'look' ok

 

[cheesestraws]

I'd probably file that flyback under 'grotty but probably serviceable' but I'm far from an expert. I can't see any cracks in the housing, so hopefully it's still solid. FWIW the bigger and smaller flybacks on Plus/512/128 boards *are* interchangeable, so if you had one originally with the piddly little flyback, you could replace it with the bigger flyback, AFAIK. When you fire it up for the first time, keep an eye out for corona discharge, which is a purple glow which tells you in a roundabout way that it's stuffed.

Please for heaven's sake make sure you are careful with the voltages. if I remember correctly, some of those big capacitors on those boards don't have bleeder resistors, so if you plug it in to test it, make sure you discharge all the big caps before you touch anything.

 

[falen5]

Thanks for that Cheese - I wouldnt even test it on the bench -i put it back in the machine just to make sure I discharge it properly

i guess flyback is 12 volt in , regardless of board being 110 volt or 240 , so straight swap of flyback would be simplest , but the original board
was worked on by someone else , they appear to have removed/ replaced components , and did a partial recap with some cheap caps

i dont really want to work on that board because of the above - but this board i just got may have just as many problems - parts removed make it a parts board ..... there must be a reason for it

guess ill go for recapping the new board and transfer the missing components from the original board

if it does not work i can try swapping back to the original , swapping over the flyback and everything else that was taken

DO NOT like working on these old analog boards - no bleed resistor

 

[cheesestraws]

Also, the 240V board is 240V *only*. It will not work on 120. In theory, you can adapt it, but I've no idea how.

 

[falen5]

on the 240volt board it says "remove w12 for 240 volt ", " install w12 for 110 volt " ( something like that ) and then about the different fuses to use for either - must be able to do both - then again im in ireland - all the machines over here are 240 volt

the recap kit i ordered is 240 volt so its staying at 240

just waiting on the caps now - should be here soon