Compact Mac CRT compatibility

[Concorde1993]

Hello:

This is my first post on the 68k forum. I own three compact Macs (a 1986 512ke, which was upgraded to a 1987 Plus, a 1988 Plus, and a 1988 Mac SE (SuperDrive Model)). The 512ke works perfectly, after several of the analog board capacitors were replaced by a TV technician. The SE, which has been in the family for over 17 years, works as well, however the CRT, after many years of heavy operation, has severe screen-burn (I can post a picture as soon as I receive a reply). The 88 Plus has a faulty analog board (wavy-line syndrome on the CRT). I can get the board repaired for just under $100.00, however I would prefer to put the money towards an SE/30, or a Portable (if I can find one).

To make a long story short, I brought in my SE & Plus to the same TV technician who repaired the 512ke. The concept was to exchange the CRT from the Plus with the CRT in the SE (which has the screen-burn). The following morning, I received a phone call from the technician, who stated that the Plus display was incompatible (the voltage on the Plus was rated at 30, whereas the voltage on the SE was 400).

One would figure that both CRTs would be compatible, since they were both made by the same manufacturer (Clinton), and in the same year (1988). I have already posted a want ad on Kijiji for a donor SE, but so far no success.

Any suggestions as to why these CRTs are incompatible? I know for a fact that the Classic & Classic II monitors are incompatible with the earlier compacts (128k-SE/30).

Naturally, any help would be greatly appreciated. Cheers.

 

[Paralel]

$100 to repair the analog board? That seems rather pricey.

 

[Concorde1993]

Well, the caps alone for the board are about $20 a pop (for the 870 volt type) plus labour. The benefit is at least I receive a warranty for the work done on the board. If something goes wrong, I simply bring back the unit.

 

[LCGuy]

They should be interchangeable, have a look at Scott's thread on CRT interchangeability.

 

[Concorde1993]

Hello LC Guy:

Thanks for the response.

I looked at Scott's thread just before I joined the 68k forum. In theory, these monitors should be compatible, however, the technician I spoke to said that they are not due to a difference in voltage rating (the SE CRT is higher than the Plus CRT). In order for both to be interchangeable, the voltages must be exactly the same, in order not to overload the analog board/power supply.

Naturally, I do not want to cause any damage to the SE (I have never had any problems with it; it's a very reliable computer), and I trust the expertise of the technician I am dealing with (he has been servicing TVs for over 40 years).

The only thing I can think of is that the analog board in my SE is not a stock SE board, but rather a Classic, or Classic II board (the SE was purchased used in March 1992). Either way, if I do not have any success with the forums, I will just have to wait for a donor SE.

 

[LCGuy]

I doubt its a Classic/Classic II board - first things first, the Classic/Classic II board won't fit in a SE case without modifications, you would also need to modify the connector going to the logic board, in addition the Classic/Classic II board lacks a brightness control, which the SE board has. If you still think you have a Classic/Classic II board, there's an easy way to find out - open it up and have a look...if its an SE board, the power supply will be metal box separate to the analog board, whereas the Classic/Classic II analog board has the power supply electronics built into the analog board.

I'm surprised that the voltages would be that different - I thought they'd all be about the same throughout all the compact Macs.

 

[Concorde1993]

Hello LC Guy:

Well, the SE I own has a brightness control knob, so the theory that I may have a Classic board seems to be virtually impossible.

By any chance, were there any Revision B analog boards for the SE series (not including the SE/30; I doubt the analog board I have could be from an SE/30)? The SE I have is somewhat unique, as it is labeled "SuperDrive", as opposed to "FDHD," and predates 1989 (the unit was built sometime in 1988, as the copyright date on the back states 1988). I would have to go online to decode the serial number to find out when exactly it was built, although I doubt it may solve this incompatibility issue.

I know for a fact that the 88 Plus was built in Singapore, and the 88 SE (with the screen-burn) was built in Fremont, USA. Would this be of any significance?

 

[Mac128]

The term SuperDrive came after the term FDHD. So what you have is a later model FDHD. The SE FDHD did not appear until late 1989, after the SE/30, and sold for a year, until it was replaced by the Classic. Yours is likely a 1990 model.

The Power Supply for the SE/30 & SE/FDHD/SuperDrive were identical. The copyright date of the power supply is irrelevant. All it indicates is that it was updated in 1988 (from the original 1987 design), and not updated again by the time it was installed in your SE.

 

[tomlee59]

The following morning, I received a phone call from the technician, who stated that the Plus display was incompatible (the voltage on the Plus was rated at 30, whereas the voltage on the SE was 400).

Your technician is deeply confused -- so much so that it brings into question his abilities. It's obvious that he does not have the slightest understanding of how a crt is driven.

There is no "voltage rating" for a crt, so I have no idea what the numbers 30 and 400 are supposed to mean. He is probably reading off of some data sheet filled with typos. His lack of fundamental knowledge prevents him from ignoring spurious information. A crt has several electrodes, whose voltages should be held within certain limits for safe/satisfactory operation. Rest assured, the Plus and SE have completely compatible crts (both mechanically and electrically). I, and others here, have verified this experimentally countless times, so we're not just making this up.

Just fyi, the Plus/SE crt uses a 12V filament ("heater"), and operates with about 10kV on the final (2nd) anode. For typical voltages on the other electrodes, see http://68kmla.org/files/classicmac2.pdf. Feel free to convey that document to your tech (if you trust him with further work).

 

[Concorde1993]

Thanks for the reply.

I read over the document you sent me (thanks again for that). The technician I dealt with was probably referring to the Plus' deflection yoke, which is not interchangeable with the SE's CRT. The voltage difference he was referring to does confuse me a bit (one would figure that the voltages would be identical, as the CRTs are identical) however, he has done service work on my 512ke (4 capacitors were replaced on the C circuit as a vertical line appeared on the CRT), and on the SE (the 3.6 volt battery was replaced, and the cooling fan was re-lubricated), and things seem to be working fine after several months since the servicing was completed.

My knowledge on discharging CRTs, and replacing capacitors is very limited (but I intend to learn how to complete these tasks in the near future), hence why I trust the expertise of my TV technician.

 

[tomlee59]

The yokes are fully compatible between the Plus and SE, mechanically, electrically, and pin-connection-wise.

But even if there were a yoke incompatibility, it would have no bearing on a crt replacement, for one could always replace only the crt, leaving each yoke with its original mac. When swapping crts between Classics and the SE, e.g., this is what you need to do because in that case, the yokes are indeed incompatible.

You should seriously consider doing the operation yourself. It requires no special skills -- just the temperament to work deliberately and carefully, and the ability to follow directions.

 

[Bunsen]

That or find a tech who knows what they're doing. Lubing a fan and replacing a few caps is nothing special.

 

[Concorde1993]

Thank you all for the replies.

Although I do not want to bash my TV technician as being an imbecile, or inexperienced (that was not my intention anyway), I am a hands-on person, and naturally I would appreciate any instructions, which are useful in completing such a task, especially from someone who has transferred CRTs on the compact Macs.

I have opened the case to my 88 Plus several times (I have the original Apple Torx screwdriver to unscrew the case & a case cracker) to take a look around, and to see if that urban legend with the designer's signatures is actually true (and it is). My main concern, of course, is discharging the CRT, since I do not have the proper tools, or knowledge to do so.

Since the forum members who have replied to this post state that the CRTs are indeed compatible, any terminology or resources to backup my case is greatly appreciated, as naturally I would like to discuss this with my TV technician, and complete this task without having to purchase a donor SE.

 

[Scott Baret]

As the author of the CRT FAQ, I concur--the CRT of the Plus (and earlier models) is completely interchangeable with the SE series (all models) and Revision A Classics. Other parts such as analog boards and video boards aren't, but the CRTs themselves can be swapped. (Revision B Classics are the only compacts to use a non-compatible part with the rest of the line, and that part is the actual connector that attaches the CRT to the analog board).

The SE (new-style) and Classic (both types) automatically discharge the CRT. Earlier models supposedly don't; if you want to build a discharge tool there are instructions all over the web. Some prefer to wait for the CRT to discharge on its own by leaving the Mac unplugged and turned off for a few weeks. Even if you do use a discharge tool, it's best to leave the Mac unplugged for a little while.

 

[Osgeld]

if you want to build a discharge tool there are instructions all over the web

and dont do it though the chassis ground, do it from the lugs on the front of the crt

your not really discharging anything, capacitors are most like a tank with a bladder in the middle, fill up one side the bladder expands which also builds up force on that side, if you connect the 2 sides together they will even back out, but "evening out" I guess was too hard for the old timers (like 1930's tv techs) to understand?

letting that force release though the ground plane on any part of the ciruit will most definitely fry something, usually something in the digital - logic areas where its weakest, yea the force of the capacitor (the largest one in the system the CRT tube) is removed, but in the most destructive way possible

its like disarming a 2 part chemical bomb by blowing it up, instead of clipping the green wire to keep it from mixing

 

[tomlee59]

My main concern, of course, is discharging the CRT, since I do not have the proper tools, or knowledge to do so.
Since the forum members who have replied to this post state that the CRTs are indeed compatible, any terminology or resources to backup my case is greatly appreciated, as naturally I would like to discuss this with my TV technician, and complete this task without having to purchase a donor SE.

Instructions for discharging the crt are in the document I linked to earlier. There's even a photo showing the proper discharge location, as Osgeld alluded to.

No special tool is needed. Don't even bother with a current-limiting resistor -- online advice about this is simply wrong (high-voltage resistors are special; use of ordinary resistors is like using none at all, so might as well keep things simple).

As far as terminology/resources/etc., with which to convince your tech, either he accepts what we say, or he doesn't. It all depends on whether he's sufficiently self-aware to understand his level of ignorance. I have swapped quite a few crts in compact macs, dating back to the late 1980s, and reverse-engineered the analog board (the result of which is the doc I pointed you to). If he's not willing to defer to those with that much greater experience, then just leave it be, and do the job yourself. It'll be less trouble than to convince your tech that all would be well.

 

[Bunsen]

whether he's sufficiently self-aware to understand his level of ignorance.

http://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect

Just sayin'

 

[Concorde1993]

Thanks again for the replies.

I will see about swapping the displays myself, and what turns out of it.

I doubt that anyone on this forum is from Southern Ontario (Canada), but if you know someone who lives somewhere within the Greater Toronto Area, and is willing to swap the displays, let me know as soon as possible. The SE will work with the screen-burn (it has for the past 4 + years), but I know that one day that CRT will not turn on.

Out of curiosity, when the CRT on a compact Mac fails (basically reaches the end of its life), and the capacitors/power supply are not the culprit, does it have any effects on any of the Mac's internal components (ie., analog/logic board)?

 

[Interceptor2]

If this was at my house it would be fun. First check is the CRT part number (Mfr) which are usually long affairs. The easy option is to get an exact replacement. Also check the scan coils, they might have a similar number. I've just looked on my Mac Plus and the numbers are there. Get the same parts and do a swap. As we all know the CRT comes with the scan coils glued on, keep it that way.

I would think all these little Mac CRTs are virtually the same execpt from those with the new diode split EHT transformer (Classic/II) - I would have to do a proper check. The key things are: glass bit - heater voltage, the final anode will be all about the same. The yolk: inductance of the vert/horiz coils, unless you're equipped with a bridge, go by part number.

Basically the horiz yolk inductance needs to have the correct tuning cap, the Plus is 33nF (I recall) maybe the Classic has a diff value. This arrangement is crucial (never change the tuning cap without knowing what might happen - boom).

So once I'd done those simple checks I'd do a CRT swap. Things that could happen (go wrong) fizzing, crack and small blazing pik - EHT too high, turn off! bad swap!

Heaters glow really BRIGHT (orange->yellow->flashbulb bright) - heater voltage wrong, modify. And so on, quite fun. All one hand in trouser pocket and on rubber mat (or wear rubber boots) stuff.

I've never had a CRT go boom on me, a few EHT transformers though. Be careful if it goes wrong there can be some mad voltages lurking which will bite and destroy.