TweetFollow Us on Twitter

Jan 89 Letters
Volume Number:5
Issue Number:1
Column Tag:Letters

Letters

By David E. Smith, Editor & Publisher, MacTutor

Overriding ROM Resources

Ronny Zulaikha

Sydney, Australia

When Apple upgraded to the 128K ROM, some of the extra space was filled with ROM resources that were previously only held in the system file. This saves time in that these resources aren’t loaded from the system file when needed, and saves space in that RAM isn’t taken up by them.

If one is designing a resource that is to replace one in the ROM, merely placing the new resource in the system file is not sufficient. As described in IM IV-20, one needs an ‘ROvr’ resource ID 0, which my system file (4.3) already had. This resource startup scans the system file for ‘ROv#’ resources of any ID, which indicates what resources to override. The first word of a ‘ROv#’ resource is the version number of ROM to override, and is $75 for the 128K ROM. For the SE and Mac II, it would be reasonable to assume that the version numbers listed in IM V-xvii would apply, $76 and $78 respectively. In fact, the routine in the ‘ROvr’ resource checks against the version word at location 8 higher than the start of the ROM. The high order byte is 0 for the 128K ROM, 1 for the Mac II and 2 for the SE, while the low order byte is the ROM version number. Putting this together, we get $276 for SE and $178 for the Mac II

Optimized String Comparisons

John S. Stokes III

San Diego, CA

My routine to compare two Pascal strings uses substantially less code than the “optimized” routine published in Donald Koscheka’s HyperChat column in November, 1988 issue of MacTutor. In my routine, the Pascal string length fields are compared as just another character in the comparison loop instead of separately.

;1

A0 -->  Pascal string 1
A1 -->  Pascal string 2
D0 <--   0 if false, 1 if true
D1 <--  work

CompareString  Moveq #0,D0; initialize flase return code
 Move.B (A0),D1  ; length of the first string
 Ext.W  D1; dbra uses word
@10Cmp.B(A0)+,(A1)+; match?
 Bne.S  @900; no
 Dbra D1,@10; yes, continue
 Moveq  #1,D0  ; set return code to true
@900  Rts ; return

NOTE: See Mar 89 Letters for bug fix and comments about this code.

Power Supply Board

David B. Lamkins

Canton, MA

Thanks to MacTutor, my Mac is alive and well at minimal expense following a sudden failure of the power supply board. Over a period of a couple weeks, under light use, my screen went from an occasional “blink” (accompanied by a snapping sound) to a thin vertical line. I recalled that there was a discussion of these symptoms in Mactutor, and found a detailed description of the problem and its cure in the June and July 1987 issues.

I’d like to shed some additional light on the subject, since I suspect that many owners of older Macs will face the same problem eventually. The Macintosh power supply board (which also provides the circuitry to operate the display) contains a wide range of parts, from integrated circuits to high-power components. It is tricky to solder the full range of these components on a wave solder machine --too little heat and the leads of the large components don’t get properly soldered, too much heat and the delicate components get fried.

I found a crack around J1 pin 4, just as indicated in the earlier articles, and signs of developing cracks around the other pins of J1. I removed the old solder with a solder bulb and carefully resoldered all four pins. What surprised me was that I found that NO solder had flowed between the pins and the(I’m assuming --too late to check) plated through holes in the PC board. Thus, the contact area was limited to a very thin film of solder bridging the connector pin to the foil on the PC board. It’s no wonder there was local heating leading to a joint failure!

I also found a bad solder joint on one of the leads of a coil in the same horizontal sweep circuit, and resoldered that as well. In this case, it looked like the original connection suffered from either improper cleaning of the coil lead, or too little flux and heat during soldering. A quick check of the solder joints on the remaining showed a potential problem on the end pins of the ten-pin power connector. Note that none of these problems were plainly visible to the naked eye --a magnifying glass was required

I found that the hardest part of the repair was locating the appropriate tools to open the Mac’s case. The readily available MacSnap Toolkit is not worth the expense --a long piece of allen wrench stock, which fits only some of the screws, is supplied in lieu of a Torx screwdriver. I returned this immediately for a refund. Local hardware, auto supply, appliance service, and specialty tool stores (I tried at least fifteen altogether) failed to produce a long-shafted Torx T-15 screwdriver. Least helpful was the service department of the local Apple dealer --”Sorry, they’re made exclusively for Apple. You can’t buy one unless you’re an authorized Apple repair center.” Finally, I turned to the MacTutor advertisers and called Computer Quick. For $20, these folks sold me a toolkit (separate screwdriver and case spreader) as good as any seen in an Apple service department.

My Mac started life three and a half years ago as a 512K. A year later, it was upgraded to a 512 enhanced, and stuffed with 4 megs of RAM and a piezo fan a year after the first upgrade. I have never had even a hint of a power supply problem during all this time. The time from onset of the first “glitch” to total failure was only a couple of weeks of light use --perhaps twenty hours of power-on time. From what I’ve seen, I strongly recommend that owners of earlier Macs take very seriously any signs of trouble with their display.

Whatever you do, don’t “fix” a jittery display by banging on the side of the case, as I’ve heard some people will do --this will only prolong the symptoms and probably will cause more extensive damage due to internal heating of bad solder joints. If you see the onset of this problem, you probably shouldn’t leave your Mac unattended while powered on. I suspect that the failure of the yoke connection for the horizontal sweep could unduly stress related components, leading to more serious failures than can be recovered with touch-up soldering.

Finally, if you do experience the “thin vertical line” death of your Macintosh, check the solder joints as mentioned here. If you don’t know how to solder, or have never worked on a television or video monitor circuit, enlist the help and advice of a friend who has. Failing that, you may want to consider a board exchange via some outfit like Computer Quick on the west coast, or Pre-owned Electronics in the Boston area. You’ll save money and time compared to the service provided by many Apple dealers.

Linear Equations

C. H. Friend

Watford, Herts, England

The article by Dave Kelly in the September MacTutor takes a long way around to do the following, which is the way it would appear in most math textbooks about solving linear systems of equations:

REM Solve equation system using inversion by MAT routines
REM mod CHF: 2/10/88 for TrueBasic 2.0 on Mac II
OPTION BASE 1
DIM A(3,3), V(3,3), B(3,1), X(3,1)
REM MacTutor Sep’88 example:
REM coefficient matrix [A]:
DATA 1, -4, 4, -1, 6, -3, 1, 0, -1 ! equation coefficients
REM right-hand side vector (b):
DATA 7, 0, 7! equation data
REM System is [A]x(X) = (b)
MAT READ A
MAT READ B
PRINT “Coefficients:”
MAT PRINT A
REM inverse of coeff. matrix, [A]^-1
MAT V=INV(A)
PRINT “Inverse:”
MAT PRINT V
PRINT “right-hand sides:”
MAT PRINT B
REM Solution vector, (X) = [A]^-1 x (b)
MAT X = V * B
PRINT “Solution:”
MAT PRINT X
END

Results obtained are shown below:

Ok. run
Coefficients:
1-44
-1 6  -3
10 -1

Inverse:
.428571 .285714  .857143
.285714 .357143  7.14286e-2
.428571 .285714  -.142857

right-hand sides:
7
0
7

Solution:
9
2.5
2

Ok. Bye

You also refer to Hewlett-Packard Basic, on HP9000 Series machines. The Matrix ROM on HP’s smaller Series 80 machines has had an extensive set of matrix commands and functions for some time. Series 200 HP-Basic has only just acquired some of these, such as the sub-matrix copy commands. Other useful HP-Basic functions are the row and column sums. These make powerful programs very short, e.g. the following example from “Probability and Statistics for Engineers and Scientists” by Walpole and Myers (MacMillan)

REM Multiple Linear Regression (W&M), HP86
REM mod 25/6/88 for TrueBasic on Mac II
OPTION BASE 1
DIM D(5,15), E(15,5), F(1,5), V(15,4), X(15,5), T(5,15)
DIM A(5,5), C(5,5), Y(15,1), Z(1,15), G(1,15), H(5,1)
DIM B(5,1), P(5,1), Y2(15)
DATA 4, 13
DATA 25.5, 31.2, 25.9, 38.4, 18.4, 26.7, 26.4,
DATA 25.9, 32, 25.2, 39.7, 35.7, 26.5
DATA 1.74, 6.32, 6.22, 10.52, 1.19, 1.22, 4.1
DATA 6.32, 4.08, 4.15, 10.15, 1.72, 1.7
DATA 5.3, 5.42, 8.41, 4.63, 11.6, 5.85, 6.62, 8.72
DATA 4.42, 7.6, 4.83, 3.12, 5.3
DATA 10.8, 9.4, 7.2, 8.5, 9.4, 9.9, 8, 9.1
DATA 8.7, 9.2, 9.4, 7.6, 8.2
REM
PRINT “Multiple Linear Regression:”
READ K,N
MAT REDIM D(K,N), E(N,K), F(1,K) V(N,K-1)
MAT REDIM X(N,K), T(K,N) A(K,K), Y(N,1)
MAT REDIM Z(1,N), G(1,K), H(K,1), P(K,1)
MAT READ D
REM
MAT E = Trn(D)
PRINT “Data:”
MAT PRINT USING “#####.##”: E
REM MAT F=CSUM (E) ! HP-BASIC
FOR J = 1 TO K ! TRUEBASIC
 LET F(1,J) = 0.0
 FOR I = 1 TO N
 LET F(1,J) = F(1,J) + E(I,J)
 NEXT I
NEXT J
PRINT “Sums:”
MAT PRINT USING “#####.##”: F
MAT X=Con
REM MAT V=E(,2:K) ! HP-BASIC
FOR I = 1 TO N ! TRUE BASIC
 FOR J = 1 TO K-1
 LET V(I,J) = E(I,J+1)
 NEXT J
NEXT I
REM MAT X(,2:K)=V! HP-BASIC
FOR I = 1 TO N ! TRUE BASIC
 FOR J = 1  TO  K-1
LET X(I,J+1) = V(I,J)
 NEXT J
NEXT I
REM PRINT “Ind.  variables:”
MAT T = Trn(X)
MAT A = T * X
PRINT “Equations:”
MAT PRINT USING “#####.###”: A
REM MAT Y=E(,1)
FOR I = 1 TO N
 LET Y(I,1)   = E(I,1)
NEXT I
MAT Z = Trn(Y)
MAT G = Z  *  X
MAT PRINT USING “#####.###”: G
MAT H = Trn(G)
REM MAT B=SYS (A,H)! HP-BASIC, solves linear system
MAT C = Inv(A)   ! TRUE BASIC
MAT B = C *  H
PRINT “Coefficients:”
MAT PRINT  USING “----,######”:  B “
PRINT “residuals:”
REM MAT Y2=Y.Y ! HP-BASIC allows dot product of vectors
FOR I = 1 TO N
 LET Y2(I)  = Y(I,1)
NEXT I
REM SY2=SUM (Y2) ! HP-BASIC  matrix function
LET SY2 = O.O
FOR I = 1 TO N
 LET SY2 = SY2 + Y2(I)
NEXT I
LET SY2N = G(1,1)^2/N
LET SST = SY2 - SY2N
MAT P = Trn(G)
REM MAT P=B.P
FOR J = 1 TO K
 LET P(J,1) = B(J,1)*P(J,1)
NEXT J
REM SBG=SUM (P)
LET SBG = 0.0
FOR J = 1 TO K
 LET SBG = SBG + P(J,1)
NEXT J
LET SSA = SBG - SY2N
LET NDF = N - K
LET ES2 = (SST - SSA)/NDF
PRINT USING “SST = ####.###”:  SST;
PRINT USING “, SSR = ####.###”: SSR;
PRINT USING “;  s^2 = ##,#####”: ES2
END

Results are:

Ok. run
Multiple Linear Regression:
Data:
 25.50  1.745.30 10.00
 31.20  6.325.42 9.40
 25.90  6.228.41 7.20
 38.40  10.52  4.638.50
 18.40  1.1911.609.40
 26.70  1.225.85 9.90
 26.40  4.106.62 8.00
 25.90  6.328.72 9.10
 32.00  4.084.42 8.70
 25.20  4.157.60 9.20
 39.70  10.15  4.839.40
 35.70  1.723.12 7.60
 26.50  1.705.30 8.20

Sums:
 377.50 59.43  81.82 115.40

Equations:
 13.000 59.430 81.820115.400
 59.430 394.726  360.662  522.078
 81.820 360.662  576.726  728.310
 115.400522.078  728.310  1035.960

 377.5001877.567 2246.661 3337.780

Coefficients:
 39.157350
 1.016100
 -1.861649
 -.343260

residuals:
SST = 438.131, SSR = 399.454; s^2 = 4.29738
Ok. Bye

Matrix statements were in the original DEC PDP Basic, developed by Kemeny and Kurtz. They were omitted from early microcomputer Basics, presumably for memory reasons. Another less useful feature of DEC Basic is this “####” print image stuff, HP-Basic uses the much neater “nD.mD” style (numbers of digits before and after the decimal point, plus other options for mantissa and exponent style, etc. [Thank you for an excellent treatment of an interesting subject. I am very interested in covering more such areas in scientific and engineering computing. After all, computers were origonally designed to solve problems, were they not? --Ed]

VIREX by HJC Software

Kirk Chase

Anaheim, CA

Last week I got a call at MacTutor from a Mr. Robert Capon about viruses. Actually, I’ve been getting a number of calls in the last few weeks about viruses. I thought that the virus war was over a few months ago, but just when you thought it was safe to power up your Mac Anyway, this call was about Virex, an anti-virus application due to hit the market by the time this issue hits the doorsteps.

Virex supposedly combats all three current computer viruses out there, namely the Scores Virus, the nVIR family, and the Peace virus, with more updates as more viruses are put out by #@*!! computer vandals. Virex reports to have the ability to not only detect but remove and repair damaged files.

Developed by known computer virus authority, Robert Woodhead, this little gem of software might be just what the doctor ordered for the sysop who phoned me a couple weeks ago whose network over the college campus seemed constantly at risk to these self-replicating monsters. I don’t know if it will be a complete help (probably not --sigh), but at a price of under a hundred dollars, software houses can certainly afford a little more protection.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

MacUpdate Desktop 6.0.8 - Search and ins...
MacUpdate Desktop 6 brings seamless 1-click installs and version updates to your Mac. With a free MacUpdate account and MacUpdate Desktop 6, Mac users can now install almost any Mac app on macupdate.... Read more
BitTorrent Sync 2.1.1 - Sync files secur...
BitTorrent Sync allows you to sync unlimited files between your own devices, or share a folder with friends and family to automatically sync anything. File transfers are encrypted. Your information... Read more
Quicksilver 1.3.0 - Application launcher...
Quicksilver is a light, fast and free Mac application that gives you the power to control your Mac with keystrokes alone. Quicksilver allows you to find what you need quickly and easily, then act... Read more
iWatermark Pro 1.72 - Easily add waterma...
iWatermark Pro is the essential watermarking app for professional, business, and personal use. iWatermark, is the number 1 and only watermarking tool available for all 4 platforms iPhone/iPad, Mac,... Read more
RapidWeaver 6.3 - Create template-based...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
Adobe Photoshop CC 2015 16.0.1 - Profess...
Photoshop CC 2015 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Photoshop customer). Photoshop CS6 is still available for purchase (... Read more
Together 3.4.6 - Store and organize all...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Smart storage. With simple drag-and-drop functionality,... Read more
Monosnap 3.1.0 - Versatile screenshot ut...
Monosnap lets you capture screenshots, share files, and record video and .gifs! Capture: Capture full screen, just part of the screen, or a selected window Make your crop area pixel perfect with... Read more
Cocktail 8.5.1 - General maintenance and...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
Vienna 3.0.6 :5eaf312: - RSS and Atom ne...
Vienna is a freeware and Open-Source RSS/Atom newsreader with article storage and management via a SQLite database, written in Objective-C and Cocoa, for the OS X operating system. It provides... Read more

Five Nights at Freddy's 4 has Been...
In keeping with tradition, Five Nights at Freddy's 4 has made its way to the App Store with zero warning fanfare. Honestly I'd be disappointed it if happened any other way at this point. [Read more] | Read more »
Doom & Destiny Advanced (Games)
Doom & Destiny Advanced 2.3.4.0 Device: iOS Universal Category: Games Price: $.99, Version: 2.3.4.0 (iTunes) Description: ---SUPER GIGA LAUNCH DISCOUNT! Get it now for cheap or pay more later!---An additional 143 MB download is... | Read more »
Five Nights at Freddys 4 (Games)
Five Nights at Freddys 4 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: This time, the terror has followed you home. | Read more »
This Week at 148Apps: July 27-31, 2015
Winding Down July With 148Apps How do you know what apps are worth your time and money? Just look to the review team at 148Apps. We sort through the chaos and find the apps you're looking for. The ones we love become Editor’s Choice, standing out... | Read more »
You'll Want to Keep an Eye Out for...
If you're the kind of person who had fun hunting down and completing all the codex puzzles in Assassin's Creed 2, then are you ever in for a treat. The Guides looks like it's going to be a very robust collection of similarily odd, seemingly... | Read more »
Vivid Games has Announced Real Boxing 2...
The original Real Boxing was a pretty impressive bit of fisticuffs, but if the trailer Vivid Games is showing off for GamesCom is any indication Real Boxing 2 is going to be even better. [Read more] | Read more »
PAC-MAN Championship Edition DX - Tips,...
[Read more] | Read more »
Card King: Dragon Wars - Tips, Tricks an...
[Read more] | Read more »
Pac-Man Championship Edition DX has brou...
Bandai Namco has released Pac-Man Championship Edition DX on iOS and Android, which features the classic arcade gameplay that we've all grown to love. Pac-Man Championship Edition DX can be enjoyed in much shorter bursts than the arcade versions... | Read more »
Cosmonautica (Games)
Cosmonautica 1.1 Device: iOS Universal Category: Games Price: $6.99, Version: 1.1 (iTunes) Description: Cast off! Are you ready for some hilarious adventures in outer space? | Read more »

Price Scanner via MacPrices.net

MacBook 12 Retina Pundit’s New Favorite Mac
If you’re eyeing the purchase of a new 12-inch Retina MacBook, but wondering if you can live with a single USB-C port, 2011-level CPU performance, and the unorthodox keyboard, you should find... Read more
PDF Element Tool Kit For PDF For Windows 10,...
South Surrey, British Columbia based software developer Wondershare has posted an interesting infographic tracking the development of Microsoft’s flagship Windows operating system over the years,... Read more
27-inch 3.5GHz 5K iMac on sale for $81 off MS...
Adorama has the 27″ 3.5GHz 5K iMac on sale for $2218, $81 off MSRP, including a free copy of Apple’s 3-Year AppleCare Protection Plan. Shipping is free, and Adorama charges sales tax in NY & NJ... Read more
Back-to-School with Tablet and Smartphone Acc...
Belkin helps you prepare for the coming school year with a wide variety of the latest mobile and tablet accessories to outfit both grade school and college students. The line-up includes charging... Read more
11-inch MacBook Airs on sale for $100 off MSR...
Best Buy has 11-inch MacBook Airs on sale for $100 off MSRP. Choose free shipping or free local store pickup (if available). Sale prices for online orders only, in-store prices may vary: - 11″ 1.6GHz... Read more
iPad Air 2 on sale for up to $100 off MSRP
Best Buy has iPad Air 2s on sale for up to $100 off MSRP on their online store for a limited time. Choose free shipping or free local store pickup (if available). Sale prices available for online... Read more
Sale! 13-inch MacBook Pros on sale for $100 o...
B&H Photo has 13″ MacBook Pros on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.5GHz/500GB MacBook Pro: $999.99 save $100 - 13″ 2.7GHz/128GB Retina... Read more
Sale! Save $100 on 13-inch MacBook Airs this...
B&H Photo has the 13″ 1.6GHz/128GB MacBook Air on sale for $899.99 including free shipping plus NY tax only. Their price is $100 off MSRP, and it’s the lowest price available for this model.... Read more
Worldwide Tablet Market Decline Continues, Ap...
The worldwide tablet market declined -7.0% year-over-year in the second quarter of 2015 (2Q15) with shipments totaling 44.7 million units according to preliminary data from the International Data... Read more
TP-LINK TL-PA8030P KIT Powerline Featuring Ho...
Consumer and business networking products provider TP-LINK is now shipping its TL-PA8030P KIT AV1200 3-Port Gigabit Passthrough Powerline Starter Kit that expands your home’s network over its... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Infrastructure Engineer - *Apple* /Mac - Hil...
Infrastructure Engineer - Apple /Mac Job Code: 1608 # of openings: 1 Description Our fortune 500 client is looking to hire an experienced Infrastructure Engineer to join Read more
Executive Administrative Assistant, *Apple*...
…supporting presentation development for senior leadership. * User experience with Apple hardware and software is preferred. Additional Requirements The following list Read more
*Apple* Bus Company is now hirin - Apple Bus...
Apple Bus Company is now hiring school bus drivers in the Pettis County area. Class B CDL preferred. Free training provided. No nights or weekends required. Flexible Read more
*Apple* Certified Mac Technician - Updated 6...
…and friendly, hands-on technical support to customers troubleshooting and repairing Apple /Mac products with courtesy, speed and skill. Use your problem-solving skills Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.