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

BBEdit 11.0.3 - Powerful text and HTML e...
BBEdit is the leading professional HTML and text editor for the Mac. Specifically crafted in response to the needs of Web authors and software developers, this award-winning product provides a... Read more
Microsoft Office Preview 15.8 - Popular...
Welcome to the new and modern Microsoft Office for Mac. You will receive regular updates automatically until the official release in the second half of 2015. With the redesigned Ribbon and your... Read more
Yosemite Cache Cleaner 9.0.5 - Clear cac...
Yosemite Cache Cleaner is an award-winning general purpose tool for OS X. YCC makes system maintenance simple with an easy point-and-click interface to many OS X functions. Novice and expert users... Read more
ExpanDrive 4.3.2 - Access cloud storage...
ExpanDrive builds cloud storage in every application, acts just like a USB drive plugged into your Mac. With ExpanDrive, you can securely access any remote file server directly from the Finder or... Read more
RapidWeaver 6.0.8 - Create template-base...
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
Artlantis Studio 5.1.2.7 - 3D rendering...
Artlantis Studio is a unique and ideal tool for performing very high resolution rendering easily and in real time. The new FastRadiosity engine now lets you compute images in radiosity-even in... Read more
MacUpdate Desktop 6.0.5 - 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 2.0.82 - Sync files secu...
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
Google Drive 1.20 - File backup and shar...
Google Drive is a place where you can create, share, collaborate, and keep all of your stuff. Whether you're working with a friend on a joint research project, planning a wedding with your fiancé, or... Read more
Simon 4.0.3 - Monitor changes and crashe...
Simon monitors websites and alerts you of crashes and changes. Select pages to monitor, choose your alert options, and customize your settings. Simon does the rest. Keep a watchful eye on your... Read more

New Publisher Allstar Games Heads West w...
Allstar Games has announced its first mobile title designed for western audiences, Allstar Heroes. The game will be a massive online battle arena (MOBA) that offers dozens of heroes for you to collect and pit against your opponents. As each hero has... | Read more »
RAD Boarding Review
RAD Boarding Review By Jennifer Allen on March 5th, 2015 Our Rating: :: NEARLY RADUniversal App - Designed for iPhone and iPad RAD Boarding isn’t quite one of the greats, but it has potential.   | Read more »
Presenting the International Mobile Gami...
11th Annual International Mobile Gaming Awards ceremony, hosted by actress Allison Haislip, gathered mobile game developers and publishers from around the world. They chose 13 winners out of the 93 nominations. British studio USTWO won the the Grand... | Read more »
AG Drive Review
AG Drive Review By Tre Lawrence on March 5th, 2015 Our Rating: :: FUTURISTIC STREET RACING.Universal App - Designed for iPhone and iPad Futuristic racing… interstellar style.   | Read more »
GDC 2015 – Nightmare Guardians is an Int...
GDC 2015 – Nightmare Guardians is an Interesting Hybrid of MOBA and Lane Defense Posted by Rob Rich on March 5th, 2015 [ permalink ] I have to say that lane defense (i.e. | Read more »
Overkill 3 Review
Overkill 3 Review By Tre Lawrence on March 5th, 2015 Our Rating: :: WHO'S NEXT?Universal App - Designed for iPhone and iPad Cover system gameplay in the third-person.   Developer: Craneballs Price: Free Version Reviewed: 1.1.6... | Read more »
Warner Bros. Interactive Entertainment A...
Warner Bros. has some exciting games coming down the pipe! | Read more »
GDC 2015 – Star Trek Timelines will Prob...
GDC 2015 – Star Trek Timelines will Probably Make Your Inner Trekkie Squeal With Glee Posted by Rob Rich on March 4th, 2015 [ permalink ] Any popular fictional universe has its fair share of fan fiction – where belo | Read more »
Protect Yourself from an Onslaught of Ca...
Surprise Attack Games has announced a Cat-astrophic new physics puzzler called Fort Meow! In the game, a young girl named Nia finds her grandfather’s journal which triggers an all mighty feline attack! Why do the cats want the journal? Who knows,... | Read more »
GDC 2015 – Jelly Reef will be Game Oven’...
GDC 2015 – Jelly Reef will be Game Oven’s Last Hurrah, and it Seems like a Good Note to Go Out on Posted by Rob Rich on March 4th, 2015 [ permalink ] It’s sad knowing that Game Oven ( | Read more »

Price Scanner via MacPrices.net

Roundup of MacBook Air sale prices, models up...
B&H Photo has MacBook Airs on sale for up to $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 128GB MacBook Air: $799 100 off MSRP - 11″ 256GB MacBook Air: $999 $100... Read more
New Firstrade Mobile App Enables On-The-Go Tr...
Firstrade Securities Inc. has announced its new mobile app, which gives investors immediate access to the company’s trading platform on all mobile devices. The app was developed in-house and was... Read more
Sonnet Introduces USB 3.0 + eSATA Thunderbolt...
Sonnet has announced the launch of its new USB 3.0 + eSATA Thunderbolt Adapter for easy connectivity to USB 3.0 devices and eSATA storage, and USB 3.0 + Gigabit Ethernet Thunderbolt Adapter for easy... Read more
Apple restocks refurbished 27-inch 5K iMacs f...
The Apple Store has restocked Apple Certified Refurbished 27″ 3.5GHz 5K iMacs for $2119 including free shipping. Their price is $380 off the cost of new models, and it’s the lowest price available... Read more
Free Clean Reader Mobile App Hides Swear Word...
The new Clean Reader app, now available in the Apple App Store and Google Play, delivers the opportunity of reading any book without being exposed to profanity. By selecting how clean they want their... Read more
Kinsa Launches “Groups” App to Monitor Illnes...
Kinsa, makers of the first FDA approved app-enabled smartphone thermometer thst won the 2013 Cleveland Clinic Medical Innovation Grand Prize and recently appeared in Apple’s “Parenthood” TV... Read more
iPad: A More Positive Outlook – The ‘Book Mys...
It’s good to hear someone saying positive things about the iPad. I’ve been trying to bend my mind around how Apple’s tablet could have gone from zero to bestselling personal computing device on the... Read more
Mac Pros on sale for up to $279 off MSRP
Amazon has Mac Pros in stock and on sale for up to $279 off MSRP. Shipping is free: - 4-Core Mac Pro: $2725.87, $273 off MSRP (9%) - 6-Core Mac Pro: $3719.99, $279 off MSRP (7%) Read more
Sale! 13-inch Retina MacBook Pros for up to $...
B&H Photo has 13″ Retina MacBook Pros on sale for up to $205 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.6GHz/128GB Retina MacBook Pro: $1219.99 save $80 - 13″ 2.... Read more
Another Tranche Of IBM MobileFirst For iOS Ap...
IBM has announced the next expansion phase for  its IBM MobileFirst for iOS portfolio, with a troika of new apps to address key priorities for the Banking and Financial Services, Airline and Retail... 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
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
Position Opening at *Apple* - Apple (United...
…Summary** As a Specialist, you help create the energy and excitement around Apple products, providing the right solutions and getting products into customers' hands. You Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** The Apple Store is a retail environment like no other - uniquely focused on delivering amazing customer experiences. As an Expert, you introduce people Read more
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.