Info-IBMPC@WSMR-SIMTEL20.ARMY.MIL ("Info-IBMPC Digest") (11/18/90)
Info-IBMPC Digest Sun, 18 Nov 90 Volume 90 : Issue 187
Today's Editor:
Gregory Hicks - Rota Spain <GHICKS@WSMR-Simtel20.Army.Mil>
Today's Topics:
Re: IBM Monitor Repair Notes: 8512, 8513, 3192
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Date: Fri, 9 Nov 90 19:25:16 -0500
From: rjbolger@vax1.tcd.ie
Subject: Re: IBM Monitor Repair Notes: 8512, 8513, 3192
A few months ago Frank Reid posted a few tips on the repair of IBM
screens including the 8512 and 8513 models from the PS2 range. They
appeared in Sci.electronics and I for one found them very useful
(especially since I.B.M. don't repair PS2 hardware out of warranty (in
Europe anyway)).
So without Frank's permission I'll re-post them here in the hope that
they may be of use to someone.
IBM MONITOR REPAIR NOTES: MODELS 8512, 8513, 3192
-------------------------------------------------
14 August 1990. rev: 22 Aug. 90
8512, 8513
----------
IBM's "PS/2" VGA color monitors, model 8512 and 8513, have been major
maintenance nightmares here and reportedly elsewhere. There are at
least two different models of each monitor, manufactured by Tatung of
Korea.
Schematic diagrams are apparently unavailable. The following is a
summary of many frustrating hours at the repair bench:
Opening the cases:
The top of the 8512 or 8513 case is fastened either by two internal
plastic clips (see below), or "tamperproof" Torx T-20 screws with
center pins. The Torx driver must have a long, slender shaft
(preferably magnetic) to reach the screw heads.
S/N 23-xxxxx: Plastic clips hold top front of case: Insert long, thin
screwdriver into rectangular holes and push clips downward. Use Apple
Macintosh case-separation tool to help remove back cover. This model
has the AC power connector soldered to the board: Look for cracked
solder joints first (see below).
NOTE: Cut the silicone glue at the CRT base and unplug the tube before
working on the main board! The glass neck is easily broken. A monitor
with broken CRT is not economically repairable. The voice of experience
speaks. :-)
Symptom: No power or intermittent power.
Some models have the AC power connector soldered directly to the main
circuit board. The wave-soldered connections are too thin for heavy
components or those subject to flexure: They crack, opening the
circuit. Resolder them, using lots of solder. Also use a magnifying
lens to inspect the solder joints of the flyback transformer and the
deflection-yoke connector. These often fail in the same manner as the
power connector. I always resolder all the abovementioned connections
on general principle.
Symptom: Horizontal line across screen, remainder black.
Failed component: Vertical amplifier (large IC attached to heat sink;
TDA-1670A manufactured by SGS, whose quality control is infamous).
People at IBM have told us that this chip is a weak point. Use heat-
sink compound when installing new IC. The replacement IC may last
indefinitely, or may fail in a few days. We have not tried Sylvania's
replacement, ECG 1862.
When the IC fails, a 2.2 ohm 1/4-watt resistor in series with the power
supply lead (diode and capacitor leading to a flyback pin) burns beyond
recognition. This resistor is used as a fuse. The value is not
critical (may be up to 20 ohms) but be sure the replacement is a
metal-film type resistor which burns quiescently, instead of a carbon
resistor which will start a fire. Leave the resistor leads long,
mounting the resistor one inch above the circuit board.
Before replacing IC, inspect for cracked solder connections on the male
deflection-yoke connector (mounted on the main circuit board).
Symptoms:
1) Immediate power supply shutdown.
2) Power supply shutdown/restart about once per second.
3) Squeal from power supply, wavy left and right edges of picture;
may become normal after warmup.
Bad component: C120 (10 uf 35v). This capacitor is common to all
four models of 8512/8513, and has the same identifying number on the
circuit board. It is located near front of the power supply area, in
the corner with the green LED pilot light, sometimes near a large green
resistor. Replace this capacitor on general principle anytime you open
an 8512 or 8513. This capacitor fails from heat; dissection of bad
capacitors reveals no moisture within. The replacement should have a
temperature rating of 105 deg. C. (typified by end plug made of epoxy
instead of rubber).
Symptom: Blown fuse
Bad component: De-gaussing thermistor (rectangular black box with 3
leads, near de-gauss coil connector).
We are thus far unable to find replacements. Remove the shorted device,
use a hand-held de-gaussing coil after the monitor has been returned to
its operating position.
(Rare): Blown fuse may result from shorted diodes which rectify 115
VAC power, or from shorted power-supply switching transistor. The
transistor base is transformer-coupled, so normally looks like a DC
short when you attempt to test the base-emitter junction in-circuit
with an ohmmeter.
Symptom: Bad power supply (in model whose power supply is a separate
unit in gold-colored metal cage), verifiable by swapping for known-
good power supply:
Replace two small electrolytic capacitors located under a rectangular
ceramic power resistor which stands about 1" above the circuit board.
8512 s/n 72-xxxxxxx (7 digits after 72-) This model has extensive metal
shielding inside. The power supply is a separate unit in gray metal
housing. Power cord permanently attached, cover has Torx screws:
Symptom: Squealing sound from power supply; supply operates normally
when 2-wire (red/white) power connector is removed from CRT board:
Failure: One or more shorted video driver transistors: 2SC3502,
2SA1370. (No ECG equivalents are listed.)
IBM agreed (offer now expired) to replace failed 8513 monitors having
serial numbers with prefix 72 and less than 064 (s/n 72-0640000 or
less). That series appears no less reliable than others. Replacements
have thusfar been trouble free.
Many of our 8512 and 8513 monitors (including picture tubes) have
failed from long service-- Since they have independent power switches,
and the screens are black when the computer is turned off, users tend
to leave them on forever.
Symptom: No picture, no high voltage; pilot lamp on or blinking:
Replace flyback transformer. We have had many flyback failures, and
have located a good source of replacements:
Component Resource Corp.
15316 East Valley Blvd.
City of Industry, Ca. 91746
1-800-366-1272
This company also has replacement flybacks for DEC VT-240 color
monitors (actually manufactured by Amdek).
Before replacing flyback: Look for broken solder connection at flyback
pins and deflection yoke connector.
The horizontal-output transistor appears robust; we have never replaced
one, even after flyback transformer failure.
Symptom: One color absent or displayed improperly.
The large circuit board attached to the CRT socket contains the cathode
drivers for each color. The large output transistors and their driver
transistors often fail. Apply a test pattern (e.g., white-on-black
text) and use an oscilloscope to compare the three color channels, to
locate the failed component(s).
Before we discovered the most common problems of 8512 and 8513 and
located a source of replacement flybacks, we had several repaired (with
good results) by:
Circuit Test, Inc.
12479 W. Hillsborough Ave.
Tampa, Florida 33635
IBM 3192 CRT Terminal
The IBM 3192 "administrative" terminal's monitor has insides
reminiscent of the 8512 and 8513 PS/2 VGA monitors (see above).
Case Removal:
The back cover of the monitor is held by two screws on the bottom and
two plastic spring-clips on the upper left and right sides (visible
with flashlight through rear ventilation slots). Use two L-shaped
tools (e.g., back-plates from IBM PC), inserted through upper side
ventilation-slots, to depress both clips simultaneously. Then lift the
cover off.
Symptom: No picture; repetitive clicking or beeping sound.
Bad part: High-voltage divider (the assembly between the flyback
transformer and the CRT anode), IBM part number 6405282 (about $20).
Replacement is easy: Unclip and unplug the tube and circuit-board
ends; pry the red plastic retaining ring out of the flyback, save it
for the new divider assembly.
Voltage-divider failure causes other damage in about 50% of 3192's: The
picture rolls vertically after the HV divider is replaced. The bad
component is IC303, which is a 7406 (TTL open-collector hex inverter).
Installing a 14-pin socket at IC303 may be advisable.
Most 3192's have integrated circuits with proprietary numbers. We were
fortunate to find a unit with mostly industry-standard numbers:
IC301 TDA2582
IC302 74LS221
IC303 7406
IC800 LM320T-12 (voltage regulator)
IC801 ?
Vertical amplifier: TDA2653A
Connect terminal to the appropriate communications system and adjust
the picture as needed, before replacing the back cover. The upper knob
on the flyback transformer is CRT focus, the lower knob is screen
voltage (a.k.a. "sub-brightness").
Symptom: No power, blown fuse.
The de-gaussing thermistor has probably failed (see 8512/8513 notes).
Before replacing fuse, use analog ohmmeter, or diode-test function on
DVM, to check the junctions of the two large power transistors in the
power supply section.
Frank Reid reid@ucs.indiana.edu
And remember, no-one ever got sacked for buying I.B.M. - just frustrated.
Richard Bolger //
Trinity College Dublin // rbolger@vax1.tcd.ie
Republic of Ireland //
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End of Info-IBMPC Digest V90 #187
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