Author: Frank Reid
E-Mail: reid@indiana.edu
Release: Aug 14, 1990
Revisions: Aug/Nov/Dec 1990, Jan/Apr/May/Sep/Oct 1991,
Feb/Mar/Sep 1992, Aug 1993, Jan/Mar/Aug/Oct 1994, Feb 1995
(Version is Internal)
IBM's "PS/2" VGA color monitors, models 8512 and 8513, have had frequent maintenance problems. There are at least two different models of each monitor. They are manufactured in Korea, probably by Samsung or Tatung.
Schematic diagrams are apparently unavailable. The following is a summary of many frustrating hours at the repair bench:
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. The internal catches can be released by inserting a pair of special tools made of sheet-metal, shaped approximately like:
_____ /|
______________________________| | |
\_____________________________ | |
|_____|/
The angle at the end is more acute (25 degrees) than shown in this ASCII diagram.
Alternatively, insert long, thin screwdriver into rectangular holes and push clips downward. An Apple Macintosh case-separation tool is sometimes useful to help remove back the cover. It is best to release both clips simultaneously.
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 (including those whose serial numbers begin with 23) 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, the deflection-yoke connector and (rarely) the CRT socket. These often fail in the same manner as the power connector. I always resolder all the above-mentioned connections on general principle.
Symptom: High voltage present but screen dark
Inspect solder joints on CRT socket, especially if serial number begins with 23-. (See above.)
Symptom: Horizontal line across screen, remainder dark
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. Sylvania's ECG 1862 is a replacement for TDA1670A.
When the IC fails, a 2.2 ohm 1/4-watt resistor in series with its 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 resistor is a metal-film type which burns quiescently, instead of a carbon resistor which will start a fire. Leave the resistor leads long, mounting the resistor one inch [2cm] mabove the circuit board.
Before replacing IC, inspect for cracked solder connections on the male deflection-yoke connector (mounted on the main circuit board).
In old monitors, especially 8513 with serial numbers beginning with 72- , replace vertical deflection-yoke coupling capacitor C313 (3.3 uF 160v), especially if it shows signs of overheating (shrink tube retracted from top of metal can).
Also check C309 (2200uf 16v). If C309 is bad, the new amplifier may fail immediately or in a few days.
Symptoms: Power Supply Problem:
Bad component: C120 (10 uf 35v). This capacitor is common to most models of 8512/8513, and has the same identifying number on their circuit boards. It is located near the 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). Heat-induced capacitor failure is a common problem in switching power-supplies. If high- temp. capacitors are unavailable, leave the leads long so that the new capacitor can be placed further from the abovementioned resistor which gets hot enough to discolor the circuit board and adjacent plastic standoff.
If capacitor is good, check diode CR105. This diode sometimes has thermal problems resulting in intermittent or permanent short, causing symptoms as above. Replace with a fast-recovery diode such as 1N4937; leave leads long for cooling. (We use 1N4937 as a generic replacement for high-frequency rectifiers in monitors, both in switching power supplies and flyback-derived voltage sources. Common rectifier diodes such as 1N4004 will overheat when used at the frequencies of switching power supplies or of flyback transformers.
Also check CR212, near the flyback transformer. It often shorts. Rating is 3A, 600V.
Symptom: Blown fuse
Bad component: De-gaussing thermistor (rectangular black box with 3 leads, near de-gauss coil connector).
If new thermistor is unavailable: Remove the shorted device, use a handheld de-gaussing coil after the monitor has been returned to its operating position.
Replacement thermistors are not available from IBM. A suitable replacement for the thermistor in IBM 8512, 8513 and 3192 is the one used in NEC 1401 monitors. It is NEC part number 38112026, "positive thermistor degaussing control," $2.95 from:
NEC Home Electronics
1255 Michael Dr.
Wood Dale IL 60191-1094.
The NEC device is slightly larger and apparently more robust than the original. On some types the middle leg must be bent to fit the hole in the printed-circuit board.
(Rare): Blown fuse may result from shorted diodes which rectify 115 VAC power, or from shorted FET power-supply switching transistor.
Bad power supply (in model where 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.
Symptom: 8513 s/n 23-xxxxx: R203 burned
Replace resistor (120 ohms, 1/4 watt), resolder C202. C202's solder joints often break from vibration, or from being bumped during chassis disassembly/reassembly.
Symptom: 8513 23-xxxxx, single bottom-screw, metal subchassis, crt-board shield with top overhang: Red color very dim or absent:
Resolder broken connections on the "red cut" control (RV801 on the CRT board). The manufacturer produced a large number of this model with that device improperly installed. Re-balance colors as necessary.
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.)
Symptom: No power, or power supply making squealing sound. Exploded capacitors on CRT board or inside power supply:
Replace exploded capacitors (10 uf 100v) as required. Replace C18, C21 and C22 in the power supply. Use high-temperature types. Failure of these capacitors may cause the power supply's regulation to fail, causing power filter and video decoupling capacitors to explode. The power supply to the CRT board should deliver aprox. 70 volts.
Symptom: Vertical foldover, possibly decreasing with
warmup: replace C408 and C425 (near extruded heatsink).
Symptom: One color absent or displayed improperly, or "2401"
error.
Problem: Bad video cable. Wires often break inside the connector. There are several variations of the inner end of the cable. The one most prone to failure is used on 8512 s/n 72-xxxxxxx. Its IBM part number is 61X8888. It is also available from other sources.
New connectors are available from electronics parts distributors, but installing them is very difficult because the inner conductors of the coaxial cables are small and brittle. We have spliced a few cables recovered from junked monitors but that is a laborious process.
IBM agreed to replace some 8512 and 8513 monitors under certain conditions: See IBM documents 8512 ECA026 and 8513 ECA017. The replacement offer has long EXPIRED.
8512's: Serial number with "72" prefix, s/n between 72-0120000 AND 72-0405000: Display is out of focus and/or excessively bright.
8513's: Serial number with "72" prefix, s/n below 72-0640000: Display out of focus.
Those series appear no less reliable than others. Some replacement units were new, others are used/reworked and have new serial numbers attached. These appear to have new flyback transformers. Some have subsequently failed for other reasons.
Symptom: Out of focus (8513 s/n 72-...)
If the focus control on the flyback is turned to the end of its travel and the display is still out of focus, replace the flyback. Replacement type is TFB-185A. The replacement may appear to have two controls instead of one; the control labeled SCREEN is a dummy (see below).
Many of our 8512 and 8513 monitors have failed from long service: Since they have integral power switches, and the screens are black when the computer is turned off, users tend to leave them on forever. Life will be significantly extended by turning them off overnight and on weekends.
CRT focus degrades with age. If the picture will not focus satisfactorily and the focus control is not at an extreme (see above), repair is not economical unless you have a good tube salvaged from a scrapped unit. Transplant the CRT and deflection yoke together; if the yoke is disturbed, reconvergence of colors is extremely difficult.
Symptom: Left and right edges of picture are curved inward (pincushion distortion); internal adjustments (E/W and Width) inoperative. Occurs after a few years' service.
Replace capacitor C225 (22uF 50v 105 deg.C).
Symptom: Fluctuating brightness due to erratic screen voltage in 8513 with serial number beginning 72-xxxx:
R477 (3.3M 1/4 watt) fails from high-voltage breakdown. Replace with same value, 1/2 watt, or two 1.6M 1/4w in series. Resistor is located between flyback transformer and aluminum heatsink of horizontal output transistor. This model 8513 has only one control (focus) on its flyback; the screen-voltage control is on the board attached to the CRT socket.
I replace this resistor on general principle in aging monitors, and readjust the screen voltage (variable resistor on CRT-socket circuit board). These monitors usually also need their color balance readjusted (controls labled R.BKG, G.BKG, B.BKG at rear of main board).
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
Connector pinout of IBM color VGA connector (model 8513):
1 Red video 9 Reserved 2 Green video 10 Ground 3 Blue video 11 Monitor sense (ground) 4 Reserved (absent) 12 Monitor sense (open) 5 Self test 13 Horizontal synch 6 Red video return (coax shield) 14 Vertical synch 7 Green video return (coax shield) 15 Reserved (absent) 8 Blue video return (coax shield)
The "self test" line causes a white raster on the screen when the cable is disconnected. The video signals are terminated at 75 ohms.
Model 8514 appears far more reliable than 8512 and 8513. Relatively few of them are in use at this location, and they have needed little repair.
Symptom: Squealing noise, vertically-unstable picture.
Replace the small electrolytic capacitors in the power supply. Use high-temperature types.
EGA (5154) and PGA (5175) monitors are nearly identical except for the video electronics contained in a metal box on the left side (when facing the screen). Schematics ARE available from IBM, in _Technical Reference, Options and Adapters, Volume 3_ of the "Personal Computer Hardware Reference Library." Introduced in the mid 1980's, many 5154 and 5175 monitors are nearing the end of their service lifetimes, i.e., tubes have dim picture and poor focus, and numerous capacitors' values have decreased. In severe cases, we advise users to scrap the monitors and convert to VGA.
The most common failure is in the power supply: Symptoms include chirping noise, repetitive startup/shutdown (blinking LED pilot lamp) or jagged edges on left and right of picture.
Replace three small electrolytic capacitors in the power supply: C11 (47uF 40v), C13 (10uF 35v) and C14 (1uF 35v). These capacitors fail from heat after long service.
The power-supply unit is removable. You must drill-out three pop- rivets to open the metal box; replace them with sheet-metal screws.
Symptom: Vertical foldover in EGA mode, or incorrect vertical centering.
Replace C311 (100 uf 40v) near vertical amplifier (IC300).
My employer, an enormous state university, has found it very economical to discontinue maintenance contracts on about eight hundred IBM 3192 terminals and repair them in-house. 3192 repairs are generally trivial, however, the assumed importance of the administrative functions for which they are used makes it extremely expedient to keep an adequate supply of spares available for instant replacement.
The 3192's color monitor has insides somewhat reminiscent of the 8512 and 8513 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 ventilation slots on the sides, to depress both clips simultaneously. Then lift the cover off.
Symptom: No power, blown fuse.
The de-gaussing thermistor has probably shorted. This is the most common failure we have encoutnered in 3192's. The thermistor is identical to those used in 8512 and 8513; see above. 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. Alternatively, measure resistance across the line-voltage filter capacitor (C107) with power OFF and capacitor discharged. The resistance should be greater than 500 ohms.
An intermittent "flutter" of the display can indicate incipient failure of the de-gaussing thermistor; it is supposed to conduct current through the de-gaussing coil for a few seconds during initial power-on. Prior to failure, it may begin to conduct during normal operation after warmup.
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 ends going to CRT and circuit-board. Pry the red plastic retaining ring out of the flyback transformer; save it for the new divider assembly.
We have had difficulty obtaining voltage dividers from IBM; an equivalent is available from Component Resource Corp (see address above), same part number. Its red high-voltage wire is larger in diameter than the original component: Use a 11/64" drill to enlarge the hole in the red ferrule on the flyback; use a flat file to reduce the bumps on the sides, and use a rat-tail file to make the split part of the plastic thinner.
Voltage-divider failure causes additional damage in about 50% of 3192's:
Symptom: Vertically-rolling picture (no vertical synch) but video is present over entire face of tube.
This symptom often appears 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.
Horizontal-synch problems may also result from failed IC303 (7406).
A severely-shorted voltage divider may pull power-supply voltages to low levels, resulting in the unit appearing dead (no pilot-light) although the fuse is intact. Disconnect the red HV wire from the flyback transformer, then apply power. If pilot light illuminates, replace voltage-divider.
A 3192 left on for a long time with shorted high-voltage divider will destroy multiple components in succession without blowing the fuse. All these parts may be bad:
Switching transistor Q201 (2SD1441 or 2SD1739 <b>*</b>)
Driver transistor Q101 (2SD836)
Look for burned transistors or other signs of high heat.
Flyback transformer (about 25% of cases)
One or both 0.82 ohm 5w resistors
7406 (IC 303)
Vertical amplifier TDA2653.
[*] Newer models of 3192 are recognizable by a lighter shade of green circuit board with a smaller parts count and natural-aluminum heat sinks (instead of black anodized). The power-supply switching transistor is 2SD1739 (ECG2324 equivalent) instead of 2SD1441. These types are not interchangeable because 2SD1441 contains an internal damper diode.
Symptom: Power supply dead, no pilot light.
Check diode D210. In the new model it is a plastic diode instead of ceramic, and several have been found shorted. Other power supply components (listed above) may also be damaged. D210 must be a fast- recovery type diode.
Symptom: No vertical synch, horizontal line in center of tube, possibly with deflection above or below line.
Bad part: Vertical amplifier (TDA2653A: large IC on heat sink). Sometimes fails along with power supply, voltage divider and IC303, as described above.
Symptom: No video but high voltage and sweep are present.
Check Q204 (npn), Q203 (pnp), or IC201 (7812; 20v in, 12v out). The front-panel contrast pot controls Q404 which biases the video drivers on the CRT board. Q204 and Q203 are powered by +12v from IC201. Failure of any of those three devices will cut off video.
Most 3192's have proprietary-numbered integrated circuits. By inspecting numerous units, we have compiled a list of industry- standard numbers:
IC201 7812 +12v regulator IC301 TDA2582 (rare failure makes power supply inoperative.) IC302 74LS221 function? IC303 7406 vert. and horiz. sync buffers IC401 LM723 voltage reg. IC for +5v; drives Q404. IC501 TDA2653A vertical amplifier. IC800 LM320T-12 or 7912 (-12v regulator) IC801 ? function?
D401 MUR815 high-speed rectifier for +5v supply. Q101 2SD836A power supply switcher Q201 2SD1441 power supply switcher Q203 2SA1127 (pnp) failure causes loss of video. Q204 2SC1685 (npn) controls contrast via front panel pot. Q301 2SC1685 Q302 2SC1685 Q401 2SD1441 horizontal output Q403 2SA777 Q404 2SD1442 +5v pass transistor Q405 2SA1127 Q409 2SC1685
Q604,5,6 2SC1789O Q601,2,3 2SC2258
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").
Power switches commonly fail in 3192's. The switch (part number 8233403) is available from IBM. Since 3192's are rarely turned off, it is practicable to remove a broken switch and solder wires between the circuit-board pads in order to return a unit to service temporarily if new switches are not in stock.
25-pin connector on back of 3192 CRT unit
1, 4, 5, 13, 14, 16, 25 GND 2 +12v 3 -12v 6, 10, 11, 12, 19 ? 7,9 +5v 8, 15, 20 NC 17 vertical sync 18 horizontal sync 22, 23, 24 video (3 colors)
1 +5v 2, 4, 6, 8, 10 0v 3, 5, 7 video (3 colors) 11 +123v 12 +65v 13 +90v 14 3-6v front-panel contrast control via Q204.