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DEC-12-HVRTP-A-D

December 2000

10 pages

Original

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Document:	dec-12-hvrtp-a-d
Order Number:	DEC-12-HVRTP-A-D
Revision:
Pages:	10
Original Filename:	https://svn.so-much-stuff.com/svn/trunk/pdp8/src/dec/dec-12-hvrtp/dec-12-hvrtp-a-d.pdf

OCR Text

RON
x

H"mm“3
_.

:
"

m
W
;I;;

'"f 1. 1NTRooucrroN
VR14
When servicing
a

V R20

Display,

relatively

it is

easy to

_..

__.

replace faulty component and obtain 11111111131
3

“

the screen. However, this method of maintenance usually fails to eliminate the problem that caused the component
'

‘

basis. The purpose Of this document1s to provide
I.

fai1ure; Until the cause is found and corrected, fuses and transistors may have to be replaced almost on a weekly?

‘

‘I
1'

The 4111ccmost frequentcauses ofVR14/VRZ 0 failuIe are:
Overheqted

11011111111111.1101,

construction (bad
Arc1ng
CRT.

(3011115010? CHIEFS faulty pins msufhcrent therm
leompouud)

b Faulty

farrure

procedures to deternnne thecause of component

of the

"-1

The remarnder ofthis docun1ent provides procedures used 101 determining and correctrno the causeof- VR14/VR20 .‘
below
11111111. There specrfic procedure for each one of
the three symptoms lrsted

is a

”

Procedure

Paragraph Ne

Symptcm

a-‘-"

‘

”

Fuse

blown and 2N4399

2N5302

collector and emitter. 1,

transistors

shorted between

fails to produce intensity-7":337711111 111/682 W683
have
the
both
pulses. Also,
power transistors
equipment may
and
a
fuses bloWn and/or the +22V at 1.401! levei

[1,4- B

3 g»

1ntensrty board

*C‘

4,
.

=4 4.

’l

,4.4

Blown fuse

only,no

other

componem fa1lure..4

Procedure A includes a nrethod for reworkingthe deflectron heat sink to proude better heat drssrpatron A more -‘
detailed eXpiananon of- this rework1s presentedinParagraph 45.

4’

‘

Fuses and transistors do not rnaifunction Without a reason Transrstors normaliv short

overheated. This overheating
34a.
.

There
.1111

occurs if

is inSufficient

11144481712121

power supplyvoltaees

‘

I”

out

because

they become“

‘

’
'

compound under the power transistor.

are

higherthan 110111111,111e1¢11y overdnvmg the

power transrstor

The. deflection inputsionals have high frequency osrllatrons Wthh overheat the transzstors
or

”I

.2 VS," 'd.

The fan-fails .t‘o'reach {proper operating speed.vV

V
S

1 The

beamis deflected off thei'S-ereen for anextentled period-of tirrieg
rmDmperly mOunted tothe
.f. Q. The
4442 to loose or broken socket orloose
threaded insert.
'7_
hold
screw

transistor is

due

heat

’

transistor

g.
,

down

is to be used

for replacing the transistors and fotcorrecting the
V

Vvieftoff

the malfunction
S

_
.

CAUTION

.
.

oniy Motorola tranSistoIs and either Dow Corning No 346
or Wekefieid No.126 thermal compound. EEC part nembeIW-R

‘

Use

7' be replaced. Use an ample amount; of white thermal
VT] compound; be sure that the teams" stor insulating washerIs not

cause of

the 2N4399is shorted, the 2NS302 on the same side must also

V
h

(ROWER TRANSISTORS MUST BE REPLACED IN PAIRS if’j‘

_
p

fuse and defectiRe transistors

Replaee the

The emitter protection resistor has drifted

The follOwing procedure

‘

sooszss oo Nor Use

’

‘IV‘: .1,

V,
'-

‘

COMPGUND?

sILtCON

CAUTTON

’

CLEAR

.
_

the

wheh reRleemg

mOUHtmg
f transistors. To do soVwVill strip the socket anti render theheat
.Isink totaily useless. "The ScreWSshould be firm, h-tithot
'V‘excessively tight. if one of the mounting inserts become loose,
replace the socket, DEC part number 12-81288, of the 444-244
assembly, DEC part numbers
70-7082 (Deflection; and»
708{}
Sapply).
'78(Power
“9*

overtorque

screws

,
4
'

,--

‘

2
'

Check the 0.19 emitter resistors
on the transiStor sockets for horns,
they Show evidence of overheating or do not measure exactiy
0.152, Vdeflection and power supply heat sinks)
__'

mounted

‘

carefttliy

Remove the X and Y deflection boards arid

measure

indicated. Also, if. these voltages shift while

'psttpply

faultis unheated

both the
--

V-

pins A0i UV

are

being run a power

’

y
,

power supply fault is

diagnostic programs test patterns
.

1.0,V

them (Check

replace V-V
7V
the powersepply soltages
22V

(+22V) and A01 -K (-2 2V). If either of these voltages exceeds

cLaeks, or discoloratror If

;

CAUTION

power supply problem exists and is not 4444-44442, the
Will
probably failagain in the
44444.4.
power transistors
17":4. [Cheek
the G836 regulator card 011 the7007165 to ensure all ECOs have been incorporated
_

near

.
p

”

b.
.

“

If a

'55 f. [Z 53;. [Ca

R9 ans

R24 should be

(See VAC:
Figure

2209, (261th

R10 and R27 should be

1444 440415052

R2 and R17 should be 1. 78K

l% resistor,

not 1. 62K 1%. This

lowersere +24V

to +22V

1.;5

z‘;32;,Tg»:;«py7w,-jg¢x,».ang lagj<*»,i“5.j?.-g*V4W40fl

_Hg,»,~,T_

“ECO#3T

-"
'

‘

«xvi:

TV";~5_I

IIIII
_‘

2 :1+4}§§§}* 3

Figure-1

[BETWEN

,;-,._g.;

707165wa‘éx‘aegfizaszm

4 JTf‘GL TRANSISTOR

”SW vA178K3

HEAT-

g.t;';%

As gmbly

SINK

‘i

f‘.7HTI
2 -03 4

fPLACETHFRMA¢.COMP0UND *-”H’7jeni‘ng7I,"}.¥16353_gfigT"TAHffjfofj{f7O7165f

“.mf;fECO#3' .17_Tonyu4w

_}v4w
2 cm

5].

power Supply voitages' drift of ivafide'r; change; Q2(2N49120),6rl Q4 (2134923.), E1009), add-E2 (70,9)

obtain a new 7007165 regulator. Make Certain. that the board (G836)1n the new regulator is revision

D or higher Rewarked revision B beards with a
decal are acceptable. Make certain that the
and 6 incorporated
have
4,
2)._
2, 35
(Figure

ECOS

A225

beards

ECO #2 R29 and R30 (2252) replaced by wires {Reduces runaway)
ECO #4

R1 and R2 are 10K 1/4W {Reduces gain sensfiwny)

ECG #5

C1213 100 pf (Prevent3 internai oscillations)
1W (Prevents internal latcnup)

‘

ECG #6 R19 is 200:2

‘

Ww5’E-Co45 {Oo'pf
‘312.
__

EC0~#5.

I
.

“

5010434

S 93 A22!

m 2 R2
103 124w

SHOULHI GE.

3 1K.
'

3":"97-1-4:1‘2—6333725

‘In-

order to inc1ease heat- dissipation for the power transistors, ECO #v’Rl4-15 rnust be installed This

ECO consists of physically interchanging the inside section (X) of the deflection heeat sink assembly With
the outside section

(Y) This is done because the outside section receives setter air fies Since X
’

generates

heat

coolingair.

.~--~

-HH__A___

._.

F011“ 50 Hz

NOT E

’”””'rfii.pygfif”gfhua‘

11:11:13,333 for ECO #VRlélé-TS; 111111 ECO requires

13-33-1131: frequency.

’

.‘fI-f

739.7}.

cooling at
7

interchange accomplished by unscrewingthe end plates of the heat .1131: assembly,eschaflamg
is

heat sinks

that X heat sink

153 on

‘

’

the outside,

and than

the endplates

the

replacing

the line

circuit must be complete.
Heating of the poWer transistor 3lso be reduced by decreasme the high voltage 111erebyreairing less
used and

.
.

Before reassernbly. removethe thermal cutout on the X heat sink and replace it With a6- 33serew to
hold the terminals on the inside. Place a jumper plug across the
thermal cutoutleacis because theCutout ff;
13110 longer

‘

"
'

Figure 3

I. that 7-blacled fans be instaiied to insure adequate

,._

5 and shown111

given Paragraph

33333

I. The

33311111 procedué'e. for field rework of the deflection heat sink. Vii-11"

“

’

The
folloWing onlyrepresents the basic pocedere The?
'3

’

NOTE

Y»-

than '1’, Xrequires more

3‘

can

current for full-scale deflection. The high voltage can be reduced by removing, the AC inputWires
,
115
311d
tap
them to the 100
Vac

tr3nsformer tap

This step is V3 aid

only. for the V9.14

voltage input wires

011

VRZtlis airea ..y

than t1e

loWer

Vac

Once the Wires have been changed the X and
*

current

reqmrement

ZINOTB that ECO T56836- 5

315 Vac

and from TBZ-l

high voltage on a VR14.

rnethod valid if the VRl4 wired for 131111131240 O!
-4
to
VMove the red
high Voltage supply input Wires from TBl l TBl
The followmg

to T833

gain must he readgusted to compensate for the lower-3.1.7
.1.

(See FlgUTe 1) chances the Value of ICSTSTOI’S +23/§V to +21 5V thereby:
'

reducing the

deflection heating

Make certainthat all power transistors 11113531113133: thermalcompoend lf’lthe failed
1/32mch
'rlrthen the other transistors also probably are dry All mating surfaces must

transistor is dry,

have

layer

’

-I

thermal compound applied with flux brush. No bare metal shoold shoe].
Check for oscillations and/or “fuzz” the input sighal waveforms If these are preseru overheatino 9ij
a

on.

the deflechon components may OCCUI.

the and 33113311011 boards
X

Remstal

_-‘

3‘

Do not chance high
because
the
high voltage or: a
the VRZQ

_
_

V31:

connecting

from

the

3,35

'3‘;
_

:~-,.

’jé’m
BACK.

'DEFLECTzo

HEAT
SINK
’

‘33

PLAT-E:

‘

"‘~g-T§-F'* SINK DEFLECTION"
'

‘-

HEAT

‘”:7.%IN.~BACK_PLATE

;.':

‘

_3—'f:.\
.

‘

’HEAT'SINK

;i;f}’.:2M439

’3‘

“{‘2Ns3Q3£*if

[CABLECLAMP

i/fga:

‘

CONECTOR

”MATE'N'LOCKj

,15

PIN
.

‘k.

‘43

Measure the

,.>

.‘21 Sip,i. They should be approximately +2 5V and +2 .OV,
reSpectiver. These voltages indicate proper operation
.uf;”flf
for lower left corner deflection for PDP-lZ Operation F or PDP- SE/PDP ll operation, the yoke sample {It}
return wili measrlre 0 (IV on both pins thus indicating preper center screen
deflection. Therefore adjust

A >29
1

yoke serrrple returns (pins A02-A and A03 A) withnoinput signals (cable disconnected)

-:_av

the posrtromno potentiorneters for +2. 5V and +2 CV to load down the positive power supp{y
TRefer to Figure 4 Measure- the base—emitter voltage dr0p in the power suppiy heat sink aSSembly

supply is being used it should indicate full drop, 1. 2V, while the negative _,V
7
supply shoui(1 indicate only standby drop 0 5V if the positive suppiy measurement indicates 24V 3'!
7
is
then one of
Replace both 2N4399 transrstors‘ _'
the

'*.’_IIB€C’41156 Gilly

the positive

;
'

'base-toemitterchop,
2N4399transistors open.
While measuring the approprrate YOke turn, adjust the position potentiometers
re

I}.

the X and Y

deflection boards for2.5V and -2 0V deflection (upper right corner deflec’non). Then, again measure
';'the base emitter voltage drop for the negative supply It shouid then be 1.2"." and the base~ernitter drop
the
g,‘
potentiometers to
values
for the
should be 0. 5V

,
7

positive supply

their original
Return position
CAUTTON
if the position potentiometers
adjusted for combined
of
than
veitage
LthV (10areperes) the respective 11C
fuse
blow.
.

._,

are

,.
,_

9»

"_ f

'_-7j_

1rid-{i

7‘057165_(o»8ss?Assw

0' 0

._'-

.1.

.-;

r‘

.h f'-

P21

no.

Ia¢

//
’

REGULATOR

.-2

94»,

;

0 020

\NEo-ATIVE
~-w;_;;,;rp.

—

»'

POSITIVE_*= REGULATOR

BASE—emrrsa

_
.7

BASE—EMITITER

7T'T2-0335C,TL.{39
q.

T‘- 7

and thus the VV682 intensfly board
CRT the cathode,
O.
p. .
9._ 0‘9Q
2:3” 0
E2. 012

Wi‘ien a display
arcs,
H
53' "- O 1 ('3 DD :3 _mW U3 0 H (DO Q4 (D r..-:23.“ (D O4 (D 2

0%
I 7that
'

'ofan

Fij

Figure 4 _,Base~EI_nitter Voltage :‘Dto-P. Test PO‘int‘Loc'atiQH»

receives

r‘+ {‘33 (D

longer function preperly It13 also

overvoitage condition

ooooo

:3 9‘

possible for
~

U3 0

9.. O m on- CD

'L4

power transrstors

the overvoltage surge The G835
9. 3. O .0 £13 "C3 :0 3 H‘ O 11-1U) Q.):3 Cl. H

Q.
L4
é-i§”
to short
from coliector to emitter because

in"

(U .0 ourH

€ :3

1:?

”O MW

'_ ff
-»

diffiCult part 0ftroublesliooting YR14 that has malrunctioned becat.se Of anarcing CRT findingall oI

The’most

the components that have failed

be come damaged. Some
etimes these failures are very subtle For example, the

operational amplifier on the 6836 regulator can become partially damaged hilt appear to function
correctly However, in reality, the i22Y is not regula
and eventually climbs to 4OY, thereby oI'erdriving the
ed
Which
falls
then
jdeflectiOn power transistor
MCl709

‘

.
_
_

‘

proCedureIs to be used when troubleshootingYRl4 that has failed because ofan arcing CRT:

7‘

The followi2g

1411' Replace fuses, poWer transistors, and any other com ponents that have obVioust failed USe only
Motorola transistors and use sufficient thermal compound (referto Procedure A, Step 1)

2. ifReplacethe 709 operational amplifiers on the G836 regulator board
I

“

_' 3. Replace the

arcing
,

’

PRoeenURe C

When

dc Me has

—

---

blown, it isUsuallI because the power supply has been subjCCIed to CurrentoI'erload. HoweVer

externally generated oveIload,

or a
Fanlty connections in the YRl4, powerhighup problem

.
.

The followingproceduIe to be used these cases
j
Replace the fuse and obtain
pictur the display
In

result of failure of internal components (transistors), then the problem is due to an

as a

’

_-_

;

5 if a fuse blows but not

CRT Ivhen the specrfic YR14being repaired hasa prevroushistory of failures due toCRT

1-,,

2, Y
‘
.

II,

Rernove the top screen on the YRl4 and, While pietIIre is displayed shake and Wiggle thefeur cables
and associated connectors coming into the G836 regulator
{the pieture breaks under this condition it indicates a fan ts? pin or connection that *nustbe,
up

f. If"

repaired,

‘

If a be d connection

interruptscritiCal Iroltage, the deflection amplifier deflects the beam off screen. and”.

blows

the fuse

31f shaking

fails to isolate the problern than one two problems
of

exrsts

The input deflection Signals are intermittently excessive, thereby drIVIng the CRTbeam mi‘
and blowing
the fuse.
screen
~

-_
,_

b, A pewer latch-up poblem eXists

4.3.1} Cheek the computer D/A converters for intermittent incorrect outpUSIYake
or

on the

oscillations

"
'

{7'

ceI tam

D/As.—

that there no;
are

power latChaip problem

5 -.-;l Check for:a

When power isturned on, the defleCtion

amplifier settles its normal operatingconditions Howev if:
to

‘

'1'

f ;

.,r

poWer is subsequently turned off and immediately turned on again (within 1/2 second), the deflection Riff]?
7' amplifier may receive the power supply voltagesIn such a manner that the deflection amplifier saturates
5
prevented
driving the CRT beam off screen. The deflection amplifier is
recovering unless
or
one
downfor

"
-

seCond longer

powered

then

frorn

power latch-up problem occurs, it is wbrse at low line (110 Vac) If the YR14 is lefton in this
the
other ~qu
latchup
the
5‘
mode, deflection amplilrersaturates and blows "22Y,_10A fuse However
harm done

If a
_.

*fzftfl'hMakecertain that resistorRl9 onthe A225is 2009. rather than
changed by EC03% 225 6 toprevent a latchup problem
-~

if the D/A converters in the computer deliver

incorrect analog

2709.

(see Figure

The resistor was '1

2},

N“._.2_._-

~._....4~'-u.—“.mwn.w

‘
'

ma..
.1

the d15play X and YlantLS SV'
'

voltages to

the beam Can be deflected off tle screen causrng a fuse to blow which protects the

_.
__
_

TV-Vij- .'

deflection amplifier
Thiscondition may exist in computers that uSeseparate precision +lSV povver suppl’ies (such 13111117”?
V- i

-«

EDP-12 computer}. Some of these supplies latch-up in current fold- back when turned on, causing the

+15 Vdc to go to 0V This in turn causes the D/A conVerters to deliver ~12V instead of the correct
VOItflge An ECO (ECO #A615 6)111 the PDlP- 12 places zener diodes on the output to clamp the D/A to 21 1- V.
"safe Value under these Conditions. Other D/A subsystems may or
1mm
this
may not

._
,

for. further information

check the apPIOpriate

have

output

‘

VP‘OteCllOn
DEC-O LOG
5 FIELD REWQRK 0i? DEFLEETION
SINK
described111
The. deflection heat sink can be reworked to previde better heat dissipation for the pewertransistors as
.

’

HEAT

-1

Step 6 of Procedure" (Paragraph 2). The X heat sink,1.vi1iCh generates more heat than the Y heat sink, is physically
exchanged with the Y heat sink with the remit that the X heat sinkis near the Outside Of the VRI4 chassis in this
the
procedure
position it getsbetter air. circulation for cooling
of reworking he

Sink assernbly (sect:rig-are3)
_

The following

\d‘lfim fip

if you 1111111: that the heat sink may have already been

heat

~_.

V
'

i‘

moved to the outside

'_5‘V»V_the V3.14 chassis.

3132123156 l/2—inch back plate aflatsurraceWith the tWo mountmo screws (used for securing heat S1nk)VVV"HV.
facing up and half—circle cutout facing the bottom.
heat sink (identified by grey wire on transrstor collectors) tothe [21116111back-7
'fVSecure the X deflection
the
6-32
X
1/4 screws;
Make certain the 2194399 transistoris on bottom
plate, using tvvo
Place Nil-inch mounting block onother Side of the X deflection heat sink
331111 thecable clamp screw
6the
,'_V'hole Vfaci’ng top. Secure 1vithtwo 32 X l/4Screws
secure the Y deflection heat sink (idenufied by violetWire transrstor collectors) to the opposrte side
.‘cVP‘ofthe assembly, ensuring that the 2N4399is on the bottom
2' "sec-1111:the cables frorn X and Y
of the l/4-1nc‘1 front plate With cable _'
deflectionheat to
'

‘

’

.
V

‘

Vijf'ljclarnp

and6 -32X 3/8 screst.

1 :
.

sinks thetop
.

plug

“

To complete the AC line circuit, place jumper
Vconqectcd to theplug for the thermal cutout
Replace deflection heat smk semoly1n the VRl4
a

the 2—1111:

(70070063) in

_
.

Connector

that

Was

V
_

_
3

Removedeflection heat sink asspmbly Vhe
W14
{mm
Remove 6-32 /83
X screwthatsecurescable clamp [4-inch1 front plate
iii-Remove ight 6-32 X 1/4screwsthat Secure X and Y heat sinksto front and bask plates
-V
hOVe
.VVLRemovethennal cutoutfrorn X deflection heat 31111: and place 632 X 1/7 panV headSCVBVVVVVVLV the.

.9.
.

provides method
-

modiued and you Wish to check to be sure, adjust the X.
Position tn 0V Yoke return and feel the outside {leflectien
transistors. They should feel cool. if one remains warm, the X
f heat sinkis on the inside,
and must be
of

M.h..r.._._._.'_..._..