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G8MNY > TECH 03.09.23 10:31l 173 Lines 8455 Bytes #999 (0) @ WW
BID : 55038_GB7CIP
Read: GUEST
Subj: Marconi Counter Type 2432A
Path: IW8PGT<I3XTY<IZ3LSV<ED1ZAC<GB7CIP
Sent: 230903/0818Z @:GB7CIP.#32.GBR.EURO #:55038 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Nov 20)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I have repaired one of these old Marconi Instruments 560MHz Precision Frequency
Counters, Model No.52432-313Z.
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ >1 50MHz-560MHz, 50mV-5V max, 50ohm BNC
³ _ __________________ ³ Burst Mode, holds reading on sig loss
³ (_) ³ø8.8.8.8.8.8.8.8.:³ ³ >2 10Hz-200MHz 25mV-5V (250V 50Hz) 1M BNC
ɵ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ Æ» AF filter, <200kHz
̵ _ _ ƹ LF Multiplier, 0.01Hz Res to 13kHz (1Sec)
º³ (_) Ý Ü Ý (_) Û Û Û Û ± ³º Gate times 10S, 1S, 10mS, 1mS
º³ 1 2 ³º Resolution 0.1Hz,1Hz, 10Hz, 100Hz ñ1 count
º ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ º Oven Ref Output & Ext 1MHz 1V BNCs
ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ Supply 110/120/220/240V AC IEC.
I could not find a diagram for this "A" version, board layout & circuit are not
the same as the 2432 model, the 3 power supplies are all different. But the
counter and ICs are all the same, so a good starting point.
FAULT
"Not working", there was no -12V, caused by a shorted tantalum capacitor, &
that had taken out the T05 pass transistor. The +12V +5V rails were both
dangerously high, due to no negative rail on their control 741 op-amps! A
simple fault, if none of the chips were fried with the over voltage, it should
work now? But life is never that simple, as that was not the only fault! The 1S
gate range read 10x too low & other ranges occasionally read 0.6x low.
Sequence
Drivers Timers 40pin IC TOP PCB Up End Out Rigger
=============================================== Connection
FRONT Ý7seg JoiningÀÂÂÂÂÂÂÙ Hing out
Ý PCB|||||| /~~~~~~~~~~\ [ MAINS IEC
ÝLEDs ÚÄ||||||Ä¿ ³ Mains ³ [ & Volts
_ _ _ _ _ _ _ XTAL³ |||||| ³ ³ Toroid ³ Ä¿ REAR
BNCs Screened OVEN³ |||||| ³ \__________/ ÄÙRef BNCs
IN ÚÄÜÜ Pre-amps UNIT³ÚÁÁÁÁÁÁ¿³ metal frame o< Age Cal
& SWÀÄßß=============================================
- - - - - - - Pre-scalers * PSUs BOTTOM PCB
Pressing hard on the top PCB did change the faults, but a good solder up over
the 2 PCBs, did nothing! All these faults eventually proved to the large main
special counter IC, with it's 40 gold plated pins and socket on the top PCB.
Re-seating it MANY TIMES initialy cleared all the faults, so no blown chips,
from the original PSU fault. But it did not stay OK for long so I looked inside
the IC holder to see several broken socket fingers! So I soldered the IC
directly in. (well you would never get a replacement IC)
A year later another fault appeared, the Ovened 10MHz Ref Osc stopped working!
An aged rubber sleeve (conducting) around the Trimmer C was the fault, after
much poking around.
HOW IT WORKS
The 2 inputs both see pre-amps with a common AGC (90dB LF, 54dB UHF) & are
relay selected, to feed a special gated UHF ö10 pre-scaler IC, then into an HF
ö10 pre-scaler, and last into a ö2. The resultant ö200 feeds the slower special
40 pin main 5.5 digit counter IC. The pre-scalers also feed 9 BCD data lines,
read during gate reset time, for the additional (LSD) 2.5 digit information to
make up the 8 digit read out.
TB Gate Gate time select
ÚÄ<ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿10m 100m 1S 10S LF
³ Reset/read ³ v v v v v
VHF-UHF ³ ÚÄÄÄÂÄÄÄÄÄÂÄÄ<ÄÄ¿³ |...|...|...|...|......DP......
1)fuse-Preamp__ ÚÄÁÄÁ¿ÚÄÁÄÄ¿ÚÄÁÄ¿ ÚÁÁÄÁÄÄÄÁÄÄÄÁÄÄÄÁÄÄÄÁ¿ \
ÃAGC \_³ö10 ôö10 ôö2 ÃÄ>´ MAIN 5.5 DIGIT Ã>DRIVERS->8x 7seg
2)ÄÄxÄÄPreamp__ ÀÂÂÂÂÙÀÂÂÂÂÙÀÄÂÄÙÚ>´ COUNTER IC ³ LED display
AF LF-VHF A\\\__B\\\__C\__³ ÀÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÂÄÙ
Filter BCD data ³ | |
ÚÄÄÄ¿ ÚÄÄÄ¿ ³ | À-->Overflow LED
Ref 10MHzÄÄ>Ä´ö10ÃÄÂÄÄÄÄ\___³ö10ÃÄÄ>ÄÙRef |
Osc Oven ÀÄÄÄÙ ³ ÚÄÄ | ÀÄÄÄÙ 100kHz À--------->Gate LED
³ ³ ÚÄÄÁÄÄÄÄÄÄ¿
Int)<ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ÃÄ´Auto Ext Ã----------------------->Ext LED
1MHz ³ ³Ref Sence³
Ext)>ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÙ
The main IC determines the TimeBase gate time & is feed with 100kHz reference.
This is derived from a fairly accurate & stable 10MHz Xtal osc & buffer in the
electronicaly controlled oven.
The fast reading LF multiplier range (a useful LF feature) gives resolution
down to 0.01Hz in 1 second! It counts reference clock for a few input cycles
(100kHz Ref & Gate swapped) and then the reciprical is calculated & displayed.
But it only works up to 13kHz!
TESTING & CALIBRATION
The +5V rail has a preset for setting it to +5.10V and the +12V rail follows.
The -12V is independant.
Input 1 VHF-UHF, pre-amp tends to oscillate @ 400MHz with no input, and a
lockout preset (like a squelch) kills the erroneous reading. When adjusted well
it managed >810MHz @ 1V input (5V max=250mW).
Input 2 AF-VHF, pre-amp has a Schmitt trigger, & setting the bias preset (DC1)
well, is very important for best sensitivity, & good to VHF. It managed >320MHz
@ 1V input.
Both pre-amps share the same AGC preset with 6V DC set testpoint (no signal).
Reference oscillator calibration is done after at least 15 min warm up with the
rear multi-turn preset. Compare the 1MHz output with an off air locked 1MHz on
dual beam scope (while counting something), or just count a reference source.
Overflow LED lights over 99999999 count, but the display is still accurate for
>8 digits.
OVEN STABILITY
Square law Time-Hz plot of a 10MHz off air locked reference.
Hz _
+20´ Þ 'ú Fast Oven - - Longer term Oven & PCB warm up heat drift - -
+10´ Ý ' Heat Up Heater &
5.0´ Þ ' Overshoot Thermisitor
2.0´ Ý ' Delay Oven Cycle
1.0´ Ý ' .ú''''ú. .úúú.
0.5´ Þ ' ú' '''' 'ú...ú''ú. ..
0.2´_Þ_ _ _ _ú _ _ _.'_ _ _ _ _ _ _ _ _ _ ''_ 'ú''ú.ú'úúú..
-0.2´ Þ , . _ -
-0.5´ Þ ú _ -
-1.0´ Ý 'ú.ú' _ - Warm up Drift Compenstion diode
-2.0´ Ý _ - Correction offset mod for quicker accuracy.
-5.0´ Ý- I------------------------------------------->
-10´Þ
-20´Þ
-50´Ý
-100´Ý____________________________________________________________________
0 0.5 1 2 4 8 16 30 60 120Min
Longer term Oven & PCB warm up heat drift
In use it gives repeatable accuracy of < 2/10^7 ñ1, or less than ñ2Hz in 10MHz
after 1 min warm up! But 1 hr for 20x better stable reading of < 1/10^8 ñ1, or
less than ñ0.1Hz in 10MHz! (ref to an off air source)
The internal reference is 10-100x more stable/accurate than a non-ovened Xtal
in a cheaper counter, or for that matter your rig !
MODIFICATION. To reduce the warm up drift of above in a few mins.
+12VÄÄ750RÄÂÄÄÄÄ¿ ÄÂÄ+12V
_³_ 10K *1N4148 43K* Cal Voltage to
6.8V /_\' Cal<ÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄ´<ÃÄÄÄÁÄÄÄÄÄ>Varicap of ref Osc
³ Pot *4u7 === Inside Oven
ÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄ
Put *4u7 near oven connections to reduce stray Counter input pickup affecting
the reference. Take plastic cover off oven & put *diode and 43K under the foam
insulation.
OVEN LED MOD. This shows when Oven is warming up.
+12V >ÄÂÄÄ5R6ÄÂÄÄo Heater
³ ³
ÃÄÄ´>ÃÄ´1N4001 The main PCB +12V track is cut feeding
³ ³ the oven & components soldered to the
e\³ 4K7 tracks & nearby ground. A wire is threaded
PNP ÃÄÄÄÄÙ from the 2K7 to the front bezel and a small
/³ // LED -ve lead clamped under the metal surrond
ÃÄÄ2K7Ä´>ÃÄ¿ under the Overload LED. Care must be taken
4K7 Á to avoide other components!
Á
See my other tech buls "Watson 'Hunter' Counter Mods", "PIC Freq Counter Mods",
"Old Venner Counter Type TSA3334", "198kHz Off Air Standard", "Off Air Lock for
Ref Osc", "Calibrating Frequency" & "RTT Comms Test Set".
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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