148 lines
5.8 KiB
Modula-2
148 lines
5.8 KiB
Modula-2
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Newsgroups: rec.radio.shortwave
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From: mb@sparrms.ists.ca (Mike Bell)
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Subject: PRO-37 Scanner Modifications (Long)
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Date: Tue, 24 Sep 91 13:32:11 GMT
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MODIFICATIONS FOR THE PRO-37
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----------------------------
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The disassembly instructions are based on the excellent PRO-34 instructions
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provided by Chris Scholefield (chriss@mid.com). I have added my own
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comments.
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First of all, what modifications are possible?
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----------------------------------------------
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The PRO-37 uses a diode array to l tell its microprocessor what model it
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is, and thus which frequency bands to allow and what channel spacing to
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use. European and Australian models have full 800 MHz coverage (at an
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unknown channel spacing) and a VHF-Mid band (68-88 MHz) rather than a
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VHF-Low band (30-54 MHz).
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The Canadian and US models differ in the amount of care taken to reduce
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EMI. The Canadian model has additional screening, and one or two other
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minor component additions to achieve this. Therefore, if you have the choice,
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the Canadian model is preferable to the US model.
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Changing from VHF-Low to VHF-Mid band coverage requires many
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component value changes (and realignment of the appropriate RF stage).
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Given that the PRO-37 uses SMT technology, it's not worth trying.
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(You can change the diode array easily enough, but just don't
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expect reasonable performance!)
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The only sensible (straightforward) modification is the restoration of
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full 800 MHz coverage on Canadian and US models. The ranges restored
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appear with a 30kHz channel spacing - which just happens to coincide
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with the N. American cellular telephone channel spacing. A remarkable
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coincidence.
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The modification described is therefore applicable ONLY to Canadian and
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US models. (European and Australian readers could always remove
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800 MHz coverage if they wished:-).
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You will need:
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Soldering iron - with a fine point. (The components desoldered
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and soldered are not SMT, but ....)
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Desoldering tool - to remove excess solder
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Philips screwdriver - if it fits the screws on the back of the
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case it's the right size.
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Small pliers - bending component leads while unsoldering
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and removing hexagonal posts
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Earthing wrist strap - strongly advisable with CMOS components.
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(Static can cause premature, if not immediate
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failure of components). Wear this at all
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times.
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Small screwdriver - for prying components etc.
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Experience and confidence in working with modern electronics
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A couple of hours without interruptions...
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Instructions
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------------
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0. READ THROUGH ALL OF THESE INSTRUCTIONS BEFORE STARTING!
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1. Remove the battery
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2. Remove the antenna
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3. Pull to remove squelch and volume knobs
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4. Unscrew the 4 screw on the back of the case
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5. Separate the case beginning at the battery end and work over the circuit
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board and knobs at the top
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6. Unsolder both connections to the antenna - ground can be bent away and the
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centre has a link to the board
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7. Unsolder the two power switch links at the board end
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8. Unsolder the ground connections to the metal shield
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9. Disconnect the two connectors to the squelch and volume controls
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10.Remove 4 hexagonal posts
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11.The top board may now be removed by separating it gently from the
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connector on the adjacent board
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12.Remove 3 screws holding the shield in place
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13.Lift the shield to separate it from the lower control circuit board
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14.Identify diodes D12,D13 on the control board
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15.EITHER cut the diode D13 and SKIP to reassembly OR continue to desolder diode
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16.Remove last two screws and remove control board. Take care not to
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dislocate the KEY LOCK switch when doing this.
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17.Unsolder screening from side of control board near diode array,
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and bend back out of way.
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18.Unsolder and remove diode D13. Keep it somewhere so that you can replace
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it if required to do so by US legislation.
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Reassembly is the reverse of the above procedure.
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If you performed steps 16-18 CHECK REALLY CAREFULLY that the metal part of
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the KEY LOCK switch is in the right location. (Otherwise, you may find
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yourself having to disassemble the whole thing again - I know, I did!)
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NOTES.
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1. One must exercise great caution in the procedure. Check that no flakes
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of solder get dropped on the boards. Take anti-static
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precautions by doing the work on a mat and wearing a wrist strap. Do
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not make any adjustments to the upper analogue board or bend any of the
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other wire links on it, which are tuned circuits.
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2. Another caution is that doing any of the work will probably violate
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any warranty you may have on the scanner. Might be worth burning the
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scanner in for ~150 hrs before attempting this to reduce the risk of
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a latent component fault appearing after you have made the modification.
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3. YOU PERFORM THE ABOVE PROCEDURE ENTIRELY AT YOUR OWN RISK. You may
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wish to obtain a copy of the PRO-37 Service Manual from Radio Shack
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before attempting this. (Cost about $20 - well written - just wish
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I could afford all the service gear required!)
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4. If you happen to find out what adding D14 does (another difference
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between N. American and European/Australian versions), I'd be
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interested to know. It's not mentioned in the service manual. I think
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it could affect 800 MHz channel spacing - any info on the European
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Australian PRO-37 specs in this area would be appreciated.
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5. If you found something wrong in the above instructions, let me know
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and I will try and post an update.
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6. If you found all this helpful, help someone else and donate $5.00
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*today* to your favourite charity.
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Share and Enjoy!
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-- Mike -- <mb@sparrms.ists.cao
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