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If it has a mb3756 in it, it is old and worth fixing.
Restoring as many 148's as I can get from Hamfests - lol.

Here is where I would start:

1) Check pin 9 on the 8719/pll chip; it should be ~8v all the time. If you aren't seeing 8v; then the regulator has failed or there is a shorted electrolytic cap(s) on that 8v rail. Old radio; then old, dried out caps are a commonplace issue.

2) BTW - Replace all 10v caps in the radio using a 16v or 25v with the same capacitance value, as a rule.

3) Check to see if the Cobra Service Bulletin #1226 was done to it, which adds a 18v zener diode near the voltage regulator. That diode may be faulty or probably not even present. I do that SB mod to all 148/142 and all Uniden chassis that have the mb3756 regulator. This doesn't fix anything, except keeping that regulator from failing. That part is becoming more hard to find, so it would be wise to keep it working.

4) Then check the VCO voltage as the Service Manual describes.
http://www.cbtricks.com/radios/cobra/148gtl/graphics/cobra_148_gtl_sm_pg48_pg63.pdf

<blockquote data-quote="Robb" data-source="post: 482130" data-attributes="member: 8446">If it has a mb3756 in it, it is old and worth fixing.&nbsp; Restoring as many 148&#039;s as I can get from Hamfests - lol.Here is where I would start:1) Check pin 9 on the 8719/pll chip; it should be ~8v all the time.&nbsp; If you aren&#039;t seeing 8v; then the regulator has failed or there is a shorted electrolytic cap(s) on that 8v rail.&nbsp; Old radio; then old, dried out caps are a commonplace issue.&nbsp; 2) BTW - Replace all 10v caps in the radio using a 16v or 25v with the same capacitance value, as a rule.&nbsp; 3) Check to see if the Cobra Service Bulletin #1226 was done to it, which adds a 18v zener diode near the voltage regulator.&nbsp; That diode may be faulty or probably not even present.&nbsp; I do that SB mod to all 148/142 and all Uniden chassis that have the mb3756 regulator.&nbsp; This doesn&#039;t fix anything, except keeping that regulator from failing.&nbsp; That part is becoming more hard to find, so it would be wise to keep it working.4) Then check the VCO voltage as the Service Manual describes.<a href="http://www.cbtricks.com/radios/cobra/148gtl/graphics/cobra_148_gtl_sm_pg48_pg63.pdf" target="_blank">http://www.cbtricks.com/radios/cobra/148gtl/graphics/cobra_148_gtl_sm_pg48_pg63.pdf</a></blockquote>

[QUOTE="Robb, post: 482130, member: 8446"] If it has a mb3756 in it, it is old and worth fixing. Restoring as many 148's as I can get from Hamfests - lol. Here is where I would start: 1) Check pin 9 on the 8719/pll chip; it should be ~8v all the time. If you aren't seeing 8v; then the regulator has failed or there is a shorted electrolytic cap(s) on that 8v rail. Old radio; then old, dried out caps are a commonplace issue. 2) BTW - Replace all 10v caps in the radio using a 16v or 25v with the same capacitance value, as a rule. 3) Check to see if the Cobra Service Bulletin #1226 was done to it, which adds a 18v zener diode near the voltage regulator. That diode may be faulty or probably not even present. I do that SB mod to all 148/142 and all Uniden chassis that have the mb3756 regulator. This doesn't fix anything, except keeping that regulator from failing. That part is becoming more hard to find, so it would be wise to keep it working. 4) Then check the [I]VCO voltage[/I] as the Service Manual describes. [url]http://www.cbtricks.com/radios/cobra/148gtl/graphics/cobra_148_gtl_sm_pg48_pg63.pdf[/url] [/QUOTE]

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