Re: A/R II voltage running up

Kick myself... Cheap DMM reporting voltages too high. My other DMM reports
everything A-OK... Arg... Even running low: 4.75vdc. Used a PC supply to
verify. Cheap DMM reports 6.25 VDC and the R/S DMM I bought in 1985 reports
5.125vdc.

How do you calibrate a DMM? Oh well, at least I learned something... New
LM305 and all is well. I bought some equivalents for $0.25 each. Anyone
interested?

Kirk S.
----- Original Message -----
From: "William Boucher" <boucher@mnsi.net>
To: <vectorlist@vectorlist.org>
Sent: Sunday, March 22, 2009 10:09 PM
Subject: Re: VECTOR: A/R II voltage running up

> The 0.1 ohm 7W resistor (R24) is not the issue. It likely looks like it
> is reading high due to the multimeter lead resistance. Hold the leads
> together and read that value (call that the zero value), then read across
> the resistor and subtract the zero value.
>
> Obviously enough power is getting through R24, in fact, too much. Check
> first R29 and R30, the 10 ohm, 1/2W resistors. They are what fail most
> commonly due to bad edge finger contacts (they burn).
>
> Another possible and probable problem could be that either Q2 (TIP32) or
> Q3 (2N3055) is shorted such that the regulator IC cannot turn down the
> output voltage because one of them is leaking.
>
> If those parts are okay, check that the sense leads are okay (J7 pin 3 for
> +5V & pin 2 for gnd). Next check R7 (7.5k) and R6 (3.9k). These two
> resistors in series with 1k pot R8 control the regulator. Check R3 (33
> ohm) and R1 (270 ohm). I forget off the top of my head what they do for
> the regulator. It is entirely possibly that the LM305 regulator (Q1) is
> shot. Bob Roberts supplies them but hopefully it'll be something simpler
> than that.
>
> If the chips on the main board were really running at 6V... then may the
> force be with you.
>
> William Boucher
>
>
> ----- Original Message -----
> From: "Kirk Spradling" <kspradling@kc.rr.com>
> To: <vectorlist@vectorlist.org>
> Sent: Sunday, March 22, 2009 10:03 PM
> Subject: Re: VECTOR: A/R II voltage running up
>
>
>> Pulled one lead of ALL resistors on the +5vdc side and found that the
>> .1ohm 7watt 3% resistor is showing .45ohm resistance. Does this need to
>> be a wirewound resistor or will a ceramic work ok? I've seen several
>> different types, non-inductive is more expensive.
>>
>> Recommendations?
>>
>> Thanks!
>>
>> Kirk S.
>> ----- Original Message -----
>> From: "Kirk Spradling" <kspradling@kc.rr.com>
>> To: <vectorlist@vectorlist.org>
>> Sent: Sunday, March 22, 2009 4:16 PM
>> Subject: VECTOR: A/R II voltage running up
>>
>>
>>> Hi,
>>>
>>> Rebuilding my Tempest P/S after noticing the voltage was at 6.05 volts.
>>> Attempted to adjust it and could only get down to 5.4vdc. Installed the
>>> Bob Roberts shotgun repair kit, big blue replacement, new pcb and
>>> harness connector kit and am still having the same issues. Measuring a
>>> voltage drop of about 0.125 on the +5vdc from P/S to Game PCB and less
>>> than .02 on the gnd. No burn marks on the pcb and edge connectors are
>>> in good shape.
>>>
>>> Who knows anything about looking for issues in the feedback system?
>>> Should I just start lifting resistors in the feedback area and taking
>>> readings to see if any have gone open? The pot does adjust the voltage,
>>> it just won't go down any further. Have tested all diodes on that side
>>> as well.
>>>
>>> Thanks,
>>>
>>> Kirk S.
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>>>
>>
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>
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Received on Mon Mar 23 01:54:30 2009