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Just go slowly and be careful. You will also want to take some ESD precautions. Take pictures of everything before you take is apart.

73

-Jim
NU0C

On Thu, 25 Jan 2024 16:37:26 -0800
"Rick K8EZB" <frboswell@...> wrote:

Jim,

Thanks for the cap info. Will get an orrder in shortly. Want to do some in-circuit testing first. I am beginning to think I might actually be able to do this!

Best,

RB

--

73

-Jim
NU0C

Now into troubleshooting this RV75. I have the two boards out and am working on learning how the components on each board relate to the circuit diagram in my RV75 manual. I am not finding a 1:1 correspondence between the manual diagram and the components on the RF & Analog board. In particular, one of the damaged resistors does not appear to be on the circuit diagram and several small value bypass capacitors shown in the diagram I am unable to find on the board. In tracing the circuits involved with the burned resistors it is apparent that both of these are in the 13v circuits switched by S1.? ?My manual is dated December 1982 and the board in question has the designation " 6020D? 1982" etched into the copper at the edge of the board. I am wondering why my board and manual disagree; apparently the board or manual were changed over time. .Any guidance on this?

I have done a quick and dirty in-circuit check of the electrolytics on both boards and am seeing values within about 10 per cent with the exception of two caps on the digital board which show around 1000 mfd when the caps are spec'd at 22 mfd; I havent yet traced this circuit to see if there is a reason elsewhere why this reading is not closer to the listed cap values but I suspect the tester is seeing another connected capacitor elsewhere in the circuit. I'll get to this soon.

Thanks for any guidance.

Best,
Rick
K8EZB

The RV75 does seem to be poorly documented. I wouldn't worry so much that it doesn't exactly match the schematic, but rather that the parts that ARE there are working.

Don't spend a lot of time testing the caps. They are all old. Just replace them.

73

-Jim
NU0C

On Mon, 29 Jan 2024 10:08:48 -0800
"Rick K8EZB" <frboswell@...> wrote:

Now into troubleshooting this RV75. I have the two boards out and am working on learning how the components on each board relate to the circuit diagram in my RV75 manual. I am not finding a 1:1 correspondence between the manual diagram and the components on the RF & Analog board. In particular, one of the damaged resistors does not appear to be on the circuit diagram and several small value bypass capacitors shown in the diagram I am unable to find on the board. In tracing the circuits involved with the burned resistors it is apparent that both of these are in the 13v circuits switched by S1.? ?My manual is dated December 1982 and the board in question has the designation " 6020D? 1982" etched into the copper at the edge of the board. I am wondering why my board and manual disagree; apparently the board or manual were changed over time. .Any guidance on this?

I have done a quick and dirty in-circuit check of the electrolytics on both boards and am seeing values within about 10 per cent with the exception of two caps on the digital board which show around 1000 mfd when the caps are spec'd at 22 mfd; I havent yet traced this circuit to see if there is a reason elsewhere why this reading is not closer to the listed cap values but I suspect the tester is seeing another connected capacitor elsewhere in the circuit. I'll get to this soon.

Thanks for any guidance.

Best,
Rick
K8EZB

--

73

-Jim
NU0C

....except for the Tantalum capacitors. If they are not shorted or burned leave them alone.

73

-Jim
NU0C

On Mon, 29 Jan 2024 14:32:45 -0600
"Jim Shorney via groups.io" <jimNU0C@...> wrote:

Don't spend a lot of time testing the caps. They are all old. Just replace them.

--

73

-Jim
NU0C

Just replace them.

I'll get to this but first trying to do a top level assessment of what the problem might be. Since the caps seem OK for now, I'll look for other possible causes first. My approach is to attempt to get this gear limping along and then tidy up the seconday issues. So far I have only about an hour of time into this, and am seeing all this for the first time; still much to learn. Per your suggestions, going slow and taking plenty of pictures!

Thanks for your response.

RB

On Mon, Jan 29, 2024 at 03:59 PM, John K5MO wrote:

"Fixing" too much stuff at once can inject additional problems into the mix ,often masking the initial problem !

Been there, done that too! I wont plug in the soldering iron until I have a strong conviction as to what the problem is.?

RB

There is a method to my madness. Sub standard or failing capacitors can cause all sorts of strange problems. The RV75 was released in 1982. That's over 40 years ago.

73

-Jim
NU0C

On Mon, 29 Jan 2024 15:34:43 -0800
"Rick K8EZB" <frboswell@...> wrote:

Just replace them.

I'll get to this but first trying to do a top level assessment of what the problem might be. Since the caps seem OK for now, I'll look for other possible causes first. My approach is to attempt to get this gear limping along and then tidy up the seconday issues. So far I have only about an hour of time into this, and am seeing all this for the first time; still much to learn. Per your suggestions, going slow and taking plenty of pictures!

Thanks for your response.

RB

--

73

-Jim
NU0C

I have 2 RV75 VFOs and on both of them I started hearing strange noises when tuning across a signal. This was very noticeable on AM. The internal PTO did not make the noises. I put a scope on the voltage rails and there was all kinds of noise on them. I started removing the electrolytics 1 at a time and even though the capacitance was in spec the ESR was way off. So I replaced all of the electrolytics and the noise on the DC voltage rail was gone and the noise when tuning across signal was gone. They both have been regular use for the last 5 years with no more problems.

73, Joe Pyles KC9LAD

On Mon, Jan 29, 2024 at 11:31 PM, Joe Pyles wrote:

even though the capacitance was in spec the ESR was way off

In quickly checking ESR today I noticed this in at least one instance. All new caps ordered per Jim's parts list.

Jim: Thanks for making this so easy: go to Mouser website, enter PN's & quantity, checkout.

In looking more carefully at the 10K resistor described by Peter (aka Steve) as "broken," that description appears to be accurate on close inspection. I see no evidence of burning on the resistror body or PC board. How this would come to be broken and positioned as I found it is not at all clear, except by human intervention. This resiistor does not appear on my manual ckt diagram. OTOH, the 150 ohm resistor shows very clear evidence of burning on both the resistor body and PC board. This resistor connects to the "Enable" line via the RV75 to TR7 cable and appears to bias the PIN diode on to enable RF output. A quick check of the PIN diode seems to indicate it is OK. I'll need to look at the TR7 ckts to better understand how this is supposed to work.

I have spent considerable time visually inspecting both boards and see no obvious physical problems beyond the failed resistors. There is some evidence of rework around two DIP IC's on the digital board, but this may have been done by Drake on the production line. My current plan is to replace the defective resistors and any caps where the value or ESR is out of line. I'll also investigate the "Enable " line back into the TR7. Once this is done I dont see that I can go much farther without reassembling the RV75 and powering it up with the TR7.

RB