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A follow-up to my previous post “RV75 Issues:” Current status following additional trouble shooting time:

?? Burned 150 ohm resistor (R218) in PTO ENABLE line on RF & Analog board: so far no cause of resistor damage apparent. The only DC path through this resistor showing on my manual ckt diag is from the TR7 ENABLE line via the PIN diode and to the TR7 RV7 connector via P207.

?? When I connect an RV7 to the TR7, the RV7 works as expected suggesting that the PTO switching circuits are working normally in the TR7, and that my problem is likely contained to the RV75.

?? Using an in-ckt test instrument, the capacitance value and ESR value for each electrolytic on both boards is fairly close to the labeled value for capacitance and fairly close to the published “typical” ESR values ?for aluminum electrolytics taking into account capacitance and voltage. My current thinking is that none of the ESR values are outliers to the extent that there is an obvious problem with the capacitor. I will change all of these caps on Jim’s recommendation but currently doubt that these are linked to the burned resistor.

?? Damaged 10K resistor (no R2xx designation, not shown on my ckt diag): The damage appears to be of a mechanical nature, and not due to heating. ??This is in a part of the ckt that does not appear to be associated with the burned resistor. ?How such damage might have occurred is a mystery. This RV75 was in Ron Baker’s shop in 2015 and got a clean bill of health.

?? My best thinking at the moment is that the evidence points (weakly) to the PIN diode as far as the burned resistor is concerned. I have new ones on the way and will change this out.?

?? There may be other problems than the burned and broken resistors and we will sort these out one step at a time.

Any informed insights most welcome as I am seeing this for the first time ever.

Thanks,

Rick

K8EZB

?

Identifying RV75 capacitors:

The components in the photo below include both resistors and capacitors on the RV75 RF & Analog board, with the capacitors having the beige colored body and are designated on the ckt diag as C224, C225 etc. I am not familiar with this type of capacitor; a link to online info appreciated. The RV75 boards have many of this type of capacitor, the failure of which can cause much difficulty.

Thanks,
Rick
K8EZB?

Based on what Mr. Google is showing me they are axial ceramic capacitors. I'm thinking now that the pink ones are also. That would explain the schematic discrepancies. I don't think I have ever heard of any failing.

73

-Jim
NU0C

On Fri, 02 Feb 2024 09:32:15 -0800
"Rick K8EZB" <frboswell@...> wrote:

Identifying RV75 capacitors:

The components in the photo below include both resistors and capacitors on the RV75 RF & Analog board, with the capacitors having the beige colored body and are designated on the ckt diag as C224, C225 etc. I am not familiar with this type of capacitor; a link to online info appreciated. The RV75 boards have many of this type of capacitor, the failure of which can cause much difficulty.

Thanks,
Rick
K8EZB

--

73

-Jim
NU0C

Not really. If it is in the position I think it is on the schematic it looks like a bypass cap. I'm guessing it is not too critical.

73

-Jim
NU0C

On Fri, 2 Feb 2024 10:37:28 -0800
"VE7PS" <ve7ps@...> wrote:

Hmmmmm...so Rick...that "broken resistor(?)" in your RV-75 that we thought
was a 10 Kohm.....didn't it have a beige body?

This complicates things a bit!

73
Peter
VE7PS

On Fri, Feb 2, 2024 at 10:08?AM Jim Shorney <jimNU0C@...> wrote:

Based on what Mr. Google is showing me they are axial ceramic capacitors.
I'm thinking now that the pink ones are also. That would explain the
schematic discrepancies. I don't think I have ever heard of any failing.

73

-Jim
NU0C

On Fri, 02 Feb 2024 09:32:15 -0800
"Rick K8EZB" <frboswell@...> wrote:

Identifying RV75 capacitors:

The components in the photo below include both resistors and capacitors

on the RV75 RF & Analog board, with the capacitors having the beige colored
body and are designated on the ckt diag as C224, C225 etc. I am not
familiar with this type of capacitor; a link to online info appreciated.
The RV75 boards have many of this type of capacitor, the failure of which
can cause much difficulty.

Thanks,
Rick
K8EZB

--

73

-Jim
NU0C

--

73

-Jim
NU0C

Jim & Peter (aka "Steve ;-) )

Thanks for your speedy and most helpful replies. Slow learner here due to no prior experience in troubleshooting/repairing electronics of the vintage of the RV75. I assumed that the components that looked like and were marked similar to resistors were resistors, but they are indeed capacitors and are accounted for in the ckt diag. And, yes, the so called "damaged 10K resistor" is actually a damaged .01 mfd bypass capacitor. Hoping to find an identical replacement but if not will substitute something suitable. Happy to hear these ceramic capacitors rarely fail. Jim in a previous post referred to tantalum capacitors and this caused some concern as I have had my share of issues with failed tantalums. I dont yet see any caps on these PC boards I recognize as tantalums.

Replacement electrolytics arrived from Mouser today so this will keep me busy for a bit.?

Best,

Rick
K8EZB

I actually don't recall if there were any Tantalums in the RV75. That was sort of a shot across the bow to the Tantalum haters. They have a bad rap due to chronic misapplication. The fact is they don't like surges. They can short or respond violently. As long as they are used within those limits they are fine. I believe that a properly cared for Tant is more reliable than a cheap electrolytic. My policy is that if they are not shorted or exploded I leave them in.

73

-Jim
NU0C

On Fri, 02 Feb 2024 12:10:04 -0800
"Rick K8EZB" <frboswell@...> wrote:

Jim & Peter (aka "Steve ;-) )

Thanks for your speedy and most helpful replies. Slow learner here due to no prior experience in troubleshooting/repairing electronics of the vintage of the RV75. I assumed that the components that looked like and were marked similar to resistors were resistors, but they are indeed capacitors and are accounted for in the ckt diag. And, yes, the so called "damaged 10K resistor" is actually a damaged .01 mfd bypass capacitor. Hoping to find an identical replacement but if not will substitute something suitable. Happy to hear these ceramic capacitors rarely fail. Jim in a previous post referred to tantalum capacitors and this caused some concern as I have had my share of issues with failed tantalums. I dont yet see any caps on these PC boards I recognize as tantalums.

Replacement electrolytics arrived from Mouser today so this will keep me busy for a bit.

Best,

Rick
K8EZB

--

73

-Jim
NU0C

I have not seen caps like this before, at least that I know of. I have seen some "computer grade" glass body axials that somewhat resembled signal diodes but were clearly caps (not in Drake gear). That might be what Steve has in his stash? I guess I just ignored the ones in my RV75 because they look like resistors and I had no reason to suspect there was any problem in that area. I was on the electrolytic hunt after some scope-age revealed ugliness on the power rails, and subsequent advice from KC9LAD. Seeing strange spurs in the Fldigi waterfall that should not have been there started the quest.

73

-Jim
NU0C

On Fri, 2 Feb 2024 12:39:21 -0800
"VE7PS" <ve7ps@...> wrote:

Rick:

Aha! OK guess that explains why I couldn't get a decent ohmeter reading on
the 10K "resistor"! Also explains why I was having trouble with the
schematic as well as you. Thanks for discovering this anomaly! I don't
recall anything like those "resistor-like" caps being used in the TR-7
anywhere - hope not - but good to know to be aware of them. I don't recall
ever coming across anything like these in the past. Maybe Drake got a deal?

Good luck with the rest of the repair. Do let us know how it ends.

73
Peter
VE7PS

On Fri, Feb 2, 2024 at 12:10?PM Rick K8EZB <frboswell@...> wrote:

Jim & Peter (aka "Steve ;-) )

Thanks for your speedy and most helpful replies. Slow learner here due to
no prior experience in troubleshooting/repairing electronics of the vintage
of the RV75. I assumed that the components that looked like and were marked
similar to resistors were resistors, but they are indeed capacitors and are
accounted for in the ckt diag. And, yes, the so called "damaged 10K
resistor" is actually a damaged .01 mfd bypass capacitor. Hoping to find an
identical replacement but if not will substitute something suitable. Happy
to hear these ceramic capacitors rarely fail. Jim in a previous post
referred to tantalum capacitors and this caused some concern as I have had
my share of issues with failed tantalums. I dont yet see any caps on these
PC boards I recognize as tantalums.

Replacement electrolytics arrived from Mouser today so this will keep me
busy for a bit.

Best,

Rick
K8EZB

--

73

-Jim
NU0C

The "classic" ceramics I have have solid green bodies. They have a code on them like "103" (0.01 uF). I don't think I ever replaced a bad one.



Steve Wedge, W1ES/4

Time flies like an arrow.? Fruit flies like a banana.

Sent with Proton Mail secure email.

I have some tubular ceramic capacitors that are probably either 25 or 50 volt parts

Steve,

The values I need are as follows:

C225, C250, C251, C252:? ?0.01 mfd

C224: 0.001 mfd

C223: 120 pf

These need to be about the same physical size as those shown in my RV75 pgoto above. Let me know what you have and what you'd like for them along with your mailing address; I'll put a check in the mail.(or PayPal if you can do this).

Thanks,

Rick
K8EZB

On Fri, Feb 2, 2024 at 03:19 PM, Steve Wedge, W1ES/4 wrote:

I’ll take a look.

Steve,

Please disregard. After substantial web surfing I have found an endless supply of Vishay ceramic axial lead caps at Mouser which I think are the modern day equivalent of those in the RV75. These dont have the same apperance but will certainly fit in the available space. Thanks for the offer.

Rick
K8EZB

Just curious, but why so many?

73

-Jim
NU0C

On Fri, 02 Feb 2024 14:36:26 -0800
"Rick K8EZB" <frboswell@...> wrote:

I have some tubular ceramic capacitors that are probably either 25 or 50
volt parts

Steve,

The values I need are as follows:

C225, C250, C251, C252:? ?0.01 mfd

C224: 0.001 mfd

C223: 120 pf

These need to be about the same physical size as those shown in my RV75 pgoto above. Let me know what you have and what you'd like for them along with your mailing address; I'll put a check in the mail.(or PayPal if you can do this).

Thanks,

Rick
K8EZB

--

73

-Jim
NU0C