HP 8640B S/N 2350A23618.
Modulation OFF (both AM and FM);
Output set to -30dBm.
INT/EXT (rear panel) set to INT;
connecting REF OUT (rear panel) to COUNTER INPUT (and setting INT/EXT to EXT) the counter reads:
0005.00 in the 0-10 range; 05.0000 in the 10-550 range
005.000 (x10) in the 0-10 range; 5.00000 in the 10-550 range;
05.0000 - overflow (X100) in the 0-10 range; .000000+overflow in the 10-550 range;.

The RF output frequency is correct and has the correct RF output level.
Level indicator works normally.
External counter input works OK in the 0-10Mhz range, but doubles
the reading in the 10-512Mhz range (BUT not if signal is coming from output REF (rear panel) !! as seen before..).

The "wiper" contacts on the round clear plastic rotary switches seem to be all in place: 4 on the back and
3 on the front on the band switch and 2 on the peak&deviation switch.
Connecting an external counter to the sig-gen output and comparing its readings against
the 8640B internal counter leads to the following table:
Range????? generated signal??? INT Freq counter Reads:
256-512??? 512??? ??? ??? ? ????????? 1024
?? ????????????? 256?? ? ? ? ? ? ?? ? ??? ??? 512
128-256??? 256??? ??? ? ? ?? ? ? ?? ? 1024
?? ? ? ? ? ? ? ? 128??? ? ? ? ? ? ? ?? ?? ??? 512
64-128? ? ? 128??? ?? ? ? ? ? ? ? ?? ??? 128
?? ? ? ? ? ? ? ? ? 64??? ??? ? ? ? ? ?? ? ? ? ?? 64
32-64????????? 64??? ?? ? ? ? ? ?? ? ? ??? 128
?? ? ? ? ? ? ? ? ? 32?? ? ? ? ? ? ? ?? ? ??? ??? 64
16-32?? ? ? ?? 32??? ? ? ? ? ? ?? ? ?? ??? 128
? ? ? ? ? ? ? ? ?? 16??? ? ? ? ? ? ? ? ? ? ? ??? 64
8-16? ? ? ? ? ? 16??? ? ? ? ? ? ? ?? ? ? ? ??? 8
? ? ? ? ? ? ? ? ?? ? 8?? ? ? ? ? ? ? ?? ?? ??? ??? 4
4-8? ? ? ? ? ? ? ? 8? ?? ? ? ? ? ? ?? ? ?? ? ??? 8
?? ? ? ? ? ? ? ? ? ? 4??? ? ? ? ? ? ?? ? ? ? ? ??? 4
2-4?? ? ? ? ? ? ?? 4?? ? ? ? ?? ? ?? ? ? ??? ??? 8
? ? ? ? ? ? ? ? ?? ? 2??? ? ? ? ? ? ? ? ?? ? ? ??? 4
1-2? ? ? ? ? ? ? ? 2?? ? ? ? ? ? ? ?? ?? ??? ??? 8
? ? ? ? ? ? ? ? ? ?? 1??? ? ? ? ? ? ?? ? ? ? ? ??? 4
.5-1?? ? ? ? ? ? ? 1??? ??? ? ? ? ?? ? ? ? ?? ?? 8
? ? ? ? ? ? ? ?? ? ? 0,5??? ?? ? ? ?? ? ? ? ? ??? 4

Can some 8640 guru address me to find the fault?
I have service manuals but none for my S/N. Ordered the right one at Aterk Manuals: still waiting for it.

Thanks in advance.
Emanuele.

Bonjour I dont comprendre if it was OK and now changes or it was always that way.

Please clarify, counter indication was first OK and something changes or failed or it was always bad?

The behavior of the counters depends on the option for doubler extending the highest band to 1024 MHZ.
I am sure this is a moved or oxidized contact on the band switch.

8640B options and serial number manuals are available as free PDF perhaps from BAMA archive or on an HP legacy site.

Bon Chance

Jon

Jon,
it worked fine until a couple of days ago.

No doubler installed.

You are by far more likley to have a failed counter IC, these are a unobtainable HP version of ECL logic.

George G6HIG

I don't think it's the EECL prescaler or any other EECL in the counter
assembly, it usually makes the high frequency input dead.
However I've succesfully replaced the EECL prescaler with a modern ECL
IC, that was more than 5 years ago, but it should be found in the
groups archives.
In these cases, the first thing to do is get the correct schematic and
manual for your 8640B serial prefix. This instrument went through a
lot of different revisions and
schematics can have large differences between the revisions.
Once you get the correct schematic, the usual method is following the
troubleshooting procedures. You need some good test equipment though.
Frank IZ8DWF

On Wed, Nov 24, 2021 at 9:11 AM george edmonds via groups.io
<G6HIG@...> wrote:

You are by far more likley to have a failed counter IC, these are a unobtainable HP version of ECL logic.

George G6HIG

I've received the manual.
I am going to go through the counter tests to isolate the fault.
I suspected the unobtainable? EECL front end chip.

Just in case, does anybody have experience replacing it with Motorola MC100EL31D (or with MC10EL31DG) as
described in a 1999 article from n2gx I've found on the Internet ?

Thx.
Emanuele.

On Wed, Nov 24, 2021 at 9:55 AM Emanuele Girlando via groups.io
<emanuele_girlando@...> wrote:

I've received the manual.
I am going to go through the counter tests to isolate the fault.
I suspected the unobtainable EECL front end chip.

when that IC dies, usually the counter doesn't show any count when
switched to the high frequency input.

Just in case, does anybody have experience replacing it with Motorola MC100EL31D (or with MC10EL31DG) as
described in a 1999 article from n2gx I've found on the Internet ?

I've done a similar replacement as described in the N2GX article, but
that circuit didn't work for me, I've had much better success by using
a proper transistor based level converter instead of the simple diode
level shifter he used. I've reported my changes to its schematic on
this group
years ago (it was 2014 or 2015 afair). I don't recall much of the
details now, my 8640B's counter is working fine since then, even
better than with
the original prescaler.

Frank IZ8DWF

Francesco, we cross posted.

If not EECL, what?
The most intriguing behavior is "External counter input works OK in the 0-10Mhz range, but doubles
the reading in the 10-512Mhz range (BUT not if signal is coming from output REF (rear panel) !!"

I'll double check the band switch wipers... they seem in place and none found floating inside the instrument..

On Wed, Nov 24, 2021 at 10:03 AM Emanuele Girlando via groups.io
<emanuele_girlando@...> wrote:

Francesco, we cross posted.

If not EECL, what?
The most intriguing behavior is "External counter input works OK in the 0-10Mhz range, but doubles
the reading in the 10-512Mhz range (BUT not if signal is coming from output REF (rear panel) !!"

aux output you mean? One of the rear there're two output connectors,
one is only for the 5 MHz (or 1 MHz) fixed internal reference.
The counter input works well only between a certain range of input
signal amplitude. The aux output has a fixed amplitude.
So if the counter works fine with the external input at a fixed
amplitude, I'd really check switch contacts first.
Frank

开云体育

--
Cheers Jerry

On November 24, 2021 11:43:28 AM "Jerry Meyerhoff, JDM LABS" <jerrybikes1@...> wrote:>Following this thread with keen interest.

Perhaps some advice on this problem will be applicable to my problem :
** Counter displays exactly 1/2 the output frequency on all bands **
8640B SN 1638A05395 OPT 003
The Band knob marked "EXTERNAL DOUBLER"
Always using EXTernal 10 MHz timebase as the internal appears
failed, before I got it . Also the 1/2 frequency problem always there .

Smells like could be in the 'Band-switch" logic , without digging through
manual or troubleshooting guides.

I could be wrong, as I don't have a manual in front of me, but I seem to recall that the 8640's external frequency reference input is 5MHz, not 10MHz

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

Yes, using a 10 MHz reference instead of a required 5 MHz would result in
reading half of the input frequency. 73 - Mike

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ 07731
848-245-9115

On Wed, Nov 24, 2021 at 5:50 PM Dave McGuire <mcguire@...> wrote:

On November 24, 2021 11:43:28 AM "Jerry Meyerhoff, JDM LABS" <jerrybikes1@...> wrote:>Following this thread with keen interest.

Perhaps some advice on this problem will be applicable to my problem :
** Counter displays exactly 1/2 the output frequency on all bands **
8640B SN 1638A05395 OPT 003
The Band knob marked "EXTERNAL DOUBLER"
Always using EXTernal 10 MHz timebase as the internal appears
failed, before I got it . Also the 1/2 frequency problem always there .

Smells like could be in the 'Band-switch" logic , without digging through
manual or troubleshooting guides.

I could be wrong, as I don't have a manual in front of me, but I seem to recall that the 8640's external frequency reference input is 5MHz, not 10MHz

it's actually selectable between 5 MHz and 1 MHz via jumpers located
inside the counter assembly.
And no 10 MHz.
Frank IZ8DWF

HI Dave, Mike and Frank. Another case of FRTM? first read the manual?? page 22 of 247.? 5 mc
Not sure why I thought it was 10 mc but that was a canned oscillator I had? .. Well that was quick & easy . Thanks a mil' !!!? Appreciate your kind patience ..
Next I'll have to post a ? on output attenuator missing / intermittant on some level steps along with level meter not reading .Or maybe 1st look in FAQ's .. <wink>

Happy Thanksgiving !?
--
Cheers Jerry? WA9FIY?? 11.24.2021

On 11/24/21 4:23 PM, Jerry Meyerhoff, JDM LABS wrote:

HI Dave, Mike and Frank. Another case of FRTM? first read the manual page 22 of 247.? 5 mc
Not sure why I thought it was 10 mc but that was a canned oscillator I had? .. Well that was quick & easy . Thanks a mil' !!!? Appreciate your kind patience ..

Well, the whole world uses 10MHz for everything, so it's a reasonable assumption. However, the 8640 predates that convention, and quite a few things back then used 5MHz.

Glad the group could assist you in getting it straightened out.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

开云体育

Please, can anybody confirm my initial assumption about the number of wipers that should be there?
.. 4 on the back and 3 on the front plastic rotors on the band switch and 2 on the peak&deviation switch.

My manual pictures do not show this information...

Thx
Emanuele.