HP 8640B

[beerbarrel]

Picked up a HP 8640B for a song. When I powered it up, the counter
display was inop. After removing the cover, I noticed that the LED for
the 5V regulator card was not lit. I removed the card and found that
the fuse was blown. Well, needless to say, the new fuse blew
instantly. My question is this: Has anyone ever torn into one of these
that might have had this problem? I thought that I might ask before I
dug any deeper.

Thanks,
Tracy

 

[nanu]

Picked up a HP 8640B for a song. When I powered it up, the counter
display was inop. After removing the cover, I noticed that the LED for
the 5V regulator card was not lit. I removed the card and found that
the fuse was blown. Well, needless to say, the new fuse blew
instantly. My question is this: Has anyone ever torn into one of these
that might have had this problem? I thought that I might ask before I
dug any deeper.

Thanks,
Tracy

First thing is to check the 5V bus for a short. If that is OK then
check the regulator card and external pass transistor for problems.
A little patience and I'm sure you'll find the problem. Good luck.

Nanu

 

[beerbarrel]

First thing is to check the 5V bus for a short. If that is OK then
check the regulator card and external pass transistor for problems.
A little patience and I'm sure you'll find the problem. Good luck.

Nanu

Thanks for the heads up Nanu. The bus looks good as does the card
components. Tomorrow I'll check the pass transistor which is a 3055. I
have a sneaking suspicion that is my problem.

Tracy

 

[beerbarrel]

the power transistor on the botton side comes loose! tighten the
screws, also check for bad caps. other than that if you got the
doubler option for 1 Ghz, you have something there.
its an easy thing to repair/

Found out that emitter to collector was shorted in the pass
transistor. They are very easy to replace. I noticed that it had been
replaced before at some point. They used a mica insulator between the
transistor and ground. The insulator was broken. I think the collector
might have been grounded. I had a 3055 to replace it. Now I just have
to get some of those hard to find little fuses that solder onto the
regulator card. I only have 35 dollars in the generator so if it never
works I'm not out too much.

Thanks,
Tracy

 

[beerbarrel]

i have 2 of those units with the 1 Ghz option.
old but very nice with the hard line feeds in side ect. )
P.S.,
make sure you lubricate the range selector universal because the
original grease (safe for plastics) tends to harden up. also check for
alignment and make sure there isn't any slack between the joints.

Dumb question time...how do ypu ID the card that has the 1 ghz option.
As of yet, I have not powered up the unit for more than a few seconds.

Thanks for the tips. I also found info on the problems with the delrin
gears.

Tracy

 

[beerbarrel]

Hmm, i not sure about that, i also got these 2 units from ebay, the
selector dial has the 1024 position on it, when you snap the switch over
to the mode your freq counter should display it.
as far as i know its simply a doubler module put in there.

It does have the 1024 range on the switch. Maybe that's a good sign
eh?

I won't know until I get a fuse for sure.

Tracy

 

[Jamie]

Picked up a HP 8640B for a song. When I powered it up, the counter
display was inop. After removing the cover, I noticed that the LED for
the 5V regulator card was not lit. I removed the card and found that
the fuse was blown. Well, needless to say, the new fuse blew
instantly. My question is this: Has anyone ever torn into one of these
that might have had this problem? I thought that I might ask before I
dug any deeper.

Thanks,
Tracy

the power transistor on the botton side comes loose! tighten the
screws, also check for bad caps. other than that if you got the
doubler option for 1 Ghz, you have something there.
its an easy thing to repair/

 

[Jamie]

Found out that emitter to collector was shorted in the pass
transistor. They are very easy to replace. I noticed that it had been
replaced before at some point. They used a mica insulator between the
transistor and ground. The insulator was broken. I think the collector
might have been grounded. I had a 3055 to replace it. Now I just have
to get some of those hard to find little fuses that solder onto the
regulator card. I only have 35 dollars in the generator so if it never
works I'm not out too much.

Thanks,
Tracy

i have 2 of those units with the 1 Ghz option.
old but very nice with the hard line feeds in side ect. )
P.S.,
make sure you lubricate the range selector universal because the
original grease (safe for plastics) tends to harden up. also check for
alignment and make sure there isn't any slack between the joints.

 

[beerbarrel]

Picked up a HP 8640B for a song. When I powered it up, the counter
display was inop. After removing the cover, I noticed that the LED for
the 5V regulator card was not lit. I removed the card and found that
the fuse was blown. Well, needless to say, the new fuse blew
instantly. My question is this: Has anyone ever torn into one of these
that might have had this problem? I thought that I might ask before I
dug any deeper.

Thanks,
Tracy

I replaced the pass transistor. I installed a 5 amp fuse. It calls for
a 3 amp. I did not have one so that will have to wait a few days. The
transistor runs mighty hot. Is that normal for this particular
generator? It seems to work fine though. I noticed whomever replaced
the last transistor did not use any conductive paste. I'm thinking
that may be some of the heat issue.

Tracy

 

[Jamie]

Dumb question time...how do ypu ID the card that has the 1 ghz option.
As of yet, I have not powered up the unit for more than a few seconds.

Thanks for the tips. I also found info on the problems with the delrin
gears.

Tracy

Hmm, i not sure about that, i also got these 2 units from ebay, the
selector dial has the 1024 position on it, when you snap the switch over
to the mode your freq counter should display it.
as far as i know its simply a doubler module put in there.

 

[Fred McKenzie]

It does have the 1024 range on the switch. Maybe that's a good sign
eh?

Tracy-

Apparently the doubler can be added to one that doesn't have it. As I
recall, the internal counter displays frequencies in the 1024 range, even
if the doubler is not there. I have the impression that the counter is
not connected to the output, but to an earlier stage, and displays a
calculated value.

Look at the HP label that has "OPT" and see if any are listed. I think
the doubler is option 3.

If you need a manual, do a search for TM 9-4935-601-14-7&P.pdf. It is
about 10 Megabytes.

Fred

 

[Jamie]

I replaced the pass transistor. I installed a 5 amp fuse. It calls for
a 3 amp. I did not have one so that will have to wait a few days. The
transistor runs mighty hot. Is that normal for this particular
generator? It seems to work fine though. I noticed whomever replaced
the last transistor did not use any conductive paste. I'm thinking
that may be some of the heat issue.

Tracy

mine does not run hot, you mite want to check for leaky caps.

 

[beerbarrel]

Tracy-

Apparently the doubler can be added to one that doesn't have it. As I
recall, the internal counter displays frequencies in the 1024 range, even
if the doubler is not there. I have the impression that the counter is
not connected to the output, but to an earlier stage, and displays a
calculated value.

Look at the HP label that has "OPT" and see if any are listed. I think
the doubler is option 3.

If you need a manual, do a search for TM 9-4935-601-14-7&P.pdf. It is
about 10 Megabytes.

Fred

Thanks Fred...

There were no options listed on the decal so I', inclined to believe
it is the base model.

Tracy

 

[beerbarrel]

mine does not run hot, you mite want to check for leaky caps.

I did not have any paste handy. I ordered some. I also noticed that
one of the screws that holds the transistor down will not tighten. It
seems to be stripped out. Once the paste gets here, I'll repair the
screw problem and see if that helps. If it does not, I'll move on to
other things to see where my problem might lie.

Tracy