HP 5335A Timer / Counter - Anything i should know?

[Dr. Frank]

Some pictures of the hacks, of the PCB, options, versions and the general condition of the instrument would be nice, anyhow.

THX
Frank

[David Aurora]

Yeah, I'll do a proper look check of caps etc at some point soon, safe to say given the age it will need some love like that. Fan wiring looks shocking, so I'll assume that was someones crack at the mod. Rear relay section looks clean from the top, though I did pull it and clean pins as a quick check for other issues.

Option wise it has everything except the DVM. General condition is good, but yeah- definitely has some front end issues that have been swept under the rug and shoehorned into basic operation.

I did a little troubleshooting late last night and the signal never makes it out of A12 alive on channel A. Signal is present on channel B at the output of Q4 and off to the next board, but dead on Q12. Coax had been crossed from A12 channel A to A11 channel B and vice versa, so I guess they were running it around the damaged input channel and that's why I had to hit those settings as well as why those measurements like slew didn't work.

Jumping back I found the signal was already dead at the output of U4, EXCEPT if I set the trigger control to minimum (just clicked out of preset). In that state the waveforms match between channels, but as I raise it the signal disappears. Trigger adjustment control itself works fine and ATL signal appears correct. I stopped there, I'll try to get in a bit further on my lunch break if I get a chance, but that definitely gives me some suspicions to check.

[TERRA Operative]

Another thing to check as a matter of course, especially on abused units is the 50ohm termination resistors, they can end up burnt out if care wasn't taken.

I have an entire spare working unit not to be parted out (sans display window.. why do people use harsh chemicals to clean these???) but I'm not sure if I have accumulated any spare PCB's yet.. If I come across any in my piles of gear, I'll let you know. The input chips are the special ones and can be hard to find.

[David Aurora]

Another thing to check as a matter of course, especially on abused units is the 50ohm termination resistors, they can end up burnt out if care wasn't taken.

I have an entire spare working unit not to be parted out (sans display window.. why do people use harsh chemicals to clean these???) but I'm not sure if I have accumulated any spare PCB's yet.. If I come across any in my piles of gear, I'll let you know. The input chips are the special ones and can be hard to find.

Thanks!

I'm thinking if I hit a wall on ICs I may steal from the B channel to get a fully functional A channel as a temporary solution so I can at least test the main functions properly.

[David Aurora]

Confirmed, U5 is cooked. Good thing I haggled when I bought this, I was told it was working properly but went in assuming it was a crapshoot.

And so the chip hunt begins!

[David Aurora]

Just swapped U2 and U5, unit now counts as it should on channel A (and obviously now not on channel B). So that's some progress I guess, I don't have to press a bunch of buttons at power up to make it work.

Still no action on rise/fall and slew modes though. I can't be stuffed digging in any more today to figure out why. Given that those modes enable COM A mode though, I'm guessing there's some kind of internal routing that uses both channels for these modes and with one dead channel it doesn't work?

[Dr. Frank]

Just swapped U2 and U5, unit now counts as it should on channel A (and obviously now not on channel B). So that's some progress I guess, I don't have to press a bunch of buttons at power up to make it work.

Still no action on rise/fall and slew modes though. I can't be stuffed digging in any more today to figure out why. Given that those modes enable COM A mode though, I'm guessing there's some kind of internal routing that uses both channels for these modes and with one dead channel it doesn't work?

Correct, those modes require both working channels, because you need two distinct trigger levels between you measure the Time Interval.

[David Aurora]

Just swapped U2 and U5, unit now counts as it should on channel A (and obviously now not on channel B). So that's some progress I guess, I don't have to press a bunch of buttons at power up to make it work.

Still no action on rise/fall and slew modes though. I can't be stuffed digging in any more today to figure out why. Given that those modes enable COM A mode though, I'm guessing there's some kind of internal routing that uses both channels for these modes and with one dead channel it doesn't work?

Correct, those modes require both working channels, because you need two distinct trigger levels between you measure the Time Interval.

Thanks for confirming! Back to the naughty shelf it goes until I find another IC

[Dr. Frank]

Just swapped U2 and U5, unit now counts as it should on channel A (and obviously now not on channel B). So that's some progress I guess, I don't have to press a bunch of buttons at power up to make it work.

Still no action on rise/fall and slew modes though. I can't be stuffed digging in any more today to figure out why. Given that those modes enable COM A mode though, I'm guessing there's some kind of internal routing that uses both channels for these modes and with one dead channel it doesn't work?

Correct, those modes require both working channels, because you need two distinct trigger levels between you measure the Time Interval.

Thanks for confirming! Back to the naughty shelf it goes until I find another IC

Better search for a front end replacement, as this IC might be unobtainium.
This double channel electronics was identical to another HP 500MHz counter, I just don't remember the model No. This other, elder counter was quite cheap to acquire.

[David Aurora]

Just swapped U2 and U5, unit now counts as it should on channel A (and obviously now not on channel B). So that's some progress I guess, I don't have to press a bunch of buttons at power up to make it work.

Still no action on rise/fall and slew modes though. I can't be stuffed digging in any more today to figure out why. Given that those modes enable COM A mode though, I'm guessing there's some kind of internal routing that uses both channels for these modes and with one dead channel it doesn't work?

Correct, those modes require both working channels, because you need two distinct trigger levels between you measure the Time Interval.

Thanks for confirming! Back to the naughty shelf it goes until I find another IC

Better search for a front end replacement, as this IC might be unobtainium.
This double channel electronics was identical to another HP 500MHz counter, I just don't remember the model No. This other, elder counter was quite cheap to acquire.

Yeah, I'll keep an eye out for whatever I can get to button this thing back up I guess. IC's, whole boards, junked units, other units with the same part, whatever pops up first and gets it working again 

Frustratingly I didn't even really want it but grabbed it because I'm always loaning gear to people and thought another counter couldn't hurt. But I think by the time I sort this out I'll have pumped far more effort into it than it was worth 

[TERRA Operative]

I had a look through my spare PCB's. Unfortunately while I have the two 'motherboards' I don't have the input board.

I'll keep an eye out locally if one pops up though.

[David Aurora]

I had a look through my spare PCB's. Unfortunately while I have the two 'motherboards' I don't have the input board.

I'll keep an eye out locally if one pops up though.

Thanks!

I asked on an HP group as well, and I'm watching eBay. With any luck something will turn up somewhere

[Wrenches of Death]

Also, there is an electrolytic cap on the PSU section, just next to the small green edge connector that I have found is really needing replacement in 2 out of 2 units I've poked at so far.

All of mine are buttoned up and stacked right now.

Is this the small upright radial leaded Sprague capacitor designated as A1C2?

The manual lists it as 100uf @ 15VDC. If so, I'll drop a few in my Mouser cart and snag them on the next order.

Were yours leaking, bulging, or failing electrically?

Many thanks in advance!

WoD

[TERRA Operative]

Yeah, that's the one. Mine tested almost no capacitance so I think they dried out or something.

I just replaced them with a 105degree rated cap. I think one of my two units even got the exact original type capacitor )possibly higher voltage though) as they are still available new, but it's not a critical application here I think so any decent capacitor would be fine.

[Wrenches of Death]

Yeah, that's the one. Mine tested almost no capacitance so I think they dried out or something.

Thanks. I just added them to my cart and pulled the trigger. All three counters seem to be behaving other than one of the little transistor sized relays for option 40. The easiest way to check it was to simply remove the driver transisor. The relay is bad and tough as hell to find new for a reasonable price. I've got a parts hulk around here that I'll eventually get around to robbing a used relay from.

If I don't forget, I plan to test the three original A1C2 caps after I replace them and will post the results. With both of yours being bad, this may be a common failure component and well worth replacing in any 5335A.

Thanks again!
WoD

[Wrenches of Death]

Yeah, that's the one. Mine tested almost no capacitance so I think they dried out or something.

I received the Mouser order this morning and just finished replacing the A1C2 caps in three 5335A's, and removing and testing one from my parts hulk.

I installed 105C 180uf @ 25V caps.

I tested the old ones that I removed and found the following:

All were Sprague 672D 100uf @ 15V rated at 105C

A1C2 from SN 2152A024xx tested @ ~ 50pf with a date code of 8121H
A1C2 from SN 2424A061xx tested @ ~620pf with a date code of 8337H
A1C2 from SN 2448A066xx tested @ ~110pf with a date code of 8426H1
A1C2 from SN 2820A120xx tested @ ~143pf with a date code of 8812H

With the two that you tested and found bad, I think I'd go out on a limb here and state  that it would be a safe bet to automatically replace A1C2 in any 5335A that crossed your path.

Thanks for your post that brought these to my attention!

I just pulled A1C2 from my parts hulk and added it to the above list. It's even worse than the other three.

WoD

[TERRA Operative]

Yep, I agree. Mine tested about the same capacitance too.

[Wrenches of Death]

Yep, I agree. Mine tested about the same capacitance too.

I had to place another parts order and went ahead and added a couple of pair of replacements for the 2000uf A1C12 and A1C13. I pulled the originals on the 2424A prefix counter this morning and they both measured 2100+uf with good D and ESR. I put them both back in for now.

While I had it apart, I pulled the 17,000uf A1C14 and tested it. It was in the high 15,000uf range. D and ESR were acceptable. I then pulled the smaller 8000uf A1C16 and it tested in the mid 7000uf range.

Both of these were within the -10% tolerance for those two cap positions, but I can foresee possibly having to replace them somewhere down the line. To be honest, I trust 40 year old US made high end Sprague caps more than the vast majority of the stuff that's out there on the market today.

Did you test any of these four caps in your counters?

WoD

[TERRA Operative]

I took a chance and didn't bother with the big ones. From my experience, the big caps generally tend to last without much trouble.

I probably should throw them on the 4276A LCZ meter to check them.... I'll add it to the 'to-do' list.... A rather long list that is.