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Old 26th May 2017, 6:14 pm   #61
WaveyDipole
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Default Re: HP1715A repair

Regrettably this fails at step 5.54b because it is not possible to get the trace in the centre of the screen, except by shorting the two outputs. As previously noted, the both Position control effect a change which on bot is from -0.33v to +0.33v so a central 0v can be set on each. I noticed some power supply variance although I'm not sure it is enough to explain this. in particular that the 2.2Ω resistors on the +15VF and -15VF lines are at least 3Ω, one as much as 3.6Ω, which explains variances from 14.84v through 14.69v on those lines. Likewise, +V1 is 6.11v but +V2 is 6.5v so it seems the zener on the latter is a bit off. Both should be at 6.19v and both feed into A1. The voltages at 3 and 4 from A7 (A & B sync) were correct. I am once again beginning to have doubts about A1.
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Old 26th May 2017, 7:22 pm   #62
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Default Re: HP1715A repair

It's 5.55 you should be following.
Make sure you are switched to channel A.
Attach your scope to one of the outputs (DC) so you can see any changes
Set channel A position to centre.
adjusting the 'Channel A main balance adjustment'.

If it doesn't make any difference then:
Check the CHA SELECT reads 6.5V which we think is the enabled state
Check the CHA BAL input to the P1 chip changes when you adjust the main balance control

It's not looking very promising as the obvious part next in line for failure from excessive input voltage would be the pre-amp.
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Old 26th May 2017, 8:26 pm   #63
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Default Re: HP1715A repair

Step 5.55 atempt results as follows:

Quote:
Originally Posted by PJL View Post
Make sure you are switched to channel A.
Set channel A position to centre.
Check

Quote:
Originally Posted by PJL View Post
adjusting the 'Channel A main balance adjustment'.
It made no difference...

Quote:
Originally Posted by PJL View Post
If it doesn't make any difference then:
Check the CHA SELECT reads 6.5V which we think is the enabled state
Check the CHA BAL input to the P1 chip changes when you adjust the main balance control
CH A SELECT reads 6.93v (but not low)
CH A BAL input does change as I adjust the control

Quote:
Originally Posted by PJL View Post
It's not looking very promising as the obvious part next in line for failure from excessive input voltage would be the pre-amp.

It figures since it shouldn't be possible for CH A Position control to be able to affect the CH B trace and vice versa.

Last edited by WaveyDipole; 26th May 2017 at 8:31 pm.
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Old 26th May 2017, 9:25 pm   #64
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Default Re: HP1715A repair

Hi!

I'd bought the manual whilst at work last week but I found I was still able to download another copy at home, so here's the remaining parts with my compliments!

Section 5:- Performance Check & Adjustments. . .!
Section 6:- Parts List & Exploded Views. . .!
Section 7:- Manual Changes & Errata. . .!

You should all have the lot by now!

Chris Williams
Attached Files
File Type: pdf 1715A-OSM.1.pdf (1.03 MB, 104 views)
File Type: pdf 1715A-OSM.2.pdf (1.32 MB, 687 views)
File Type: pdf 1715A-OSM.3.pdf (525.0 KB, 180 views)
__________________
It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!
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Old 26th May 2017, 9:26 pm   #65
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Default Re: HP1715A repair

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It figures since it shouldn't be possible for CH A Position control to be able to affect the CH B trace and vice versa.
With CHAN A selected, can you check with your scope on the DIFF OUT volts that Channel B control is changing it? If so, does the CH B Main balance adjustment change the DIFF OUT volts and allow you to bring the trace on screen?
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Old 26th May 2017, 10:23 pm   #66
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Default Re: HP1715A repair

Chris, thank you very much for those files. Really appreciated.

PJL, with CH A selected and using the other scope to monitor voltage changes, the channel B control seems to have no effect on either DIFF OUT, neither does the CH B main balance adjuster. Curiously, neither control has any effect when channel B is selected either.

On the other hand, the CH A position control seems to affect the DIFF OUT voltage regardless of whether CH A or CH B is selected.

BTW, I have had the substrate chip out to examine and there are not visual indications of any problems. Following Chris's suggestion I probed it a bit. Pin 16 seems to go to a line that is decoupled from earth, but I found that pins 5, 10, 20 and 22 do so checking against these I couldn't find any significant discrepancy between the A side and the B side. Any readings I obtained were either open or in the several megaohms. Once can't rule out the possibility of minor damage of course, but all I can say is that I found no obvious signs of trouble.

Last edited by WaveyDipole; 26th May 2017 at 10:29 pm.
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Old 26th May 2017, 11:50 pm   #67
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Default Re: HP1715A repair

The hope was that the FET's blew and someone has tweaked every trimmer to try to get a trace back on the screen.

The only area we haven't checked is to make sure you are not on the .005 setting as this introduces extra balance adjustments.

Other than that, a final check that the CH A/B MAIN BAL trimmers are delivering the correct voltage range to the A1 chip and have no affect on the DIFF OUT regardless of the selected channel, perhaps a check on the rail voltages to the chip, and the conclusion must be that the A1 chip is unfortunately toast.
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Old 27th May 2017, 4:30 pm   #68
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Default Re: HP1715A repair

Yes it would have been good if were as simple as that!

I did check the .005 setting, but not just the .005 setting. It behaves the same way regardless of attenuator setting.

I spent a little time today checking voltages which was easier with the chip removed as I could access all contacts. It took a while but I have confirmed that all rail voltages are correct and input/output/control voltages are balanced between both channels. CH A and CH B select and 3/4 sync were different for each channel but they are supposed to be and were correct for the channel. Things start to get unbalanced on the output only when the chip is replaced back into the circuit. I also confirmed that the correct voltage range is being delivered to the position control lines.

It looks as though we have to conclude that the A1 chip is toast.

May I take this opportunity to thank everyone for their input.


So in summary:

- needs appropriately selected replacement FETs in both channels
- Y pre-amp chip (A1) fried
- timebase running but behaving erratically
- possible problem with CRT linearity

The good points:
- CRT is working
- PSU (EHT, HT and LT) all OK
- Y amp OK
- X amp OK

A replacement A1 may be available from Sphere for $49, which may well come to well over 50 quid by the time it is posted to the UK. Its an option but I'm not sure the scope is worth spending that much on, especially as there may be other, as yet undiscovered problems waiting in the wings.

What do other members think?
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Old 28th May 2017, 10:14 am   #69
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Default Re: HP1715A repair

You could consider a number of options, not mutually exclusive:

1) Set up a search on eBay for another HP1715A as a parts donor or even one in better condition - be prepared to wait for quite some time for something to appear in the UK;

2) I could ask on your behalf on the HP_Agilent_Repair forum if anyone has a spare pre-amp IC or even a complete board. It's amazing what some of the members have stashed away;

3) As I mentioned previously, if the Siliconix J309 FET is the type you need, I can select some from my stock of E308s once someone tells me what the criterion should be. The J309 is a selected J308 with Idss from 12-30, the J310 Idss from 30-60 and the J308 an Idss from 12-60mA. The E308 is simply an earlier ceramic/epoxy package, not plastic. I should have enough E308s to select some within a couple of mA.

Just be as sure as you can be that it's the IC that is fried. I have spent many an hour chasing my tail around HP circuitry, only to find that an open circuit push button switch was messing up all the circuit conditions. Switch cleaner cured the problem completely!
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Old 28th May 2017, 2:04 pm   #70
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Default Re: HP1715A repair

Quote:
Originally Posted by Humber888 View Post
You could consider a number of options, not mutually exclusive:

1) Set up a search on eBay for another HP1715A as a parts donor or even one in better condition - be prepared to wait for quite some time for something to appear in the UK;
That's a really useful tip. Thank you.

Quote:
Originally Posted by Humber888 View Post
2) I could ask on your behalf on the HP_Agilent_Repair forum if anyone has a spare pre-amp IC or even a complete board. It's amazing what some of the members have stashed away;
That would be appreciated. I don't mind registering myself and asking though if you could give me a link to the forum. A search on HP_Agilent_Repair didn't return much and the Agilent site seems to be under maintenance at the moment.

Quote:
Originally Posted by Humber888 View Post
3) As I mentioned previously, if the Siliconix J309 FET is the type you need, I can select some from my stock of E308s once someone tells me what the criterion should be. The J309 is a selected J308 with Idss from 12-30, the J310 Idss from 30-60 and the J308 an Idss from 12-60mA. The E308 is simply an earlier ceramic/epoxy package, not plastic. I should have enough E308s to select some within a couple of mA.
Yes, thank you for that kind offer. I didn't take you up on it earlier as I decided to go with a 10 pack of cheap SMD devices for £1 initially to prove the fault. Sorting out a device with a specific Idss would be worth doing once the scope is at a point where it is up and running properly. Since neither of the originals survived, I'm not in a position to say, even with the helpful information on the subject linked in by Chris. The datasheet on these SMD FET devices states that their Idss is between 12mA and 30mA at a Vds of 10v, which seems to agree with your information.

I wonder whether the resistor test performed earlier helps? With a 1k resistor placed across D and S, the circuit seemed to be perfectly balanced with correct voltages at all of the relevant points. The nominal voltage at D is 10v and at S is 1.5v, a difference of 8.5v, so the current at which the circuit is balanced is 8.5mA. Wouldn't this then be the Idss to look for?

Of course, if anyone else out there has a 1715 and can provide the Idss value by actually measuring it against the FET, then that would certainly be appreciated.

Quote:
Originally Posted by Humber888 View Post
Just be as sure as you can be that it's the IC that is fried. I have spent many an hour chasing my tail around HP circuitry, only to find that an open circuit push button switch was messing up all the circuit conditions. Switch cleaner cured the problem completely!
That's a fair point and I would definitely want to avoid unnecessarily spending 50 quid on an IC! However, I have spent considerable time with PJL's help checking everything around the IC and am pretty confident that everything else has now been ruled out.
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Old 28th May 2017, 4:07 pm   #71
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Default Re: HP1715A repair

The HP_Agilent_Repair forum is one of the Yahoo groups. So, if you go to uk.yahoo.com and select the 'more' button along the top, you should see the groups option. Then search for something like' HP_' and it should show up. This should allow you see recent postings but you will have to join to post messages yourself and this will probably imply setting up a Yahoo account first. Try it and see.

I'm no expert on what the circuit wants from those JFETs, but the Idss cannot be 8.5mA, simply because the absolute minimum quoted is 12mA. Idss is the drain current with no volts on the gate and the current reduces as the gate goes more negative - see http://www.learningaboutelectronics....FET-transistor. So we could do with a good FET to see what the typical Idss is (or advice from one of our esteemed members).
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Old 28th May 2017, 5:15 pm   #72
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Default Re: HP1715A repair

I think I posed this link earlier:
https://nationalstocknumber.info/par...2860_012434454

Firstly, I have just checked the transistor markings again to post on Yahoo and on the ceramic one there is an additional 1 printed on the corner of the flat edge. The complete number is:

E2131 B 7851.

I couldn't find this in the HP cross-reference, but I did find a link to it online - in fact the same link as above which also refers to the F2860.

I mentioned that it lists a couple of parameters. One of them is 'maximum zero-gate-voltage drain current', which, I hadn't realised at the time is a description for the Idss, and is stated as 15mA maximum. Since we already know that the absolute minimum is 12mA, then it seems we have narrowed it down to a range of 12-15mA?

As someone pointed out, HP would have the clout to insist on having those within that narrow range selected for them . I can check my SMDs to see whether any of them come even close to that although it seems to me that the probability is likely to be rather low.

Last edited by WaveyDipole; 28th May 2017 at 5:27 pm.
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Old 29th May 2017, 11:07 am   #73
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Default Re: HP1715A repair

I would guess that the last four digits in the E2131 number make up the date code.

If the max Idss figure stated in the link is correct, then HP wanted FETs with the lowest available Idss in the J308's range of 12-60mA - namely 12-15mA. I just had a dig for my E308s and found one little bag labelled Idss ~ 15mA. I tried these on my Peak Atlas DCA75 transistor checker (changed flat battery) and found it can only read up to Idss <12mA! However, I have three that read about 11.6mA on it. The readings do vary slightly depending on which way round you connect the probes and I suspect it is reading a bit low, but probably good enough for the purpose. So I will hang on to them in case you do want to try them out.
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Old 29th May 2017, 11:53 am   #74
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Default Re: HP1715A repair

The FET is a HP part 5080-9691 and sold in matched pairs and would have been pre-selected by the manufacturer. Calculations based on the manufacturers voltages on the circuit diagram give around 9mA. The current J109 are working but running at too high a current of approximately 17mA. The 11.5mA examples should work well. Because they were selected parts for HP there is no assurance that they ever matched a listed part specification.
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Old 29th May 2017, 1:38 pm   #75
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Default Re: HP1715A repair

I have just tested the J309s that I have. All of the new ones still in packaging test at around 15-16mA. The two on the boards tested at 30mA in circuit (scope powered off and disconnected from mains). Having removed them, they tested at 20/21mA. That would still be within then 12-30mA range, but does this mean that soldering has affected them? It seem rather improbable to be just co-incidence. Testing current at 10v across the D and S of the socket with FET removed still showed about 12mA.

Humber888, I will PM you about the three that you have identified.

In the meantime I also e-mailed Sphere about the total cost of IC and am waiting to hear from them. I have also subscribed to the Yahoo group hp_agilent_equipment (I couldn't find hp_agilent_repair so assumed that hp_agilent_equipment was the one to subscribe to) and posted a request.

Last edited by WaveyDipole; 29th May 2017 at 1:49 pm.
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Old 29th May 2017, 3:48 pm   #76
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Default Re: HP1715A repair

PM received. Yes, I should have called it the HP_Agilent_Equipment forum - I managed to mash it up with this forum's 'repair' word in the title. Anyway, I saw your query so you managed to join OK. The 3 FETs are FOC - I'm never going to need all of them. What I do need to find is an old Siliconix data book with the pin layout as I can't find it easily on the net. Off to the loft.
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Old 29th May 2017, 5:14 pm   #77
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Angry Re: HP1715A repair

OK, found the Siliconix data book. Annoyingly it has a sheet on the J308, not E308. So found the sheet for the E300 for the pinout information as well. Then the scanner decided that it seemed to have lost it's software in the update to Windows 10 Creators edition. Reinstalled that and managed the scans attached. Hope you can read the attachments after uploading (pin 1 is at the bottom in case it's difficult to see). Am now going for a lie down.
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Old 29th May 2017, 5:40 pm   #78
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Default Re: HP1715A repair

Thank you for going to so much trouble to get the info from your loft!

I have just heard from Sphere and the cost of postage is a whopping $63 although that seems to be by 'expresspost air mail'. Regular parcel mail is $25 - no tracking, guarantee or insurance.

Last edited by WaveyDipole; 29th May 2017 at 5:49 pm.
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Old 29th May 2017, 6:17 pm   #79
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Default Re: HP1715A repair

Just had a timeout so didn't complete my edit! That's a total cost of about £88 for 'expresspost' or £56 for 'regular parcel mail' in pound sterling before any currency conversion or import tax costs. Does anyone know whether any import tax costs apply to parcels from Canada? Also, are Sphere a reliable source, especially when shipping via 'regular parcel mail'? I don't want to pay that kind of money only for it to be lost in the post, but £88 seems rather steep.

Last edited by WaveyDipole; 29th May 2017 at 6:40 pm.
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Old 29th May 2017, 7:58 pm   #80
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Default Re: HP1715A repair

Allow for an import charge for anything costing more than £15, it's usually a £8-12 handling fee (depending on whether it goes via Royal Mail or Parcelfarce) plus VAT at 20%.

I've only ever had a couple of items go missing from overseas and that happened during the last big postal strike. I usually just use the cheapest service as I don't need tracking and any express service will still get delayed if there are import fees, I've had numerous problems with the payment system of one of the delivery companies but that is probably a bit off topic.

David

edit,

Just checked and I have bought from Sphere once using the regular post without any problems, they did have a surcharge of 7% for using paypal, don't know if they still do though.

David

Last edited by factory; 29th May 2017 at 8:08 pm. Reason: extra info
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