HP1715A repair - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

WaveyDipole · 22nd May 2017, 6:56 pm

Ok, I think I have located the two resistors and have taken some measurements. I can't tell which one is which, so I will just call them Rx and Ry:

Rx A:4.63v B:5.93v Both:6.08v
Ry A:6.96v B:5.58v Both:7.14v

The pull up voltage was 6.48, so near enough to 6.5v. These readings do not seem very consistent but while testing I discovered that it is possible to get a near central trace when selecting the B channel. Also, the line on the A channel will momentarily centralise when pressing the A button but will not stay there. When B was selected, the line was just at the edge of the screen and could be adjusted. The adjustment though is fairly limited - 6 graticules on POS A and 2 graticules on POS B. Although channel B is selected, both pots seem to move the line. There is no signal. Selecting Chop or Alt also seems to move the line about a little.

BTW, contrary to my previous - evidently erroneous - reply, the plate voltages do change according to which channel combination is selected and so do the substrate assembly IC output voltages.

TonyDuell · 22nd May 2017, 7:03 pm

I thought that HP part numbers followed the following pattern :

4digit - 4digit : Component, the first group of 4 digits being the general type of component. Custom ICs, and HP-manufactured componets (like LED displays) have
this type of number.

5digit - 5digit : Subassembly (such as a PCB), the first group of digits being the model number of the instrument where first used (with leading zeros if needed). For example the CPU control (microcode) board of an HP9830 computer is a 09810-66513 as it was first used in the HP9810 calculator.

A couple of other 4-digit 'first group' codes that are worth knowing :

1826- : Linear IC
1818- : Memory device (may be ROM or RAM).
1858- : Transistor array

Note that sometimes the 'wrong' code was used, I've seen RAM with 1820- numbers.

Chris55000 · 22nd May 2017, 7:14 pm

Hi!

Did Key***** send that manual to China for scanning - it certainly looks like it!

I've just downloaded the only one I can get hold of to see if I can make a better drawing with my sPlan but it's scanned so atrociously bad it's unbeliveable!

If you feel confident about doing so, you could try removing the A3A1 Substrate Assembly from the A3 Main Module - it's held by a screw at each corner, then locate pins 4 and 16 - from what I can make out these are chassis-earth pins, then use a dvm to measure the ohms between each pin and earth and write up a little table.

Look especially for any d.c. resistance measurements between any pin and earth lower than 200R - my experience with testing unknown devices from industrial PCBs is that a chip that overheats badly has invariably got at least one or more pins very low resistance - tens of ohms typically!

Sphere in Canada have got a few of these things in at the moment - H.P. 5081-3028 @ $49 each plus S & H.

For the time being I'd remove the A3A1 hybrid and have a prod round the contacts on the A3 Module and make sure there's no obvious short-circuits, but it is beginning to look to me like the A1 hybrid might be defective in some way!

I don't have a hp 1715 myself or it's manual unfortunately, and I can understand your reluctance to spend a lot of money on better-quality documentation for a scope that may prove unrepairable!

However, although I can't make a silk-purse out of a sow's ear diagram-wise if you get really mega-stuck, and you're willing - I'm willing to come over to Leicester for an hour or two with one of my 'scopes and sit down with you for a second opinion - please PM me if you're interested - the offer is made F.O.C!!!

Chris Williams

PS!

The manual for the 1725A seems to have the same sort of hybrid in it - H.P. 5081-3023 and the circuit-diagrams in it aren't quite as atrociously bad - you might be able to download and print the vertical sections from the 1725A and see if that will help - another thought - it might be worth looking to see if there's any "H.P Journals" or "HP Bench Briefs" relavent to the 1715a and 1725a!

Chris55000 · 22nd May 2017, 7:48 pm

PS!

The manual for the 1725A seems to have the same sort of hybrid in it - H.P. 5081-3023 and the circuit-diagrams in it aren't quite as atrociously bad - you might be able to download and print the vertical sections from the 1725A and see if that will help - another thought - it might be worth looking to see if there's any "H.P Journals" or "HP Bench Briefs" relavent to the 1715a and 1725a!

PPS!

Some of the theory and adjustment diagrams in the HP 1725a manual have been used again from the 1715 - for example the "Timebase Block Diagram" which is totally unreadable in the 1715a manual has the same drawing no in the 1725a, so you might be able to put the two manuals together perhaps to make one from common parts!

WaveyDipole · 22nd May 2017, 8:13 pm

Thanks for the comments and kind offer.

Yes that is the reason for my reluctance regarding the manual. If I had more confidence that it might be repairable and worth keeping, then I would perhaps consider it.

I am no longer sure that the channel attenuators and input boards are working correctly. I did pick up a signal from the screened off section and traced it to pin 3 of the corresponding op amp in the vertical pre-amp, which I assumed to be the input point to board A3, however I have just realised that there should be a signal to points 1 and 2 (CH A and CH B input) directly on the A1 IC. There is absolutely nothing on either channel. Tracking back, there is nothing at the gate of the FET in either channel, not even on the .005 setting. It looks like I'm going to have to disassemble and have a look at the attenuator assembly. It seems odd though to have the same problem on both channels?

PJL · 22nd May 2017, 8:48 pm

Clearly bits of it are working. Maybe there are multiple faults or maybe its just been twiddled with.

1. Switch to channel B, set to centre and measure the A1 chip outputs to make sure they are roughly the same.

2. On page 5-14 are instructions for setting the channel amplifier offsets, Vertical preamplifier balance adjustments. Try this for Channel B.

PS: Just read your latest and I agree it is very unlikely. Double check all the switch settings before you start dismantling everything.

Radio Wrangler · 22nd May 2017, 9:19 pm

Oh, I dunno. Occasionally some superstar sticks too much voltage or a live transmitter into an instrument, can't figure out why he doesn't see anything, so tries the other channels....

David

HP used 5-5 digit part numbers for assemblies and their drawings and artwork associated with a specific instrument, and used 4-4 digit numbers for parts bought in or HP-made parts which were treated like bought in ones.... sometimes this meant parts shared across the corporation as commodities or sold outside like LED displays and RPGs.

WaveyDipole · 22nd May 2017, 11:06 pm

PS, Chris thanks for the 1725 manual suggestion. yes, it is much clearer and easier to work from. Thanks for the suggestions PJL. Its getting late and I'm getting tired so I will carry on maybe tomorrow or another day.

Chris55000 · 23rd May 2017, 11:05 am

Hi!

Watch this space for some (hopefully!) better paperwork. . .!

Chris Williams

WaveyDipole · 23rd May 2017, 12:17 pm

Yesterday, PJL mentioned checking the channel switching. I reported that I could see what looked like state changes on one IC. This morning I decided to have a closer look at that switching board. What I was observing was the change of state on pins 2 & 3 of U1. However, if I understand it correctly, then according to the diagram, I would expect pins 4 & 5 to change between 3.2v and 4.1v as the switches are operated, but I am not seeing that. I am seeing a constant 0v on pin 4 and a constant 4.17v pin 5. What is also inconsistent is that the voltage at pin 1 is only 3.34v and there is no pin 16 - its a 14 pin package.

Chris pointed put Sphere in Canada, and while looking at the site I noticed a searchable HP parts reference PDF which I downloaded. From this I have determined that 1820-0102 is a MC1013P. However I cannot find a datasheet for that device. Does anyone have any information on this IC please?

Chris55000 · 23rd May 2017, 12:39 pm

Hi!

I hate to see anyone struggle with very bad or no diagrams, so I've purchased one from Artek - here's the Vertical Amplifier to begin with. . .!!!

The remainder I'll post as time permits!!!

Chris Williams

karesz* · 23rd May 2017, 2:59 pm

Hello WD,
MC1013p is an old, discontinued, "10K ECL" FF _ I think in DIP-14, but I can`t find a usable datasheet, these is the best resultat. Its indentic with Fairchilds F1013XX too.
Karl

Chris55000 · 23rd May 2017, 3:05 pm

Hi!

Manual part 2. . .!!!

Chris Williams

WaveyDipole · 23rd May 2017, 4:10 pm

Chis, WOW! What a difference that makes! Thank you very very much for this. I am happy to contribute towards the cost.

Of course, it also helps if the manual is correct!

It seems that the pin assignments on U1 and U2 on figure 8-8 are incorrect. They seem to be referring to 16 pin packages, whereas this board has 14 pin packages and the pin assignments are different. I have just spent the last hour or so mapping out the board. While I had it partially removed, I checked the transistors in U3 as well and all seem OK. I still have a bit more work to do on it but once I have fully mapped it out I will post the results for future reference.

karesz, thank you for that reference. It should be helpful for diagnostic purposes and will assist in understanding the logic of the gates.

Chris55000 · 23rd May 2017, 4:25 pm

Hi!

Cover and First three sections. . .!

Chris Williams

Chris55000 · 23rd May 2017, 4:34 pm

Hi!

Theory. . .!

Chris Williams

PJL · 23rd May 2017, 4:38 pm

That's very generous Chris and what a difference!

We seem to be hoping around a bit as the previous post indicated the vertical amps were both faulty.

If you have a scope and a siggen, I would start on the vertical preamp board A1 chip to check the inputs from other vertical components.

1. Connect you siggen to channel A and and you should see the signal on your scope on the CHA INPUT on the A1 chip. Do the same for Channel B. Check the inputs are not grounded.
2. You can also check the CHA POSN and CHB POSN inputs change when the position pots are change.
3. Put the scope on the CHA SELECT input and turn off/on channel A. The circuit suggests that on should be 6.5V and off 4.5V.

WaveyDipole · 23rd May 2017, 6:31 pm

PLJ, thanks for your patience and yes I have probably got ahead of myself a bit. To anwser your questions:

Quote:

1. Connect you siggen to channel A and and you should see the signal on your scope on the CHA INPUT on the A1 chip. Do the same for Channel B. Check the inputs are not grounded.

Siggen set to 1kHz with amplitude of 4v. Started with attenuator at 1v, channel set to DC. No signal on input to CH A. Repeated with channel B and same result. Signal at input is a flat line, but offset by about 0.8v. Rotated attenuator through all settings. Pretty much the same result. The flat line moved by maybe 0.1-0.2v depending on setting but that is all.

Quote:

2. You can also check the CHA POSN and CHB POSN inputs change when the position pots are change.

Yes, the voltage at the pot wiper does change. There is also a corresponding change on the other side of R31 and R34. The voltage at the Y plates also changes - by about 10v for CH A, and by about 2v for CH B.

Quote:

3. Put the scope on the CHA SELECT input and turn off/on channel A. The circuit suggests that on should be 6.5V and off 4.5V.

On = 6.9v, Off = 5.5v.

PJL · 23rd May 2017, 7:25 pm

I guess you are already looking into the signal loss! I have to ask, but the input was definitely not set to the ground position!

The attenuator section is split into two parts, a FET used for the HF component, and U1 op-amp used for the DC and LF component. The U1 op-amp is located on the pre-amplifier board (I think) so maybe more accessible. You should be able to see your siggen signal on the +ve input and hopefully something on the output.

WaveyDipole · 23rd May 2017, 9:23 pm

Yes, set to DC not to GND.

I have been looking at this part of the circuit and I can see the signal on pin 3 (non-inverted input), but nothing at all on the output. Some voltages - particularly pins 6 & 8 - around the IC are wrong:

P1 +4.23
P2 +0.38
P3 input signal
P4 -4.65v
P5 0v
P6 -4.09
P7 +4.70
P8 -4.01

Voltages around the output transistor likewise:

E -3.41v
B -4.09v
C +9.77v

Voltage at R84 is -14.7v close to the -15 expected.

The opposite side is comparable.

It would seem that the op amp ICs are dead. The part number is 1826-0553. Thanks to the cross reference from Sphere, I have determined that it cross-references to a OP-08. This is obsolete, but I was able to find a datasheet. In the description it states that this is an improved version of an LM108A. Any suggestions as to what I could replace these with?

22nd May 2017, 6:56 pm	#21
WaveyDipole Nonode Join Date: Mar 2013 Location: Leicester, UK Posts: 2,532	Re: HP1715A repair Ok, I think I have located the two resistors and have taken some measurements. I can't tell which one is which, so I will just call them Rx and Ry: Rx A:4.63v B:5.93v Both:6.08v Ry A:6.96v B:5.58v Both:7.14v The pull up voltage was 6.48, so near enough to 6.5v. These readings do not seem very consistent but while testing I discovered that it is possible to get a near central trace when selecting the B channel. Also, the line on the A channel will momentarily centralise when pressing the A button but will not stay there. When B was selected, the line was just at the edge of the screen and could be adjusted. The adjustment though is fairly limited - 6 graticules on POS A and 2 graticules on POS B. Although channel B is selected, both pots seem to move the line. There is no signal. Selecting Chop or Alt also seems to move the line about a little. BTW, contrary to my previous - evidently erroneous - reply, the plate voltages do change according to which channel combination is selected and so do the substrate assembly IC output voltages. Last edited by WaveyDipole; 22nd May 2017 at 7:05 pm.

22nd May 2017, 7:03 pm	#22
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: HP1715A repair I thought that HP part numbers followed the following pattern : 4digit - 4digit : Component, the first group of 4 digits being the general type of component. Custom ICs, and HP-manufactured componets (like LED displays) have this type of number. 5digit - 5digit : Subassembly (such as a PCB), the first group of digits being the model number of the instrument where first used (with leading zeros if needed). For example the CPU control (microcode) board of an HP9830 computer is a 09810-66513 as it was first used in the HP9810 calculator. A couple of other 4-digit 'first group' codes that are worth knowing : 1826- : Linear IC 1818- : Memory device (may be ROM or RAM). 1858- : Transistor array Note that sometimes the 'wrong' code was used, I've seen RAM with 1820- numbers.

22nd May 2017, 7:14 pm	#23
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,864	Re: HP1715A repair Hi! Did Key***** send that manual to China for scanning - it certainly looks like it! I've just downloaded the only one I can get hold of to see if I can make a better drawing with my sPlan but it's scanned so atrociously bad it's unbeliveable! If you feel confident about doing so, you could try removing the A3A1 Substrate Assembly from the A3 Main Module - it's held by a screw at each corner, then locate pins 4 and 16 - from what I can make out these are chassis-earth pins, then use a dvm to measure the ohms between each pin and earth and write up a little table. Look especially for any d.c. resistance measurements between any pin and earth lower than 200R - my experience with testing unknown devices from industrial PCBs is that a chip that overheats badly has invariably got at least one or more pins very low resistance - tens of ohms typically! Sphere in Canada have got a few of these things in at the moment - H.P. 5081-3028 @ $49 each plus S & H. For the time being I'd remove the A3A1 hybrid and have a prod round the contacts on the A3 Module and make sure there's no obvious short-circuits, but it is beginning to look to me like the A1 hybrid might be defective in some way! I don't have a hp 1715 myself or it's manual unfortunately, and I can understand your reluctance to spend a lot of money on better-quality documentation for a scope that may prove unrepairable! However, although I can't make a silk-purse out of a sow's ear diagram-wise if you get really mega-stuck, and you're willing - I'm willing to come over to Leicester for an hour or two with one of my 'scopes and sit down with you for a second opinion - please PM me if you're interested - the offer is made F.O.C!!! Chris Williams PS! The manual for the 1725A seems to have the same sort of hybrid in it - H.P. 5081-3023 and the circuit-diagrams in it aren't quite as atrociously bad - you might be able to download and print the vertical sections from the 1725A and see if that will help - another thought - it might be worth looking to see if there's any "H.P Journals" or "HP Bench Briefs" relavent to the 1715a and 1725a! __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! Last edited by Chris55000; 22nd May 2017 at 7:32 pm.

22nd May 2017, 7:48 pm	#24
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,864	Re: HP1715A repair PS! The manual for the 1725A seems to have the same sort of hybrid in it - H.P. 5081-3023 and the circuit-diagrams in it aren't quite as atrociously bad - you might be able to download and print the vertical sections from the 1725A and see if that will help - another thought - it might be worth looking to see if there's any "H.P Journals" or "HP Bench Briefs" relavent to the 1715a and 1725a! PPS! Some of the theory and adjustment diagrams in the HP 1725a manual have been used again from the 1715 - for example the "Timebase Block Diagram" which is totally unreadable in the 1715a manual has the same drawing no in the 1725a, so you might be able to put the two manuals together perhaps to make one from common parts! __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

22nd May 2017, 8:13 pm	#25
WaveyDipole Nonode Join Date: Mar 2013 Location: Leicester, UK Posts: 2,532	Re: HP1715A repair Thanks for the comments and kind offer. Yes that is the reason for my reluctance regarding the manual. If I had more confidence that it might be repairable and worth keeping, then I would perhaps consider it. I am no longer sure that the channel attenuators and input boards are working correctly. I did pick up a signal from the screened off section and traced it to pin 3 of the corresponding op amp in the vertical pre-amp, which I assumed to be the input point to board A3, however I have just realised that there should be a signal to points 1 and 2 (CH A and CH B input) directly on the A1 IC. There is absolutely nothing on either channel. Tracking back, there is nothing at the gate of the FET in either channel, not even on the .005 setting. It looks like I'm going to have to disassemble and have a look at the attenuator assembly. It seems odd though to have the same problem on both channels?

22nd May 2017, 8:48 pm	#26
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: HP1715A repair Clearly bits of it are working. Maybe there are multiple faults or maybe its just been twiddled with. 1. Switch to channel B, set to centre and measure the A1 chip outputs to make sure they are roughly the same. 2. On page 5-14 are instructions for setting the channel amplifier offsets, Vertical preamplifier balance adjustments. Try this for Channel B. PS: Just read your latest and I agree it is very unlikely. Double check all the switch settings before you start dismantling everything.

22nd May 2017, 9:19 pm	#27
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,858	Re: HP1715A repair Oh, I dunno. Occasionally some superstar sticks too much voltage or a live transmitter into an instrument, can't figure out why he doesn't see anything, so tries the other channels.... David HP used 5-5 digit part numbers for assemblies and their drawings and artwork associated with a specific instrument, and used 4-4 digit numbers for parts bought in or HP-made parts which were treated like bought in ones.... sometimes this meant parts shared across the corporation as commodities or sold outside like LED displays and RPGs. __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

22nd May 2017, 11:06 pm	#28
WaveyDipole Nonode Join Date: Mar 2013 Location: Leicester, UK Posts: 2,532	Re: HP1715A repair PS, Chris thanks for the 1725 manual suggestion. yes, it is much clearer and easier to work from. Thanks for the suggestions PJL. Its getting late and I'm getting tired so I will carry on maybe tomorrow or another day.

23rd May 2017, 11:05 am	#29
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,864	Re: HP1715A repair Hi! Watch this space for some (hopefully!) better paperwork. . .! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

23rd May 2017, 12:17 pm	#30
WaveyDipole Nonode Join Date: Mar 2013 Location: Leicester, UK Posts: 2,532	Re: HP1715A repair Yesterday, PJL mentioned checking the channel switching. I reported that I could see what looked like state changes on one IC. This morning I decided to have a closer look at that switching board. What I was observing was the change of state on pins 2 & 3 of U1. However, if I understand it correctly, then according to the diagram, I would expect pins 4 & 5 to change between 3.2v and 4.1v as the switches are operated, but I am not seeing that. I am seeing a constant 0v on pin 4 and a constant 4.17v pin 5. What is also inconsistent is that the voltage at pin 1 is only 3.34v and there is no pin 16 - its a 14 pin package. Chris pointed put Sphere in Canada, and while looking at the site I noticed a searchable HP parts reference PDF which I downloaded. From this I have determined that 1820-0102 is a MC1013P. However I cannot find a datasheet for that device. Does anyone have any information on this IC please? Attached Thumbnails

23rd May 2017, 2:59 pm	#32
karesz* Heptode Join Date: Jun 2010 Location: Zurich, Switzerland Posts: 538	Re: HP1715A repair Hello WD, MC1013p is an old, discontinued, "10K ECL" FF _ I think in DIP-14, but I can`t find a usable datasheet, these is the best resultat. Its indentic with Fairchilds F1013XX too. Karl Last edited by karesz; 23rd May 2017 at 3:06 pm.*

23rd May 2017, 4:10 pm	#34
WaveyDipole Nonode Join Date: Mar 2013 Location: Leicester, UK Posts: 2,532	Re: HP1715A repair Chis, WOW! What a difference that makes! Thank you very very much for this. I am happy to contribute towards the cost. Of course, it also helps if the manual is correct! It seems that the pin assignments on U1 and U2 on figure 8-8 are incorrect. They seem to be referring to 16 pin packages, whereas this board has 14 pin packages and the pin assignments are different. I have just spent the last hour or so mapping out the board. While I had it partially removed, I checked the transistors in U3 as well and all seem OK. I still have a bit more work to do on it but once I have fully mapped it out I will post the results for future reference. karesz, thank you for that reference. It should be helpful for diagnostic purposes and will assist in understanding the logic of the gates.

23rd May 2017, 4:38 pm	#37
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: HP1715A repair That's very generous Chris and what a difference! We seem to be hoping around a bit as the previous post indicated the vertical amps were both faulty. If you have a scope and a siggen, I would start on the vertical preamp board A1 chip to check the inputs from other vertical components. 1. Connect you siggen to channel A and and you should see the signal on your scope on the CHA INPUT on the A1 chip. Do the same for Channel B. Check the inputs are not grounded. 2. You can also check the CHA POSN and CHB POSN inputs change when the position pots are change. 3. Put the scope on the CHA SELECT input and turn off/on channel A. The circuit suggests that on should be 6.5V and off 4.5V.

23rd May 2017, 7:25 pm	#39
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: HP1715A repair I guess you are already looking into the signal loss! I have to ask, but the input was definitely not set to the ground position! The attenuator section is split into two parts, a FET used for the HF component, and U1 op-amp used for the DC and LF component. The U1 op-amp is located on the pre-amplifier board (I think) so maybe more accessible. You should be able to see your siggen signal on the +ve input and hopefully something on the output.

23rd May 2017, 9:23 pm	#40
WaveyDipole Nonode Join Date: Mar 2013 Location: Leicester, UK Posts: 2,532	Re: HP1715A repair Yes, set to DC not to GND. I have been looking at this part of the circuit and I can see the signal on pin 3 (non-inverted input), but nothing at all on the output. Some voltages - particularly pins 6 & 8 - around the IC are wrong: P1 +4.23 P2 +0.38 P3 input signal P4 -4.65v P5 0v P6 -4.09 P7 +4.70 P8 -4.01 Voltages around the output transistor likewise: E -3.41v B -4.09v C +9.77v Voltage at R84 is -14.7v close to the -15 expected. The opposite side is comparable. It would seem that the op amp ICs are dead. The part number is 1826-0553. Thanks to the cross reference from Sphere, I have determined that it cross-references to a OP-08. This is obsolete, but I was able to find a datasheet. In the description it states that this is an improved version of an LM108A. Any suggestions as to what I could replace these with?