Data Precision 8200 with 1kV option - Page 1
Forum section: electronics / testgear

author: Lifeborne
author_rank: Contributor
timestamp: July 30, 2020, 02:07:23 pm
content: Trying to revive my 8200 DP with 1KV option and need info for a burned part that is underneath the shielded HV box. Pictures to follow.

author: Lifeborne
author_rank: Contributor
timestamp: July 30, 2020, 02:33:08 pm
content: Here a pic with the shielded HV metal box removed and the precision voltage divider de-soldered. The part value I need is the burned resistor R9 right above C2. Any help will be great.[ Specified attachment is not available ]

author: Lifeborne
author_rank: Contributor
timestamp: July 30, 2020, 02:41:31 pm
content: This is the entire HV module installed, where there usually an empty spot.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 30, 2020, 03:38:44 pm
content: Hi,I have the Data Precision (Analogic) 8200 manual. Unfortunately the HV module is not in the manual.Since I am a nice guy, I took mine apart.The answer is R9 is 4.7Yellow Purple Gold GoldThis was confirmed by measurement.Take care!!Best regards,Jay_Diddy_B

author: Lifeborne
author_rank: Contributor
timestamp: July 30, 2020, 08:02:05 pm
content: Thanks for the help. I have a self-hand drawn schematic of the HV module, but I am not totally sure of its completion. So far the theoretical operation is there.

author: srb1954
author_rank: Super Contributor
timestamp: July 31, 2020, 08:59:38 am
content: Please post your schematic. I, along with many other 8200 owners, would be very interested.

author: Lifeborne
author_rank: Contributor
timestamp: July 31, 2020, 02:24:35 pm
content: The theoretical operation of the DP 8200 is comparable to the EDC 521 HV section. My HV does not operate currently, not sure what the fault is but it still indicates the "ERROR" even though the module is installed. I have reviewed the schematic, but can't pin-point how the processor knows the HV is attached. Can anyone clarify.[ Specified attachment is not available ]Disclaimer:The attachment diagrams are for educational purpose and should not be replicated partially or entirely unless permission is granted from the original designer (Data Precision Corp). It should also be understood that the completeness of circuit has not been verified and the operation of the circuit has not been verified.

author: Lifeborne
author_rank: Contributor
timestamp: July 31, 2020, 02:35:21 pm
content: Still new at posting pics/ info., this is the main module.Data Precision 8200-Model.pdf(223.18 kB - downloaded 255 times.)Disclaimer:The attachment diagrams are for educational purpose and should not be replicated partially or entirely unless permission is granted from the original designer (Data Precision Corp). It should also be understood that the completeness of circuit has not been verified and the operation of the circuit has not been verified.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 31, 2020, 03:07:17 pm
content: Hi,When I took mine apart yesterday I had a look at the HV daughter module.I believe Z1 is used as an oscillator.Z2 divides the oscillation frequency by 2. This make sure that there is symmetrical drive on the two MOSFETs Q5 and Q6.These MOSFETs push-pull the primary of the transformer Y1.The center tap of the transformer is fed via E9 and R9 (on the motherboard) by Q4.Q4 emitter voltage controls the HV output.The HV secondary is rectified by CR3 and CR4.The feedback and control circuits are on the mother board.I am not sure how the HV option is detected.Regards,Jay_Diddy_B

author: Lifeborne
author_rank: Contributor
timestamp: July 31, 2020, 04:23:38 pm
content: Jay_D described the operation perfectly.This is the output I get from the oscillator to the MOSFETs Q5 and Q6 Gate (0Vmax and -15Vmin, 52.25k sqaure). Is the Z1 positive supply VDD suppose to be 0V? The A2 voltage divider values I tested (out of circuit) were, 10K,10K,23.24K,10K,14.3K.The VN88AFD MOSs are Enhanced Mode, the Source of both MOSs are -15V (from the regulator on the Mother Board) and the Drain is fed via E9 and R9.I have tested all the parts but, the R9 keeps burning. The TX tested 1:10 on the secondary, it is not shorted and gives me a clean sinewave form at a frequency that must be >32 kHZ;

author: ddrl46
author_rank: Regular Contributor
timestamp: July 31, 2020, 04:28:59 pm
content: As far as I know the high voltage option is detected by putting a jumper between TP2 (the two header pins next to the big chip) on the processor card. When these two pins are connected togheter the error when switching to the 1000V range goes away.

author: Lifeborne
author_rank: Contributor
timestamp: July 31, 2020, 04:38:14 pm
content: That would make sense that the signal was external; all the HV relays operate and there is no feedback signal to the processor.

author: Lifeborne
author_rank: Contributor
timestamp: July 31, 2020, 05:35:43 pm
content: The jumper did fix the HV "Error" Thanks for the tip.

author: Lifeborne
author_rank: Contributor
timestamp: July 31, 2020, 05:39:49 pm
content: Now the only problem I have now is the HV output will only go to the value of the 130V unreg from the supply.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 31, 2020, 08:00:03 pm
content: Hi,Is it working now?Did you find out why R9 was burning up?Jay_Diddy_B

author: Lifeborne
author_rank: Contributor
timestamp: July 31, 2020, 09:19:52 pm
content: Hello,I just finished working on it and surprisingly, with the HV TX de-soldered, it worked perfectly with a 52.2Khz sinewave and 1Vpp on one half of the primary (one tap to center) which produced an output of 10Vpp. After testing the other tap of the primary, things got funky. 1Vpp produced 12Vpp. When I went back to the first tap, it was 250mVpp !!This pic below shows 1Vpp supply on upper and lower primary taps and 20Vpp out.*Still working on how to upload multiple pics in one post.

author: Lifeborne
author_rank: Contributor
timestamp: July 31, 2020, 09:26:47 pm
content: I decided to remove the HV TX from its metal shield, which I believe to be shorting the TX and created a mock-up circuit and it works now.

author: Lifeborne
author_rank: Contributor
timestamp: July 31, 2020, 09:29:25 pm
content: I dialed it up to 1KV, with caution, and it held and dialed it down 100V increments with no abnormal smells or sparks.[ Specified attachment is not available ]

author: Lifeborne
author_rank: Contributor
timestamp: July 31, 2020, 09:44:29 pm
content: The symptoms were the Q4 was getting hot and sometimes the R9 resistor would burn. When you mentioned the Q4 controlled the HV at the TX center tap ( which I thought was a center ground tap because of an old drawing I made ), I realized the only thing that could cause a surge in current to burn the resistor would be the center tap supply to the HV TX. After removing the TX can the secondary coil read 14 ohms instead of the previous 3~4 ohm. The problem was an intermittent short on the TX metal case or there is conductivity in the black mica/plastic the TX leads are soldered to.